Incorrect success value returned in vyper
Background
During the audit of Lido's Gate Seals code statemind 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:
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.
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 stackImpact
Example of buggy code:
@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
Software afectado
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| Plataforma | Paquete | Versiones vulnerables | Corregida en |
|---|---|---|---|
| Python (PyPI) | vyper | >= 0.3.1, < 0.3.8 | 0.3.8 |
Referencias
- https://docs.vyperlang.org/en/v0.3.7/built-in-functions.html#raw_call
- https://github.com/lidofinance/gate-seals/pull/5/files
- https://github.com/lidofinance/gate-seals/blob/051593e74df01a4131c485b4fda52e691cd4b7d8/contracts/GateSeal.vy#L164
- https://github.com/vyperlang/vyper/security/advisories/GHSA-w9g2-3w7p-72g9
- https://github.com/vyperlang/vyper/commit/851f7a1b3aa2a36fd041e3d0ed38f9355a58c8ae
- https://nvd.nist.gov/vuln/detail/CVE-2023-30629
- https://github.com/pypa/advisory-database/tree/main/vulns/vyper/PYSEC-2023-131.yaml
- https://github.com/vyperlang/vyper
- Vector CVSS
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N- Debilidad (CWE)
CWE-670- Plataforma
- Python (PyPI)
- Paquete
vyper- Publicada
- 24.04.2023
- Actualizado
- 11.10.2026 15:17
Fuentes y licencias
OSV / GitHub Advisory Database - PYSEC-2023-131 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-w9g2-3w7p-72g9 - CC BY 4.0
Historial de vulnerabilidades: vyper
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