GHSA-6845-xw22-ffxv

Описание

Summary

There is an error in the stack management when compiling the IR for sha3_64. Concretely, the height variable is miscalculated. The vulnerability can't be triggered without writing the IR by hand. That is, it cannot be triggered from regular vyper code, it can only be triggered by using the fang binary directly (this binary used to be called vyper-ir prior to v0.3.4).

Details

To compile sha3_64, the arg[0] and arg[1] have to be compiled: https://github.com/vyperlang/vyper/blob/c150fc49ee9375a930d177044559b83cb95f7963/vyper/ir/compile_ir.py#L585-L586

As can be seen, after compiling the 0th arg, the height variable isn't increased. If new withargs are defined in the inner scope, they are manipulated correctly, because both their height is off and also the global height is off and thus their placement on the stack is computed correctly.

sha3_64 is used for retrieval in mappings. No flow that would cache the key was found, the issue shouldn't be possible to trigger when compiling the compiler-generated IR.

PoC

Suppose the following hand-written IR:

after compilation:

It can be seen that the second DUP will dup the item on the top of the stack which is incorrect.

Patches

Patched in https://github.com/vyperlang/vyper/pull/4063.

Impact

Versions v0.2.0-v0.3.10 were evaluated, and access of the variable with the invalid height is not reachable from IR generated by the vyper front-end. Because the issue isn't triggered during normal compilation of vyper code, the impact is considered low.