Vyper is a Pythonic Smart Contract Language for the EVM. The `_abi_decode()` function does not validate input when it is nested in an expression. Uses of `_abi_decode()` can be constructed which allow for bounds checking to be bypassed resulting in incorrect results. This issue has not yet been fixed, but a fix is expected in release `0.3.10`. Users are advised to reference pull request #3626.

Affected: PyPI: vyper

### Impact `_abi_decode()` does not validate input when it is nested in an expression. the following example gets correctly validated (bounds checked): ```vyper x: int128 = _abi_decode(slice(msg.data, 4, 32), int128) ```

however, the following example is not bounds checked ```vyper @external def abi_decode(x: uint256) -> uint256: a: uint256 = convert(_abi_decode(slice(msg.data, 4, 32), (uint8)), uint256) + 1 return a # abi_decode(256) returns: 257 ```

the issue can be triggered by constructing an example where the output of `_abi_decode` is not internally passed to `make_setter` (an internal codegen routine) or other input validating routine.

### Patches https://github.com/vyperlang/vyper/pull/3626

### Workarounds _Is there a way for users to fix or remediate the vulnerability without upgrading?_

### References _Are there any links users can visit to find out more?_

Affected: PyPI: vyper

Vyper is a Pythonic Smart Contract Language for the EVM. The `_abi_decode()` function does not validate input when it is nested in an expression. Uses of `_abi_decode()` can be constructed which allow for bounds checking to be bypassed resulting in incorrect results. This issue has not yet been fixed, but a fix is expected in release `0.3.10`. Users are advised to reference pull request #3626.