Summary
VVE-2021-0002: Incorrect returndatasize when using simple forwarder proxies deployed prior to EIP-1167 adoption
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.
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.
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.
The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
The issue was patched when we upgraded to EIP-1167 style forwarder proxies in #2281.
Frequently Asked Questions
- What is GHSA-375M-5FVV-XQ23? GHSA-375M-5FVV-XQ23 is a low-severity improper input validation vulnerability in vyper (pip), affecting versions < 0.2.9. It is fixed in 0.2.9. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
- Which versions of vyper are affected by GHSA-375M-5FVV-XQ23? vyper (pip) versions < 0.2.9 is affected.
- Is there a fix for GHSA-375M-5FVV-XQ23? Yes. GHSA-375M-5FVV-XQ23 is fixed in 0.2.9. Upgrade to this version or later.
- Is GHSA-375M-5FVV-XQ23 exploitable, and should I be worried? Whether GHSA-375M-5FVV-XQ23 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether GHSA-375M-5FVV-XQ23 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix GHSA-375M-5FVV-XQ23? Upgrade
vyperto 0.2.9 or later.