Browser-Pwn

The world of Browsers is dominated by 4 major players:

• Chromium/Chrome (Blink-Engine)
• Firefox (Gecko-Engine)
• Safari (WebKit-Engine)
• Edge (Blink-Engine (former EdgeHTML-Engine)

The following is split into two parts:

• Information that helps to understand their architecture and implementation and how to build them from sources
• Information that helps finding their calculator popping feature

Table of Contents

1. Engines
   • Overview
   • Chromium
   • Firefox
   • Safari
   • Edge
2. Exploitation
   • Overview
   • Chromium
   • Firefox
   • Safari
   • Edge
3. Tools
4. JavaScript Docs

Engines

Engine-Overview

• Javascript Engine Fundamentals: the good, the bad, and the ugly
• Javascript Engine Fundamentals: Shapes and Inline Caches
• JavaScript Engines - how do they even (Video)

Browse the Sources

Of course you can use you're own favorite setup to browse the sources. However, those repos are relatively large and I tried a couple different setups until I found something that worked for me. So if you don't have good setup already, here are a couple of my experiences that might help you:

• CTags (+Vim): Works well with following references and calls. If you're used to navigate through large source-trees with this puristic setup, it can be a good option for you. The downside being of course the lack of the features most of the big IDEs come with nowadays.
• CLion: I use JetBrain products for a lot of my coding activities, but CLion didn't work well for me, especially following references. Of course this might be due to setup issues.
• Eclipse: I haven't used it in a while, but this turned out to be a good option. Unfortunately, it takes a lot of resources for the indexer to run through the code.
  • Here is a setup description for the Chromium-Project, but it works similarly for the other projects as well.
• ccls+VSCode This is the best option for me so far. ccls is very fast with indexing the repos and works great with VSCode. You can also combine it with other editors and IDEs see https://github.com/MaskRay/ccls/wiki/Editor-Configuration

Chromium (Blink)

Project | GitHub

Articles:

• What is Chromium? (DE)

The JavaScript-Engine of Blink is V8.

V8

Project | GitHub | Source | How2Build

Build (Ubuntu 18.04):

$ git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git
$ export PATH=$PATH:./depot_tools
$ gclient
$ mkdir ./v8 && cd ./v8
$ fetch v8 && cd v8
$ git pull
$ gclient sync
$ ./build/install-build-deps.sh
$ tools/dev/gm.py x64.release
$ out/x64.release/d8

Useful flags:

• --print-opt-code: code generated by optimizing compiler
• --print-byte-code: bytecode generated by interpreter
• --trace-ic: different object types a call site encouters
• --trace-opt and --trace-deopt: which functions are (de)optimized
• --trace-turbo: TurboFan traces for the Turbolizer visualization

Articles:

• A tour of V8

JIT-Compiler: TurboFan

Docs | Blog

V8 provides a visualization for TurboFan called Turbolizer

Articles:

• Introduction to TurboFan

Turbolizer usage:

1. Run v8 with --trace-turbo: d8 --trace-turbo foo.js
2. Generates json files e.g. turbo-foo-0.json
3. Goto v8/tools/turbolizer and install with npm as described in README.md
4. Serve directory e.g. python -m SimpleHTTPServer 8000
5. Browse to localhost:8000 and open turbo-foo-0.json

Firefox (Gecko)

Project | GitHub

The JavaScript-Engine of Gecko is Spidermonkey.

Spidermonkey

Project | Source | How2Build

Source

• builtin

Build (Ubuntu 18.04):

$ wget -O bootstrap.py https://hg.mozilla.org/mozilla-central/raw-file/default/python/mozboot/bin/bootstrap.py && python bootstrap.py
$ git clone https://github.com/mozilla/gecko-dev.git && cd gecko-dev
$ cd js/src
$ autoconf2.13

# This name should end with "_DBG.OBJ" to make the version control system ignore it.
$ mkdir build_DBG.OBJ
$ cd build_DBG.OBJ
$ ../configure --enable-debug --disable-optimize
# Use "mozmake" on Windows
$ make -j 6
$ js/src/js

JIT-Compiler: IonMonkey

Project

Spidermonkey provides a visualization for IonMonkey called IonGraph

Source

• jit

Safari (Webkit)

Project | GitHub

The JavaScript-Engine of Webkit is JavaScriptCore (JSC).

JavaScriptCore

Project | Wiki | Source

Articles:

• http://www.filpizlo.com/papers.html

Source

• Runtime: Source/JavaScriptCore/runtime

Build (Ubuntu 18.04):

# sudo apt install libicu-dev python ruby bison flex cmake build-essential ninja-build git gperf
$ git clone git://git.webkit.org/WebKit.git && cd WebKit
$ Tools/gtk/install-dependencies
$ Tools/Scripts/build-webkit --jsc-only --debug
$ cd WebKitBuild/Release
$ LD_LIBRARY_PATH=./lib bin/jsc

JIT-Compiler: LLInt+ Baseline JIT + DFG JIT + FTL JIT

WebKit has a 4-Layer JIT-Compiler system, representing the tradeoff between overhead performance cost and performance benefit.

Articles:

• Introduction to Webkit's JavaScript JIT Optimizations
• Introducing the B3 JIT Compiler

Source

• LLInt (Low Level Interpreter)
• Baseline JIT
• DFG JIT (Data Flow Graph JIT)
• FTL JIT (Faster Than Light Just In Time compiler)

Edge (Blink/EdgeHTML)

Project | GitHub

Since Edge switched to Blink and the Chromium Project as its Rendering-Engine, Edge is using v8. Originally, Edge had is own Rendering-Engine called EdgeHTML, which used the ChakraCore JavaScript-Engine.

