CVE-2023-40014: OpenZeppelin Contracts's ERC2771Context with custom forwarder may lead to zero-valued _msgSender

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.7% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2023-08-10 · updated 2026-06-17
Weakness: CWE-116

Description

OpenZeppelin Contracts is a library for secure smart contract development. Starting in version 4.0.0 and prior to version 4.9.3, contracts using `ERC2771Context` along with a custom trusted forwarder may see `_msgSender` return `address(0)` in calls that originate from the forwarder with calldata shorter than 20 bytes. This combination of circumstances does not appear to be common, in particular it is not the case for `MinimalForwarder` from OpenZeppelin Contracts, or any deployed forwarder the team is aware of, given that the signer address is appended to all calls that originate from these forwarders. The problem has been patched in v4.9.3.

Affected products

Openzeppelin Contracts: from 4.0.0 before 4.9.3 — fixed in 4.9.3
Openzeppelin Contracts-Upgradable: from 4.0.0 before 4.9.3 — fixed in 4.9.3

How to fix

Upgrade to a fixed version: Openzeppelin Contracts 4.9.3; Openzeppelin Contracts-Upgradable 4.9.3. Check the vendor advisory for mitigations.

References

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