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GHSA-w9g2-3w7p-72g9

GitHub Security Advisory

Incorrect success value returned in vyper

✓ GitHub Reviewed HIGH Has CVE

Advisory Details

### Background
During the audit of [Lido's Gate Seals](https://github.com/lidofinance/gate-seals) code [statemind](https://statemind.io) team identified a weird behavior of the code that uses `raw_call`: https://github.com/lidofinance/gate-seals/blob/051593e74df01a4131c485b4fda52e691cd4b7d8/contracts/GateSeal.vy#L164 .

Construction like this:
```vyper
success = raw_call(
sealable,
_abi_encode(SEAL_DURATION_SECONDS, method_id=method_id("pauseFor(uint256)")),
revert_on_failure=False
)
```
was not fully documented: https://docs.vyperlang.org/en/v0.3.7/built-in-functions.html#raw_call .

The documentation says that: if `max_outsize=0` it should return nothing and then it says that if `revert_on_failure=False` it should return a `success` flag in the tuple of response, but what if `max_outsize=0` and `revert_on_failure=False`.

<img width="715" alt="image" src="https://user-images.githubusercontent.com/22330612/232125364-d2b3bbac-0b4f-40cb-80ff-f55d8eafef44.png">

So the team started researching what exactly happened in that case, after some research we found that the Vyper compiler generates the wrong bytecode in that case, it generates the sequence:
```
CALL // call
MLOAD // MLOAD is wrong since the CALL result is already stored in the stack
```

### Impact
Example of buggy code:
```vyper
@external
def returnSome(calling: address, a: uint256) -> bool:
success: bool = false
success = raw_call(
calling,
_abi_encode(a, method_id=method_id("a(uint256)")),
revert_on_failure=False
)
```

any contract that uses the `raw_call` with `revert_on_failure=False` and `max_outsize=0` receives the wrong response from `raw_call`. Depending on the memory garbage, the result can be either `True` or `False`.

### Patches
Fix by @charles-cooper https://github.com/vyperlang/vyper/commit/851f7a1b3aa2a36fd041e3d0ed38f9355a58c8ae

### Workarounds
The simple workaround is always to put `max_outsize>0`.
Workaround example https://github.com/lidofinance/gate-seals/pull/5/files

### References
Lido's fix: https://github.com/lidofinance/gate-seals/pull/5/files

Affected Packages

PyPI vyper
Affected versions: 0.3.1 (fixed in 0.3.8)

Related CVEs

Key Information

GHSA ID
GHSA-w9g2-3w7p-72g9
Published
April 24, 2023 10:33 PM
Last Modified
November 19, 2024 4:31 PM
CVSS Score
7.5 /10
Primary Ecosystem
PyPI
Primary Package
vyper
GitHub Reviewed
✓ Yes

Dataset

Last updated: June 18, 2025 6:25 AM

Data from GitHub Advisory Database. This information is provided for research and educational purposes.