How severe is CVE-2021-41264?

CVE-2021-41264 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-41264?

CVE-2021-41264 affects the following packages: @openzeppelin/contracts (npm), @openzeppelin/contracts-upgradeable (npm). Ecosystems affected: npm.

How do I fix CVE-2021-41264?

Update @openzeppelin/contracts to 4.3.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-41264 is resolved across your whole dependency graph.

How do I detect CVE-2021-41264 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @openzeppelin/contracts, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-41264 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2021-41264 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-41264 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2021-41264?

CVE-2021-41264 has an EPSS (Exploit Prediction Scoring System) score of 1.5%, placing it in the 73th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-41264?

CVE-2021-41264 is classified as CWE-665 (CWE-665). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-41264 published, and has it been updated?

CVE-2021-41264 was published on November 12, 2021 and was last updated on July 22, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦

📦 npm

Not in CISA KEV

CRITICAL severity

CVE-2021-41264 — @openzeppelin/contracts

CRITICALFix: OpenZeppelin/openzeppelin-contracts@024cc50

CVE-2021-41264 is a critical-severity (CVSS 9.8) CWE-665 vulnerability in @openzeppelin/contracts. A fix is available for @openzeppelin/contracts — see the affected versions and patch details below.

UUPSUpgradeable vulnerability in @openzeppelin/contracts

Also known asGHSA-5vp3-v4hc-gx76

Published

Nov 12, 2021

Updated

Jul 22, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Oct 13, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

1.5%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs73th percentile — riskier than 73% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-41264 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,987 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

2 pkgs affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

4Kother npm packages depend on this — each one inherits the vulnerability until it's patched upstream

@openzeppelin/contractsnpm

929Kdownloads / week

@openzeppelin/contracts-upgradeablenpm

251Kdownloads / week

Description

Impact

Upgradeable contracts using UUPSUpgradeable may be vulnerable to an attack affecting uninitialized implementation contracts. We will update this advisory with more information soon.

Patches

A fix is included in version 4.3.2 of @openzeppelin/contracts and @openzeppelin/contracts-upgradeable.

Workarounds

Initialize implementation contracts using UUPSUpgradeable by invoking the initializer function (usually called initialize). An example is provided in the forum.

References

Post-mortem.

For more information

If you have any questions or comments about this advisory, or need assistance executing the mitigation, email us at [email protected].

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`@openzeppelin/contracts`	≥ 4.1.0&&< 4.3.2	4.3.2`npm install @openzeppelin/contracts@4.3.2`
📦npm	`@openzeppelin/contracts-upgradeable`	≥ 4.1.0&&< 4.3.2	4.3.2`npm install @openzeppelin/contracts-upgradeable@4.3.2`

Affected Products

1 product · 1 configurations

Application

contractsopenzeppelin

≥ 4.1.0 && < 4.3.2

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @openzeppelin/contracts, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update @openzeppelin/contracts to 4.3.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-41264 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

### Impact Upgradeable contracts using `UUPSUpgradeable` may be vulnerable to an attack affecting uninitialized implementation contracts. We will update this advisory with more information soon. ### Patches A fix is included in version 4.3.2 of `@openzeppelin/contracts` and `@openzeppelin/contracts-upgradeable`. ### Workarounds 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).