What’s Vulnerable › Vulnerabilities

CVE-2021-41264: UUPSUpgradeable vulnerability in OpenZeppelin Contracts

• Severity: high (CVSS 7.5 v2.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-11-12 · updated 2026-06-17
• Weakness: CWE-665

Description

OpenZeppelin Contracts is a library for smart contract development. In affected versions upgradeable contracts using `UUPSUpgradeable` may be vulnerable to an attack affecting uninitialized implementation contracts. A fix is included in version 4.3.2 of `@openzeppelin/contracts` and `@openzeppelin/contracts-upgradeable`. For users unable to upgrade; initialize implementation contracts using `UUPSUpgradeable` by invoking the initializer function (usually called `initialize`). An example is provided [in the forum](https://forum.openzeppelin.com/t/security-advisory-initialize-uups-implementation-contracts/15301).

Affected products

• openzeppelin-contracts: from 4.1.0 before 4.3.2 — fixed in 4.3.2

How to fix

Upgrade to a fixed version: openzeppelin-contracts 4.3.2. Check the vendor advisory for mitigations.

References

• https://forum.openzeppelin.com/t/security-advisory-initialize-uups-implementation-contracts/15301
• https://github.com/OpenZeppelin/openzeppelin-contracts/commit/024cc50df478d2e8f78539819749e94d6df60592
• https://github.com/OpenZeppelin/openzeppelin-contracts/security/advisories/GHSA-5vp3-v4hc-gx76
• https://forum.openzeppelin.com/t/security-advisory-initialize-uups-implementation-contracts/15301
• https://github.com/OpenZeppelin/openzeppelin-contracts/commit/024cc50df478d2e8f78539819749e94d6df60592
• https://github.com/OpenZeppelin/openzeppelin-contracts/security/advisories/GHSA-5vp3-v4hc-gx76

Get alerted when CVE-2021-41264 or the next vulnerability affects your stack