How severe is CVE-2021-39167?

CVE-2021-39167 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-39167?

CVE-2021-39167 affects the following packages: @openzeppelin/contracts (npm), @openzeppelin/contracts (npm). Ecosystems affected: npm.

How do I fix CVE-2021-39167?

Update @openzeppelin/contracts to 4.3.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-39167 is resolved across your whole dependency graph.

How do I detect CVE-2021-39167 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-2021-39167 if there is no patch (or I can't update yet)?

Close the privilege gap rather than the entry point: audit which accounts, roles and service identities can reach the affected operation, drop the component to the least privilege it actually needs, and review file and directory permissions created by earlier installs — a default left in place is what makes this reachable.

Is CVE-2021-39167 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-39167 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-2021-39167?

CVE-2021-39167 has an EPSS (Exploit Prediction Scoring System) score of 1.6%, placing it in the 75th 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-2021-39167?

CVE-2021-39167 is classified as Improper Privilege Management (CWE-269). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-39167 published, and has it been updated?

CVE-2021-39167 was published on August 27, 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-2021-39167 — @openzeppelin/contracts

CRITICALFix: OpenZeppelin/openzeppelin-contracts@cec4f2e

CVE-2021-39167 is a critical-severity (CVSS 9.8) Improper Privilege Management vulnerability in @openzeppelin/contracts. A fix is available for @openzeppelin/contracts — see the affected versions and patch details below.

TimelockController vulnerability in OpenZeppelin Contracts

Also known asGHSA-fg47-3c2x-m2wr

Published

Aug 27, 2021

Updated

Jul 22, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Oct 8, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

1.6%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs75th percentile — riskier than 75% of all scored CVEsHighest risk

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

How urgent is this, really

CVE-2021-39167 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,386 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

999Kdownloads / week

Description

Impact

A vulnerability in TimelockController allowed an actor with the executor role to take immediate control of the timelock, by resetting the delay to 0 and escalating privileges, thus gaining unrestricted access to assets held in the contract. Instances with the executor role set to "open" allow anyone to use the executor role, thus leaving the timelock at risk of being taken over by an attacker.

Patches

A fix is included in the following releases of @openzeppelin/contracts and @openzeppelin/contracts-upgradeable:

4.3.1
3.4.2
3.4.2-solc-0.7

Deployed instances of TimelockController should be replaced with a fixed version by migrating all assets, ownership, and roles.

Workarounds

Revoke the executor role from accounts not strictly under the team's control. We recommend revoking all executors that are not also proposers. When applying this mitigation, ensure there is at least one proposer and executor remaining.

References

Post-mortem.

Credits

The issue was identified by an anonymous white hat hacker through Immunefi.

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`	≥ 4.0.0&&< 4.3.1	4.3.1`npm install @openzeppelin/contracts@4.3.1`
📦npm	`@openzeppelin/contracts`	≥ 3.3.0&&< 3.4.2	3.4.2`npm install @openzeppelin/contracts@3.4.2`

Affected Products

1 product · 2 configurations

Application

contractsopenzeppelin

≥ 4.0.0 && < 4.3.1

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 4.3.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-39167 is resolved across your whole dependency graph.
Workarounds
Close the privilege gap rather than the entry point: audit which accounts, roles and service identities can reach the affected operation, drop the component to the least privilege it actually needs, and review file and directory permissions created by earlier installs — a default left in place is what makes this reachable.

Frequently Asked Questions

### Impact A vulnerability in `TimelockController` allowed an actor with the executor role to take immediate control of the timelock, by resetting the delay to 0 and escalating privileges, thus gaining unrestricted access to assets held in the contract. Instances with the executor role set to "open" allow anyone to use the executor role, thus leaving the timelock at risk of being taken over by an attacker. ### Patches A fix is included in the following releases of `@openzeppelin/contracts` and `@openzeppelin/contracts-upgradeable`: - 4.3.1 - 3.4.2 - 3.4.2-solc-0.7 Deployed instances of `Ti