---
id: CVE-2023-30629
aliases:
  - GHSA-w9g2-3w7p-72g9
  - PYSEC-2023-131
title: Incorrect success value returned in vyper
summary: Incorrect success value returned in vyper
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N'
vendor: vyper
product: vyper
ecosystem: pip
affected:
  - 'vyper >= 0.3.1, < 0.3.8'
patched:
  - vyper 0.3.8
published: '2023-04-24'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T03:50:01.176366652Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-w9g2-3w7p-72g9'
references:
  - url: 'https://github.com/vyperlang/vyper/security/advisories/GHSA-w9g2-3w7p-72g9'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2023-30629'
  - url: 'https://github.com/lidofinance/gate-seals/pull/5/files'
  - url: >-
      https://github.com/vyperlang/vyper/commit/851f7a1b3aa2a36fd041e3d0ed38f9355a58c8ae
  - url: 'https://docs.vyperlang.org/en/v0.3.7/built-in-functions.html#raw_call'
  - url: >-
      https://github.com/lidofinance/gate-seals/blob/051593e74df01a4131c485b4fda52e691cd4b7d8/contracts/GateSeal.vy#L164
  - url: >-
      https://github.com/pypa/advisory-database/tree/main/vulns/vyper/PYSEC-2023-131.yaml
  - url: 'https://github.com/vyperlang/vyper'
tags:
  - osv
  - pip
epss: 0.00883
epssPercentile: 0.57478
ingestedAt: '2026-09-12T03:13:01.734Z'
---

## Overview

### 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

- `vyper >= 0.3.1, < 0.3.8`

## Remediation

Upgrade to a patched release:

- `vyper 0.3.8`