GHSA-6845-xw22-ffxv
GitHub Security Advisory
Vyper sha3 codegen bug
Advisory Details
### 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:
```lisp
(with _loc
(with val 1
(with key 2
(sha3_64 val key)))
(seq
(sstore _loc
(with x (sload _loc)
(with ans (add x 1) (seq (assert (ge ans x)) ans))))))
```
after compilation:
```
the generated bytecode: 6001600281806020525f5260405f2090509050805460018101818110610026579050815550005b5f80fd
0000 60 PUSH1 0x01
0002 60 PUSH1 0x02
0004 81 DUP2
0005 80 DUP1 *********** bad code here!!!!!!
0006 60 PUSH1 0x20
0008 52 MSTORE
```
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.
Affected Packages
Related CVEs
Key Information
Dataset
Data from GitHub Advisory Database. This information is provided for research and educational purposes.