CVE-2021-41264 is a critical-severity (CVSS 9.8) CWE-665 vulnerability in @openzeppelin/contracts. O3 Security confirms whether CVE-2021-41264 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
UUPSUpgradeable vulnerability in @openzeppelin/contracts
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, a proxy for how much of the ecosystem is exposed.
@openzeppelin/contractsnpm@openzeppelin/contracts-upgradeablenpmDescription
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @openzeppelin/contracts | ≥ 4.1.0&&< 4.3.2 | 4.3.2 |
| 📦npm | @openzeppelin/contracts-upgradeable | ≥ 4.1.0&&< 4.3.2 | 4.3.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @openzeppelin/contracts. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
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.
How O3 protects you
O3 pinpoints whether CVE-2021-41264 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2021-41264. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2021-41264 in your dependencies?
O3 detects CVE-2021-41264 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.