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Critical, CVSS 9.8amended

UUPSUpgradeable vulnerability in @openzeppelin/contracts

CVE-2021-41264GHSA-5vp3-v4hc-gx76

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (@openzeppelin/contracts 4.3.2; @openzeppelin/contracts-upgradeable 4.3.2), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
9.8 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS
  • CVE-2021-41264: 1.49% estimated exploitation activity in the next 30 days; percentile 74.08 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

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 security@openzeppelin.com.

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-5vp3-v4hc-gx76

  2. Revision 1 · created ·

    Published from osv record GHSA-5vp3-v4hc-gx76

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2021-41264

Advisory: UUPSUpgradeable vulnerability in @openzeppelin/contracts
IDs: CVE-2021-41264, GHSA-5vp3-v4hc-gx76
Record: https://patchnext.com/advisories/cve-2021-41264 (revision 2, source checked 26 Oct 2026, 12:16 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @openzeppelin/contracts 4.3.2; @openzeppelin/contracts-upgradeable 4.3.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @openzeppelin/contracts: affected >= 4.1.0, < 4.3.2; fixed in 4.3.2
- npm @openzeppelin/contracts-upgradeable: affected >= 4.1.0, < 4.3.2; fixed in 4.3.2

## Suggested inspection (read-only)
- `npm ls @openzeppelin/contracts --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.
- `npm ls @openzeppelin/contracts-upgradeable --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @openzeppelin/contracts, @openzeppelin/contracts-upgradeable.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-5vp3-v4hc-gx76 (OSV record GHSA-5vp3-v4hc-gx76 lists affected ranges: npm @openzeppelin/contracts >=4.1.0 =4.1.0 <4.3.2 (fixed))
- Verified: https://github.com/advisories/GHSA-5vp3-v4hc-gx76 (GitHub-reviewed advisory GHSA-5vp3-v4hc-gx76 lists affected ranges: npm @openzeppelin/contracts >=4.1.0 =4.1.0 <4.3.2)

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