Contents

Chromium Bug Hunting Adventures 01 - The Big Picture

Motivation

I’ve always had an interest for finding security vulnerabilities in widely-used complex software with a large attack surface. Web browsers seem to be an excellent target for this as they are open source and widely documented. They have an array of components with a complex software architecture. This makes their attack surface quite large. Since there are many browsers, I decided to pick the most widely adopted one - Chromium.

It is worth noting that the developers have taken security quite seriously by adding various countermeasures to protect users from software exploits. Chromium is also open-source, which means that bugs can be found by running and debugging the source code.

While browser exploitation is a scary topic with all of its complexities, I figured that in 2025 it was finally time to take the leap of faith and take a serious stab at hunting for zero-days in Chromium.

Whether I succeed or not, I’m planning on documenting my journey with some of the struggles and challenges of learning the architecture and the art of finding security vulnerabilities in Chromium.

The aim of this blog post is to help consolidate my thoughts, ensuring that Chromium research and bug hunting efforts are optimized for the best use of time while remaining relevant and in-scope.

Understanding the Main Objective

  1. We want to understand what kinds of security bugs Chromium is interested in. As such, it is is critical to review the Chromium Security page.
  2. The Chrome Vulnerability Reward Program suggests a few targets. It is probably best to hunt on the Stable channel and focus on a single in-scope component. This program behaves similar to any other bug bounty hunting program (e.g. don’t report duplicates, exploitation of vulnerability must be reproducible in practice with real impact, etc..).

Prerequisites for reward

To be eligible for the full reward amount in these tables, the issue MUST be:

  • Web accessible, i.e. it can be triggered by remote content.
  • Not mitigated, i.e. does not require user interaction, installing an extension, or being triggered by browser shutdown, or profile destruction.

This is an important starting point for understanding the types of relevant inputs to the program that are worth tracing.

Below are some types of bugs that are in-scope for the chrome vulnerability reward program:

Application Security Architecture

Chromium has developed multiple application security countermeasures, making it more difficult to exploit. Consider learning and reviewing security mechanisms used by Chromium. Generally speaking, a bug in a security mechanism is a security bug.

Parallel Fuzzing

While doing static and dynamic analysis, it can also be helpful to build some automation to find crashes in the program. Google rewards for fuzzers built on top of libFuzzer. https://bughunters.google.com/about/rules/chrome-friends/5745167867576320/chrome-vulnerability-reward-program-rules#chrome-fuzzer-program

If your fuzzer finds a crash, you should be able to claim a bounty for it.

Inspiration from Google Project Zero

I find it handy to review and leverage what other successful researchers have done in the past to get an idea and feel for what to look for, as well as some of the challenges imposed by any security countermeasures we should be expecting. Below are some links to some CVEs that have been found in previous versions of Chromium.

Next Steps

  1. Preparing the Debugging Environment
  2. Become familiar with Chromium’s application architecture
  3. Reproduce a CVE that is modern and up-to-date such as CVE-2025-5419

References