JenkinsApplication
CVE-2021-21687
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedJenkins 2.318 and earlier, LTS 2.303.2 and earlier does not check agent-to-controller access to create symbolic links when unarchiving a symbolic link in FilePath#untar.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceJenkins versions 2.318 and earlier, LTS 2.303.2 and earlier fail to validate agent-to-controller access permissions when unarchiving symbolic links via the FilePath#untar method. This allows compromised or malicious agents to create arbitrary symbolic links on the Jenkins controller file system, potentially enabling path traversal, privilege escalation, or remote code execution.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
JenkinsApplication
< 2.303.3< 2.319CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify the installed Jenkins versionNavigate to Manage Jenkins > About Jenkins, or check the version displayed on the login page, or run: java -jar jenkins.war --versionAffected if The version shown is earlier than 2.303.3 for LTS or earlier than 2.319 for weekly releases
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Confirm if Jenkins agents are configuredNavigate to Manage Jenkins > Manage Nodes. Check if any permanent or temporary agents are defined and connected.Affected if Agents are defined and connected, creating the attack surface for this vulnerability
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Verify if the FilePath#untar functionality is accessibleReview Jenkins job configurations or scripts that use the 'untar' operation, particularly those running on agents that could supply malicious archive content.Affected if Any jobs or pipelines use the untar or similar archive extraction operations on agent nodes
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Inspect for unexpected symbolic links on the controllerRun 'find / -type l -ls' (Linux) or 'Get-ChildItem -Recurse -Link | Format-Table FullName, Target' (Windows) to list all symbolic links on the Jenkins controller filesystem.Affected if Symbolic links exist in directories outside of expected locations such as agent workspaces or known archive extraction directories
A user is affected if their Jenkins version is earlier than 2.303.3 (LTS) or 2.319 (weekly) AND they have agents configured with access to the untar functionality.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped2.303.32.319
Upgrade Jenkins to version 2.319+ (LTS 2.303.3+) which includes the proper permission check for agent-to-controller access during symbolic link creation in unarchiving operations.
Jenkins 2.319 (weekly) or Jenkins LTS 2.303.3
- 1. Backup your Jenkins home directory and any critical data
- 2. Review the Jenkins 2.319 and LTS 2.303.3 release notes for any relevant changes
- 3. Stop the Jenkins service
- 4. Upgrade Jenkins to version 2.319 or later (weekly) / LTS 2.303.3 or later
- 5. Start the Jenkins service
- 6. Verify the controller can no longer be affected by unauthorized agent symlink creation
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Jenkins
Scoped from the published advisory
- Consultation3.0 h
- Implementation4.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,648.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-21687 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-21687 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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