CVE-2021-21697: Jenkins core Agent-to-controller Access Control Allows Reading/writing Vulnerability

CRITICAL
Advisory Identifier: GHSA-cv2w-q8c3-xjv7
CVSS 9.1
CWE-184
Published
Advisory Summary

CVE-2021-21697 is a CRITICAL (CVSS 9.1) agent-to-controller access control allows reading/writing vulnerability (CWE-184: Incomplete List of Disallowed Inputs) affecting Jenkins core libraries in the Maven ecosystem. The issue involves agent-to-controller access control allows reading/writing most content of build directories in jenkins. Remediation is available by upgrading affected packages to version 2.303.3, 2.319.

CVE-2021-21697 at a Glance

CVE Identifier CVE-2021-21697
GHSA Identifier GHSA-cv2w-q8c3-xjv7
Severity CRITICAL
CVSS v3.1 Base Score 9.1
CWE Classification CWE-184: Incomplete List of Disallowed Inputs
Affected Product Jenkins core
Package Ecosystem Maven
Published Date
Last Updated

Security Impact

CVSS: 9.1

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity High (I:H)
Availability None (A:N)

How to Fix CVE-2021-21697

To remediate this vulnerability, upgrade all affected Jenkins core dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

org.jenkins-ci.main:jenkins-core fixed: 2.303.3
<dependency>
    <groupId>org.jenkins-ci.main</groupId>
    <artifactId>jenkins-core</artifactId>
    <version>2.303.3</version>
</dependency>
org.jenkins-ci.main:jenkins-core fixed: 2.319
<dependency>
    <groupId>org.jenkins-ci.main</groupId>
    <artifactId>jenkins-core</artifactId>
    <version>2.319</version>
</dependency>
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release:

mvn dependency:tree -Dincludes=org.jenkins-ci.main

How to Check if You Are Affected

To determine whether your Java application is affected by CVE-2021-21697, inspect your build dependencies using the Maven Dependency Plugin:

mvn dependency:tree -Dincludes=org.jenkins-ci.main

Analyze the terminal output to locate any version of Jenkins core in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.303.3), your application is affected.

Note: The mvn dependency:tree -Dincludes=org.jenkins-ci.main command inspects the resolved dependency graph declared in your project's POM files; it does not perform automated security scanning or inspect runtime dynamic classpaths. Always verify runtime container classpaths and shaded JARs.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-184: Incomplete List of Disallowed Inputs, where the product implements a protection mechanism that relies on a list of inputs (or properties of inputs) that are not allowed by policy or otherwise require other action to neutralize before additional processing takes place, but the list is incomplete. In Jenkins core, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

Agents are allowed some limited access to files on the Jenkins controller file system. The directories agents are allowed to access in Jenkins 2.318 and earlier, LTS 2.303.2 and earlier include the directories storing build-related information, intended to allow agents to store build-related metadata during build execution. As a consequence, this allows any agent to read and write the contents of any build directory stored in Jenkins with very few restrictions (`build.xml` and some Pipeline-related metadata). Jenkins 2.319, LTS 2.303.3 prevents agents from accessing contents of build directories unless it’s for builds currently running on the agent attempting to access the directory. Update [Pipeline: Nodes and Processes](https://plugins.jenkins.io/workflow-durable-task-step/) to version 2.40 or newer for Jenkins to associate Pipeline `node` blocks with the agent they’re running on for this fix. If you are unable to immediately upgrade to Jenkins 2.319, LTS 2.303.3, you can install the [Remoting Security Workaround Plugin](https://www.jenkins.io/redirect/remoting-security-workaround/). 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.

CVE-2021-21697 Affected Jenkins core Versions

2 component(s)
Fixed Versions:
2.303.32.319
Product / Package Ecosystem Affected Versions Fixed Version
org.jenkins-ci.main:jenkins-core
Maven
< 2.303.3
2.303.3
org.jenkins-ci.main:jenkins-core
Maven
≥ 2.304
< 2.319
2.319

References

Frequently Asked Questions

What is CVE-2021-21697?
CVE-2021-21697 is a security vulnerability in Jenkins core involving Agent-to-controller access control allows reading/writing most content of build directories in Jenkins under CWE-184: Incomplete List of Disallowed Inputs.
Which Jenkins core versions are affected?
Affected versions include releases prior to 2.303.3, 2.319 across affected packages: org.jenkins-ci.main:jenkins-core.
What version fixes CVE-2021-21697?
Upgrading to 2.303.3, 2.319 (or the latest patched release for your respective branch) resolves the vulnerability.
Is jenkins-core affected?
Yes, org.jenkins-ci.main:jenkins-core is affected in releases prior to 2.303.3, 2.319. Upgrade your dependency to 2.303.3, 2.319 or later.
What is the CVSS score of CVE-2021-21697?
CVE-2021-21697 has a CVSS v3.1 base score of 9.1 (CRITICAL) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N.
What CWE is associated with CVE-2021-21697?
CVE-2021-21697 is classified under CWE-184: Incomplete List of Disallowed Inputs (The product implements a protection mechanism that relies on a list of inputs (or properties of inputs) that are not allowed by policy or otherwise require other action to neutralize before additional processing takes place, but the list is incomplete.).
How can I check Maven dependencies for CVE-2021-21697?
Run the dependency tree command: 'mvn dependency:tree -Dincludes=org.jenkins-ci.main'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-cv2w-q8c3-xjv7",
  "modified" : "2023-12-18T11:30:58Z",
  "published" : "2022-05-24T19:19:43Z",
  "aliases" : [ "CVE-2021-21697" ],
  "summary" : "Agent-to-controller access control allows reading/writing most content of build directories in Jenkins",
  "details" : "Agents are allowed some limited access to files on the Jenkins controller file system. The directories agents are allowed to access in Jenkins 2.318 and earlier, LTS 2.303.2 and earlier include the directories storing build-related information, intended to allow agents to store build-related metadata during build execution. As a consequence, this allows any agent to read and write the contents of any build directory stored in Jenkins with very few restrictions (`build.xml` and some Pipeline-related metadata).\n\nJenkins 2.319, LTS 2.303.3 prevents agents from accessing contents of build directories unless it’s for builds currently running on the agent attempting to access the directory.\n\nUpdate [Pipeline: Nodes and Processes](https://plugins.jenkins.io/workflow-durable-task-step/) to version 2.40 or newer for Jenkins to associate Pipeline `node` blocks with the agent they’re running on for this fix.\n\nIf you are unable to immediately upgrade to Jenkins 2.319, LTS 2.303.3, you can install the [Remoting Security Workaround Plugin](https://www.jenkins.io/redirect/remoting-security-workaround/). 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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.jenkins-ci.main:jenkins-core"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.303.3"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 2.303.2"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.jenkins-ci.main:jenkins-core"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.304"
      }, {
        "fixed" : "2.319"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 2.318"
    }
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-21697"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/jenkinsci/jenkins/commit/cf388d2a04e6016d23eb93fa3cc804f2554b98f0"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/jenkinsci/jenkins/commit/eae33841b587da787f37d5b6c8451d483edc04d9"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/jenkinsci/jenkins"
  }, {
    "type" : "WEB",
    "url" : "https://www.jenkins.io/security/advisory/2021-11-04/#SECURITY-2428"
  }, {
    "type" : "WEB",
    "url" : "http://www.openwall.com/lists/oss-security/2021/11/04/3"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-184" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2022-06-23T06:46:48Z",
    "nvd_published_at" : "2021-11-04T17:15:00Z"
  }
}