Summary
TimelockController vulnerability in OpenZeppelin Contracts
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
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].
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.
The application assigns, modifies, tracks, or checks privileges incorrectly, allowing a user to gain elevated access. Typical impact: privilege escalation beyond the intended level.
CVE-2021-39168 has a CVSS score of 10.0 (Critical). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.3.1, 3.4.2); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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See it in your environmentNew to Kodem? Get a demo →Remediation advice
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.
Frequently Asked Questions
- What is CVE-2021-39168? CVE-2021-39168 is a critical-severity improper privilege management vulnerability in @openzeppelin/contracts-upgradeable (npm), affecting versions >= 4.0.0, < 4.3.1. It is fixed in 4.3.1, 3.4.2. The application assigns, modifies, tracks, or checks privileges incorrectly, allowing a user to gain elevated access.
- How severe is CVE-2021-39168? CVE-2021-39168 has a CVSS score of 10.0 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of @openzeppelin/contracts-upgradeable are affected by CVE-2021-39168? @openzeppelin/contracts-upgradeable (npm) versions >= 4.0.0, < 4.3.1 is affected.
- Is there a fix for CVE-2021-39168? Yes. CVE-2021-39168 is fixed in 4.3.1, 3.4.2. Upgrade to this version or later.
- Is CVE-2021-39168 exploitable, and should I be worried? Whether CVE-2021-39168 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2021-39168 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2021-39168?
- Upgrade
@openzeppelin/contracts-upgradeableto 4.3.1 or later - Upgrade
@openzeppelin/contracts-upgradeableto 3.4.2 or later
- Upgrade