ChakraCore

GitHub | How2Build

Docs

• Architecture Overview

Source

• Runtime: Types
• Runtime: Language

Build (Ubuntu 18.04):

# To build ChakraCore on Linux: (requires Clang 3.7+ and Python 2)
$ apt-get install -y git build-essential cmake clang libicu-dev libunwind8-dev
$ git clone https://github.com/Microsoft/ChakraCore && cd ChakraCore
$ ./build.sh --cc=/usr/bin/clang-3.9 --cxx=/usr/bin/clang++-3.9 --arch=amd64 --debug
$ out/Debug/ch

Exploitation

Exploitation-Overview

• Saelo: Attacking JavaScript-Engines
• Awesome-Browser-Exploitation
• Attacking WebKit applications (Slides)
• Saelo: Attacking Client-Side JIT Compilers - BlackHat 2018
  • Video
  • Slides
• j0nathanj: From Zero to ZeroDay (Finding a Chakra Zero Day)
  • Video Slides
• Saelo: Fuzzili - (Guided-)fuzzing for JavaScript engines
  • Video
  • Slides

Chromium Pwn

Articles

• Exploiting TurboFan Through Bounds Check Elimination
• saelo: Exploiting Logic Bugs in JavaScript JIT Engines
  • Phrack Article
  • 41con 19' slides

CTF-Challenges

• 34c3: v9
  • Sources
  • WriteUp (Exploit-Script)
• 35c3: Krautflare
  • Files
  • WriteUp
  • WriteUp
• CSAW-Finals-2018: ES1337
  • Files+WriteUp
• Plaid CTF 2018: Roll a dice
  • Files
  • WriteUp
  • WriteUp
• Google CTF Finals 2018: Just In Time
  • Files+WriteUp
  • Slides
  • WriteUp
• *CTF 2019: oob-v8
  • Files
  • WriteUp
  • WriteUp
  • WriteUp
• RealWorldCTF Quals 2019: accessible
  • Files
  • WriteUp

RealWorld

• MobilePwn2Own 2013 - Chrome on Android
• https://halbecaf.com/2017/05/24/exploiting-a-v8-oob-write/
• niklasb: Chrome IPC Exploitation
  • Video
  • Slides
• CVE-2019-5782 Write-Up
• CVE-2019-5790
• CVE-2019-5786 Chrome Remote Code Execution Vulnerability Analysis

Hardening & Mitigations

• Heap-hardening

Firefox Pwn

Articles

• Playing around with SpiderMonkey
• OR'LYEH? The Shadow over Firefox
• A journey into IonMonkey: root-causing CVE-2019-9810

CTF-Challenges

• 33c3: Feuerfuchs
  • Sources
  • WriteUp
  • WriteUp+Build
• Blaze 2018: blazefox
  • Sources
  • WriteUp
  • WriteUp (Exploit-Script)
  • WriteUp (Exploit-Script)
  • Build+WriteUp
• 35c3 FunFox
  • Sources

RealWorld

• Introduction to SpiderMonkey exploitation
  • Article
• Use-after-free in Spidermonkey (Beta 53)
  • Article
  • Talk
  • Slides
• https://saelo.github.io/posts/firefox-script-loader-overflow.html
• Use-after-free in SpiderMonkey (64.0a1)
  • Article
• CVE-2019-11707 Type Confusion
  • WriteUp
  • Report
• CVE-2019-11708 & CVE-2019-9810
  • WriteUp

Safari Pwn

CTF-Challenges

• RealWorldCTF 2018: Engine for Neophytes
  • Files
• 35c3: WebKid
  • Sources
  • WriteUp

RealWorld

• http://www.phrack.org/papers/attacking_javascript_engines.html
  • Source
  • WriteUp+Build
• Fuzzing Webkit and analysis of CVE-2019-8375
• CVE-2017-2446 WriteUp
• https://saelo.github.io/posts/jsc-typedarray.slice-infoleak.html
• https://github.com/saelo/pwn2own2018/tree/master/stage0
• https://github.com/LinusHenze/WebKit-RegEx-Exploit
• https://github.com/W00dL3cs/exploit_playground/tree/master/JavaScriptCore

Hardening & Mitigations

• Heap-hardening
• CagedPtr Source & ArrayBuffer Example

Edge

Articles

• bkth: Tale of Chakra Bugs
• bkth: Attacking Edge Through the JavaScript-Compiler
  • Video
  • Slides

CTF-Challenges

• Plaid 2017: chakrazy
  • WriteUp
• N1CTF 2018: Chakra
  • Files
• RealWorldCTF Quals 2019: Appetizer
  • Files
• Trend Micro CTF 2019: ChakraCore 400
  • WriteUp
  • WriteUp
  • Exploit

RealWorld

• bkth, S0rryMyBad: Non JIT Bug, JIT Exploit

Tools

Libraries:

• pwnjs (A Javascript library for browser exploitation)

Utils

• int64.js
• utils.js

Debugging

• shadow jemalloc heap exploitation framework (heap allocator used by Firefox)

JavaScript (ECMAScript) Docs

• Types&Values
• Objects
• Object-Properties