GHSA-375m-5fvv-xq23
Fix: vyperlang/vyper#2281GHSA-375m-5fvv-xq23 is a security vulnerability in vyper. O3 Security confirms whether GHSA-375m-5fvv-xq23 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
VVE-2021-0002: Incorrect `returndatasize` when using simple forwarder proxies deployed prior to EIP-1167 adoption
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
Background
@tjayrush reported a data handling issue with certain Web3 libraries using Vyper-deploy forwarder proxy contracts using our Vyper's built-in create_forwarder_to function prior to our change to support EIP-1167 style forwarder proxies.
Impact
If you are an end user of a forwarder-style proxy deployed using Vyper's built-in create_forwarder_to function AND you have a function that returns >4096 bytes AND you do no return data sanitation on the value returned, you could potentially see a data corruption issue.
Otherwise, if you are handling the result of a return call AND you expect a specific RETURNDATASIZE that is less than 4096 (such as SafeERC20.safeTransfer) then the call will fail that check.
Patches
The issue was patched when we upgraded to EIP-1167 style forwarder proxies in #2281.
Workarounds
If you are making a call to a contract method that is expected to return <= 4096 bytes, there is no issue as the ABI decoders in both Solidity and Vyper will truncate the data properly. Web3 libraries will also do this, unless you are doing eth_call or eth_sendTransaction directly.
If you are using a Solidity library that checks RETURNDATASIZE of an external call to a forwarder proxy deployed prior to this patch, it will fail on that assertion (such as SafeERC20.safeTransfer). The workaround is to always do a greater than or equal to check, rather than a strict equals to check.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | vyper | all versions | 0.2.9 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for vyper. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update vyper to 0.2.9 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-375m-5fvv-xq23 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.
How O3 protects you
O3 pinpoints whether GHSA-375m-5fvv-xq23 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-375m-5fvv-xq23. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-375m-5fvv-xq23 in your dependencies?
O3 detects GHSA-375m-5fvv-xq23 across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.