alt Hacker NewsCan anyone explain how use after free results in a practical exploit?
I ask because I’ve been dabbling in rooting various closed devices at home. I’m finding AI fantastic at finding vulnerabilities statically (from firmware upgrade binaries), but when you then ask it to use it to get root or code execution it just goes in circles.
In the end it usually ends up there’s no exploit it can find, because it can’t actually influence the affected memory in a useful way. This is especially so if that memory is in the heap. On the stack it’s a lot more predictable (especially with OOB writes).
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If it’s freed it can be reallocated, so then you have pointers to the same area of memory used for completely different data structures, and this can go very wrong
One example is that you might be able to read what was written there. Here that may mean you could read another process’s packet(s). Imagine they were sending unencrypted passwords, perhaps because it’s in a trusted LAN connection.
It goes around in circles because a UAF alone isn't enough in a lot of cases, sometimes you also need a chain (an info leak, read/write primitive etc), a way to defeat ASLR and so on depending on what you are working on and target mitigations. Not all UAFs can be used for RCEs, some can be used only for DoS or for nothing really.
been doing exactly this lately with camera firmware and yeah the circles thing is real, but im pretty sure its a feedback loop problem, not a model problem
the model spins because it cant test its own guesses. what fixed it for me was emulating the actual device. qemu with the vendor rootfs, real binaries running, and then every claim becomes checkable: did the daemon actually parse my input, which uid is it under, what does its own log say. once it can check things it stops guessing, getting qemu to actually boot the thing was its own little hell though, took more tries than i want to admit.
the other thing i learned the hard way: most static findings die on reachability, not on exploit primitives. so i run them in the emulator first and kill the unreachable ones cheap, before spending any time on heap work
on heap vs stack, i think that intuition is desktop shaped. device userland usually has weak or no mitigations, heap uafs are way more tractable there than youd expect
You need to do some https://en.wikipedia.org/wiki/Heap_feng_shui. If you can reasonably reliably trigger some other operation that allocated the freed memory for another purpose, you have something like a type confusion vulnerability.