CVE-2021-21609

Jenkins includes a static list of URLs that are always accessible even without Overall/Read permission, such as the login form. These URLs are excluded from an otherwise universal permission check.

Jenkins 2.274 and earlier, LTS 2.263.1 and earlier does not correctly compare requested URLs with that list.

This allows attackers without Overall/Read permission to access plugin-provided URLs with any of the following prefixes if no other permissions are required:

• accessDenied
• error
• instance-identity
• login
• logout
• oops
• securityRealm
• signup
• tcpSlaveAgentListener

For example, a plugin contributing the path loginFoo/ would have URLs in that space accessible without the default Overall/Read permission check.

The Jenkins security team is not aware of any affected plugins as of the publication of this advisory.

The comparison of requested URLs with the list of always accessible URLs has been fixed to only allow access to the specific listed URLs in Jenkins 2.275, LTS 2.263.2.

In case this change causes problems, additional paths can be made accessible without Overall/Read permissions: The Java system property jenkins.model.Jenkins.additionalReadablePaths is a comma-separated list of additional path prefixes to allow access to.

The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions. Typical impact: unauthorized data access or execution of privileged operations.

CVE-2021-21609 has a CVSS score of 5.3 (Medium). 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 (2.263.2, 2.275); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2021-21609? CVE-2021-21609 is a medium-severity incorrect authorization vulnerability in org.jenkins-ci.main:jenkins-core (maven), affecting versions <= 2.263.1. It is fixed in 2.263.2, 2.275. The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions.
2. How severe is CVE-2021-21609? CVE-2021-21609 has a CVSS score of 5.3 (Medium). 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.
3. Which versions of org.jenkins-ci.main:jenkins-core are affected by CVE-2021-21609? org.jenkins-ci.main:jenkins-core (maven) versions <= 2.263.1 is affected.
4. Is there a fix for CVE-2021-21609? Yes. CVE-2021-21609 is fixed in 2.263.2, 2.275. Upgrade to this version or later.
5. Is CVE-2021-21609 exploitable, and should I be worried? Whether CVE-2021-21609 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
6. What actually determines whether CVE-2021-21609 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.
7. How do I fix CVE-2021-21609?
   • Upgrade org.jenkins-ci.main:jenkins-core to 2.263.2 or later
   • Upgrade org.jenkins-ci.main:jenkins-core to 2.275 or later

Other vulnerabilities in org.jenkins-ci.main:jenkins-core