You can imagine a pipeline that looks at individual source files or functions. And first "extracts" what is going on. You ask the model:
- "Is the code doing arithmetic in this file/function?" - "Is the code allocating and freeing memory in this file/function?" - "Is the code the code doing X/Y/Z? etc etc"
For each question, you design the follow-up vulnerability searchers.
For a function you see doing arithmetic, you ask:
- "Does this code look like integer overflow could take place?",
For memory:
- "Do all the pointers end up being freed?" _or_ - "Do all pointers only get freed once?"
I think that's the harness part in terms of generating the "bug reports". From there on, you'll need a bunch of tools for the model to interact with the code. I'd imagine you'll want to build a harness/template for the file/code/function to be loaded into, and executed under ASAN.
If you have an agent that thinks it found a bug: "Yes file xyz looks like it could have integer overflow in function abc at line 123, because...", you force another agent to load it in the harness under ASAN and call it. If ASAN reports a bug, great, you can move the bug to the next stage, some sort of taint analysis or reach-ability analysis.
So at this point you're running a pipeline to: 1) Extract "what this code does" at the file, function or even line level. 2) Put code you suspect of being vulnerable in a harness to verify agent output. 3) Put code you confirmed is vulnerable into a queue to perform taint analysis on, to see if it can be reached by attackers.
Traditionally, I guess a fuzzer approached this from 3 -> 2, and there was no "stage 1". Because LLMs "understand" code, you can invert this system, and work if up from "understanding", i.e. approach it from the other side. You ask, given this code, is there a bug, and if so can we reach it?, instead of asking: given this public interface and a bunch of data we can stuff in it, does something happen we consider exploitable?
I think there is already papers and presentations on integrating these kind of iterative code understanding/verificaiton loops in harnesses. There may be some advantages over fuzzing alone. But I think the cost-benefit analysis is a lot more mixed/complex than anthropic would like people to believe. Sure you need human engineers but it's not like insurmountably hard for a non-expert to figure out
That's funny, this is how I've been doing security testing in my code for a while now, minus the 'taint analysis'. Who knew I was ahead of the game. :P
In all seriousness though, it scares me that a lot of security-focused people seemingly haven't learned how LLMs work best for this stuff already.
You should always be breaking your code down into testable chunks, with sets of directions about how to chunk them and what to do with those chunks. Anyone just vaguely gesturing at their entire repo going, "find the security vulns" is not a serious dev/tester; we wouldn't accept that approach in manual secure coding processes/ SSDLCs.
In a large codebase there will still be bugs in how these components interoperate with each other, bugs involving complex chaining of api logic or a temporal element. These are the kind of bugs fuzzers generally struggle at finding. I would be a little freaked out if LLMs started to get good at finding these. Everything I've seen so far seems similar to fuzzer finds.