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JenkinsApplication

CVE-2021-21686

HIGH · 8.1 CVSS v3.1 Published 2021-11-04
Fix available
A fix is available. Upgrade to 2.303.3 / 2.319 or later.
See remediation →
88/100
Remediation priority · High
Remotely reachable No privileges

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 · unedited
File path filters in the agent-to-controller security subsystem of Jenkins 2.318 and earlier, LTS 2.303.2 and earlier do not canonicalize paths, allowing operations to follow symbolic links to outside allowed directories.

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 confidence

Jenkins agent-to-controller security subsystem fails to canonicalize file paths before validation, enabling symbolic link traversal to access files outside permitted directories. An attacker with agent access could bypass path restrictions and read/write arbitrary files on the Jenkins controller.

MitigationUpgrade Jenkins to version 2.319/LTS 2.303.3 or later which implements proper path canonicalization in the security filter.

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
Affected:< 2.303.3< 2.319

CVSS 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
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/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 checks

Work through these to decide whether this CVE applies to you.

  1. Check the installed Jenkins version
    Run 'java -jar jenkins-cli.jar version' or access /api/json?tree=version from the Jenkins UI, or check the jenkins.war file properties
    Affected if The version is lower than 2.303.3 or between 2.303.3 and 2.319 (exclusive)
  2. Determine if agent connections are enabled
    Navigate to Manage Jenkins > Manage Nodes > Manage Agents, or inspect the Jenkins configuration file (jenkins.model.Jenkins.locationConfigUrl) for agent-related settings
    Affected if Agents are enabled and reachable on the Jenkins controller
  3. Verify the security filter configuration
    Review the security realm and authorization strategy settings under Manage Jenkins > Global Security, specifically looking for agent-to-controller access control settings
    Affected if Agent-to-controller file access control is configured but path canonicalization is not enforced
  4. Check for existing symbolic link artifacts
    Inspect agent workspace directories under $JENKINS_HOME/agents/ for any unexpected symbolic links pointing outside permitted paths
    Affected if Symbolic links exist that escape the designated agent workspace directories

You are affected if your Jenkins version is below 2.303.3 or below 2.319 AND agents are enabled, since the vulnerability requires agent access to exploit the path canonicalization bypass.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 · scoped
Upgrade available Upgrade to 2.303.3 / 2.319 or later
Fixed in 2.303.32.319
Interim mitigation

Upgrade Jenkins to version 2.319/LTS 2.303.3 or later which implements proper path canonicalization in the security filter.

Recommended fix High confidence

Jenkins 2.319 (weekly) or Jenkins 2.303.3 LTS

  1. Back up your Jenkins home directory and any critical configurations
  2. Download Jenkins 2.319 (weekly) or Jenkins 2.303.3 LTS from the official Jenkins website (jenkins.io)
  3. Stop the Jenkins service
  4. Replace the Jenkins WAR file or update via your package manager (depending on your installation method)
  5. Start the Jenkins service
  6. Verify the upgrade was successful by checking the Jenkins version in the UI or via CLI
  7. Review plugin compatibility after upgrade, as needed
Caveat Standard LTS upgrades are typically backward compatible; verify plugin compatibility especially if running older plugins

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Jenkins Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA3.0 h
15.0 hours of engineering $2,560
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,096.

Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-21686 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • 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
  • No spam, self-promotion, credentials, or personal data