CVE-2021-21604

Jenkins provides XML REST APIs to configure views, jobs, and other items. When deserialization fails because of invalid data, Jenkins 2.274 and earlier, LTS 2.263.1 and earlier stores invalid object references created through these endpoints in the Old Data Monitor. If an administrator discards the old data, some erroneous data submitted to these endpoints may be persisted.

This allows attackers with View/Create, Job/Create, Agent/Create, or their respective */Configure permissions to inject crafted content into Old Data Monitor that results in the instantiation of potentially unsafe objects when discarded by an administrator.\n\nJenkins 2.275, LTS 2.263.2 does not record submissions from users in Old Data Monitor anymore.

In case of problems, the Java system properties hudson.util.RobustReflectionConverter.recordFailuresForAdmins and hudson.util.RobustReflectionConverter.recordFailuresForAllAuthentications can be set to true to record configuration data submissions from administrators or all users, partially or completely disabling this fix.

Untrusted serialized data is processed by a deserializer that can instantiate arbitrary objects or execute code as a side effect. Typical impact: arbitrary code execution or logic abuse.

CVE-2021-21604 has a CVSS score of 8.0 (High). The vector is network-reachable, low privileges required, and user interaction required. 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-2021-21604? CVE-2021-21604 is a high-severity insecure deserialization vulnerability in org.jenkins-ci.main:jenkins-core (maven), affecting versions <= 2.263.1. It is fixed in 2.263.2, 2.275. Untrusted serialized data is processed by a deserializer that can instantiate arbitrary objects or execute code as a side effect.
2. How severe is CVE-2021-21604? CVE-2021-21604 has a CVSS score of 8.0 (High). 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-2021-21604? org.jenkins-ci.main:jenkins-core (maven) versions <= 2.263.1 is affected.
4. Is there a fix for CVE-2021-21604? Yes. CVE-2021-21604 is fixed in 2.263.2, 2.275. Upgrade to this version or later.
5. Is CVE-2021-21604 exploitable, and should I be worried? Whether CVE-2021-21604 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-2021-21604 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-2021-21604?
   • 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

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