Vyper is a Pythonic Smart Contract Language for the Ethereum Virtual Machine. The `concat` built-in can write over the bounds of the memory buffer that was allocated for it and thus overwrite existing valid data. The root cause is that the `build_IR` for `concat` doesn't properly adhere to the API of copy functions (for `>=0.3.2` the `copy_bytes` function). A contract search was performed and no vulnerable contracts were found in production. The buffer overflow can result in the change of semantics of the contract. The overflow is length-dependent and thus it might go unnoticed during contract testing. However, certainly not all usages of concat will result in overwritten valid data as we require it to be in an internal function and close to the return statement where other memory allocations don't occur. This issue has been addressed in 0.4.0.
The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer, leading to a buffer overflow.
The product writes data past the end, or before the beginning, of the intended buffer.
| Link | Tags |
|---|---|
| https://github.com/vyperlang/vyper/security/advisories/GHSA-2q8v-3gqq-4f8p | vendor advisory exploit |
| https://github.com/vyperlang/vyper/issues/3737 | vendor advisory issue tracking exploit |
| https://github.com/vyperlang/vyper/commit/55e18f6d128b2da8986adbbcccf1cd59a4b9ad6f | patch |