What is CVE-2021-41264?

CVE-2021-41264 is a critical-severity vulnerability in Openzeppelin Contracts, classified under Improper Initialization. CVSS score: 9.8/10. Published 2021-11-12.

How severe is CVE-2021-41264?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Is CVE-2021-41264 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Vulnerability in Openzeppelin Contracts

CVE-2021-41264

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).

Vulnerability class: Dirty Pipe (CVE-2022-0847)

Published 2021-11-12 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.015 (73.0th percentile), scored 2026-09-29.

Low probability of exploitation in the next 30 days, but still tracked. 73rd percentile — 73.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.014 · newest: 0.015 · change: +0.000

Affected products

Openzeppelin Contracts
Openzeppelin Openzeppelin-Contracts — versions >= 4.1.0 < 4.3.2

Weakness classification (CWE)

CWE-665 — Improper Initialization

Public proof-of-concept exploits

chloegeo/sc

References

github.com/OpenZeppelin/openzeppelin-contracts/security/advisories/GHSA-5vp3-v4… (Third Party Advisory)
github.com/OpenZeppelin/openzeppelin-contracts/commit/024cc50df478d2e8f78539819… (Patch, Third Party Advisory)
forum.openzeppelin.com/t/security-advisory-initialize-uups-implementation-contr… (Patch, Mitigation, Issue Tracking, Vendor Advisory)

Frequently asked questions

What is CVE-2021-41264?: CVE-2021-41264 is a critical-severity vulnerability in Openzeppelin Contracts, classified under Improper Initialization. CVSS score: 9.8/10. Published 2021-11-12.
How severe is CVE-2021-41264?: Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2021-41264 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.