Summary
The agent-to-controller security subsystem limits which files on the Jenkins controller can be accessed by agent processes.
Multiple vulnerabilities in the file path filtering implementation of Jenkins 2.318 and earlier, LTS 2.303.2 and earlier allow agent processes to read and write arbitrary files on the Jenkins controller file system, and obtain some information about Jenkins controller file systems.
SECURITY-2539 / CVE-2021-21693: When creating temporary files, permission to create files is only checked after they’ve been created.
We expect that most of these vulnerabilities have been present since SECURITY-144 was addressed in the 2014-10-30 security advisory.
Jenkins 2.319, LTS 2.303.3 addresses these security vulnerabilities.
SECURITY-2539 / CVE-2021-21693: When creating temporary files, permission to create files is checked before they are created based on an artificial path.
As some common operations are now newly subject to access control, it is expected that plugins sending commands from agents to the controller may start failing. Additionally, the newly introduced path canonicalization means that instances using a custom builds directory (Java system property jenkins.model.Jenkins.buildsDir) or partitioning JENKINS_HOME using symbolic links may fail access control checks. See the documentation for how to customize the configuration in case of problems.
If you are unable to immediately upgrade to Jenkins 2.319, LTS 2.303.3, you can install the Remoting Security Workaround Plugin. It will prevent all agent-to-controller file access using FilePath APIs. Because it is more restrictive than Jenkins 2.319, LTS 2.303.3, more plugins are incompatible with it. Make sure to read the plugin documentation before installing it.
Impact
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-2021-21693 has a CVSS score of 9.0 (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 (2.319, 2.303.3); 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.
Remediation advice
org.jenkins-ci.main:jenkins-core to 2.319 or later; org.jenkins-ci.main:jenkins-core to 2.303.3 or later
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2021-21693? CVE-2021-21693 is a critical-severity incorrect authorization vulnerability in org.jenkins-ci.main:jenkins-core (maven), affecting versions >= 2.304, <= 2.318. It is fixed in 2.319, 2.303.3. The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions.
- How severe is CVE-2021-21693? CVE-2021-21693 has a CVSS score of 9.0 (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 org.jenkins-ci.main:jenkins-core are affected by CVE-2021-21693? org.jenkins-ci.main:jenkins-core (maven) versions >= 2.304, <= 2.318 is affected.
- Is there a fix for CVE-2021-21693? Yes. CVE-2021-21693 is fixed in 2.319, 2.303.3. Upgrade to this version or later.
- Is CVE-2021-21693 exploitable, and should I be worried? Whether CVE-2021-21693 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-2021-21693 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-2021-21693?
- Upgrade
org.jenkins-ci.main:jenkins-coreto 2.319 or later - Upgrade
org.jenkins-ci.main:jenkins-coreto 2.303.3 or later
- Upgrade