mccr8

Writing Chromium entirely in Rust wouldn't prevent a JIT bug like this.

While working on Firefox, I do sometimes look back at Bugzilla (the project's issue tracker) activity from 26 years ago to try to figure out why some code is the way it is. However it feels hard to believe that the role of LLMs in another 20 years will be close enough to the way it is now for a session history like this to be very useful.

AI is very good at finding security bugs. If you are working on a product that processes hostile data like a web browser and has a security bug bounty program, your choices are either to find them yourself or be overwhelmed by external submissions.

The cute thing about asm.js is that it was fully backwards compatible with the web: it was just a lot slower without dedicated support. So Epic or whomever could put out a demo that would run just fine in Chrome, but the performance was a lot worse than Firefox which had a dedicated compilation pipeline, so it made Chrome look bad.

One of the big issues with NaCl is that the API it used wasn't standardized at all and there was only a single implementation. You could pick a random function and ask "hey, what happens if you pass in some slightly weird arguments?" and there was no answer beyond "whatever Chrome does". With enough work, maybe that could have been overcome while preserving backwards compatibility, but there were lots of random functions in there because somebody or other had found it useful. WASM was built from the ground up with a standards process and multiple implementations.

Fuzzing isn't good at things like dealing with code behind a CRC check, whereas the audit based approach using an LLMs can see the sketchy code, then calculate the CRC itself to come up with a test case. I think you end up having to write custom fuzzing harnesses to get at the vulnerable parts of the code. (This is an example from a talk by somebody at Anthropic.)

That being said, I think there's a lot of potential for synergy here: if LLMs make writing code easier, that includes fuzzers, so maybe fuzzers will also end up finding a lot more bugs. I saw somebody on Twitter say they used an LLM to write a fuzzer for Chrome and found a number of security bugs that they reported.

Mostly I think this just means that having a test case makes it easier to fix and verify. You can't actually take for granted having a test case when fixing a security bug. Sometimes you only have a crash stack or maybe a vague and hypothetical static analysis result.

> eventually land the test case

This is just a reference to the fact that we don't land test cases for security bugs immediately in the public repository, to make it harder for attackers. You are right that the LLM only helps with creating the initial test case. Things like running the test case in automation is part of the standard development process.

A general limitation of this approach is that it is only as good as your validator, and there's nothing easier to validate than a test case that creates, say, an AddressSanitizer use-after-free. For subtler issues will we have to more specific validators or will the LLM become better at coming up with other dangerous conditions it will verify? We'll see.

Firefox developers do fix issues found by Coverity. I haven't looked at the results in over a decade, but the last time I did there were a few code patterns we used in a lot of places which Coverity didn't like (but were actually okay the way we were doing them) which resulted in a colossal number of false positives.

Possibly! One of the many areas that might need rethinking in the age of AI (that started in February of this year) is how long security bugs should be hidden. We live in interesting times.

I'd say it leans towards memory corruption kinds of issues, as those are easiest to pass the validator, thanks to AddressSanitizer. I think there's a lot of potential for making the validator more sophisticated. Like maybe you add a JS function that will only crash when run in the parent process and have a validator that checks for that specific crash, as a way for the LLM to "prove" that it managed to run arbitrary JS in the parent. Would that turn up subtler issues? Maybe.

Quantifying the abilities of an LLM is a hard research problem, so I'm not sure if I can describe it in any great way, but Mythos did seem to be fairly clever about putting together things from different domains to find problems.

For instance, in one of the included bugs (2022034) it figured out that a floating point value being sent over IPC could be modified by an attacker in such a way that it would be interpreted by the JS engine as an arbitrary pointer, due to the way the JS engine uses a clever representation of values called NaN-boxing. This is not beyond the realm of a human researcher to find, but it did nicely combine different domains of security.

As the person responsible for accidentally introducing that security problem (and then fixing it after the Mythos report), while I am aware of NaN-boxing (despite not being a JS engine expert), I was focused more on the other more complex parts of this IPC deserialization code so I hadn't really thought about the potential problems in this context. It is just a floating point value, what could go wrong?