vyper default functions don't respect nonreentrancy keysGHSA-m2v9-w374-5hj9
MEDIUMFix: vyperlang/vyper@93287e5GHSA-m2v9-w374-5hj9 is a medium-severity (CVSS 5.3) CWE-667 vulnerability in vyper. A fix is available for vyper — see the affected versions and patch details below.
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-m2v9-w374-5hj9.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
vyperReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Summary
Prior to v0.3.0, __default__() functions did not respect the @nonreentrancy decorator and the lock was not emitted. This is a known bug and was already visible in the issue tracker (https://github.com/vyperlang/vyper/issues/2455), but it is being re-issued as an advisory so that tools relying on the advisory publication list can incorporate it into their searches.
A contract search was additionally performed and no vulnerable contracts were found in production.
PoC
@external
@payable
@nonreentrant("default")
def __default__():
pass
after codegen:
[seq,
[if, [lt, calldatasize, 4], [goto, fallback]],
[mstore, 28, [calldataload, 0]],
[with, _func_sig, [mload, 0], seq],
[seq_unchecked,
[label, fallback],
[seq,
pass,
# Line 5
pass,
pass,
# Line 4
stop]]],
Impact
No vulnerable production contracts were found. Additionally, using a lock on a default function is a very sparsely used pattern. As such, the impact is low.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | vyper | all versions | 0.3.0pip install --upgrade 'vyper==0.3.0' |
Affected Products
vypervyperlangDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for vyper, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update vyper to 0.3.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-m2v9-w374-5hj9 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is GHSA-m2v9-w374-5hj9 in your dependencies?
Find it across PyPI, including transitive dependencies.