Vulnerability · Published Oct 21, 2026 · Assigned by VulnCheck

CVE-2021-48019Vyper before 0.2.9 Incorrect RETURNDATASIZE in create_forwarder_to Proxies

Medium 4.8

In plain English

A medium-severity security flaw in vyper from vyperlang. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 16% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)4.8Medium

Exploit odds (30 days)0.2%top 83.9% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

Vyper before 0.2.9 deploys forwarder proxies through the built-in create_forwarder_to function that report a fixed 4096-byte RETURNDATASIZE rather than the actual return data size. Calls through these proxies can yield corrupted data when a function returns more than 4096 bytes without return data sanitation, and fail strict return-size checks such as SafeERC20.safeTransfer.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
PyPI	vyper	0.2.9	GHSA-375m-5fvv-xq23

Affected products (as reported)

Vendor	Product	Versions
vyperlang	vyper	0 – before 0.2.9

Weakness: CWE-805 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L

References

GitHub Security Advisory (GHSA-375m-5fvv-xq23) vendor-advisory
VulnCheck Advisory: Vyper before 0.2.9 Incorrect RETURNDATASIZE in create_forwarder_to Proxies third-party-advisory