CVE-2021-21684: Git Cross-Site Scripting Vulnerability

MODERATE
Advisory Identifier: GHSA-gghc-g8cj-4vfv
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CVSS 6.1
CWE-116 CWE-79
Published
Advisory Summary

CVE-2021-21684 is a MODERATE (CVSS 6.1) cross-site scripting vulnerability (CWE-116: Improper Encoding or Escaping of Output) affecting Git libraries in the Maven ecosystem. The issue involves stored xss vulnerability in jenkins git plugin. Remediation is available by upgrading affected packages to version 4.8.3.

CVE-2021-21684 at a Glance

CVE Identifier CVE-2021-21684
GHSA Identifier GHSA-gghc-g8cj-4vfv
Severity MODERATE
CVSS v3.1 Base Score 6.1
CWE Classification CWE-116: Improper Encoding or Escaping of Output
Affected Product Git
Package Ecosystem Maven
Published Date
Last Updated

Security Impact

CVSS: 6.1

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:R/S:C/C:L/I:L/A:N).

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

How to Fix CVE-2021-21684

To remediate this vulnerability, upgrade all affected Git 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.plugins:git fixed: 4.8.3 
<dependency>
    <groupId>org.jenkins-ci.plugins</groupId>
    <artifactId>git</artifactId>
    <version>4.8.3</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.plugins

How to Check if You Are Affected

To determine whether your Java application is affected by CVE-2021-21684, inspect your build dependencies using the Maven Dependency Plugin:

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

Analyze the terminal output to locate any version of Git in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.8.3), your application is affected.

Note: The mvn dependency:tree -Dincludes=org.jenkins-ci.plugins 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-116: Improper Encoding or Escaping of Output, where the product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. as a result, the intended structure of the message is not preserved. In Git, 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

Jenkins Git Plugin 4.8.2 and earlier does not escape the Git SHA-1 checksum parameters provided to commit notifications when displaying them in a build cause. This results in a stored cross-site scripting (XSS) vulnerability exploitable by attackers able to submit crafted commit notifications to the `/git/notifyCommit` endpoint. Jenkins Git Plugin 4.8.3 rejects Git SHA-1 checksum parameters that do not match the expected format. Existing values are sanitized when displayed on the UI. This vulnerability is only exploitable in Jenkins 2.314 and earlier, LTS 2.303.1 and earlier. See the [LTS upgrade guide](https://www.jenkins.io/doc/upgrade-guide/2.303/#SECURITY-2452).

CVE-2021-21684 Affected Git Versions

1 component(s)
Fixed Versions:
4.8.3
Product / Package Ecosystem Affected Versions Fixed Version
org.jenkins-ci.plugins:git
maven/org.jenkins-ci.plugins/git
Maven
< 4.8.3
4.8.3

References

NVD — CVE-2021-21684 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-21684
Security Fix Commit FIX COMMIT
https://github.com/jenkinsci/git-plugin/commit/5474cc942bfba60927be629ff47fb41c38c66741
Git Source Repository REPOSITORY
https://github.com/jenkinsci/git-plugin
Git Security Information SECURITY
https://www.jenkins.io/security/advisory/2021-10-06/#SECURITY-2499
Git Security Information SECURITY
http://www.openwall.com/lists/oss-security/2021/10/06/1

Frequently Asked Questions

What is CVE-2021-21684?
CVE-2021-21684 is a security vulnerability in Git involving Stored XSS vulnerability in Jenkins Git Plugin under CWE-116: Improper Encoding or Escaping of Output.
Which Git versions are affected?
Affected versions include releases prior to 4.8.3 across affected packages: org.jenkins-ci.plugins:git.
What version fixes CVE-2021-21684?
Upgrading to 4.8.3 (or the latest patched release for your respective branch) resolves the vulnerability.
Is git affected?
Yes, org.jenkins-ci.plugins:git is affected in releases prior to 4.8.3. Upgrade your dependency to 4.8.3 or later.
What is the CVSS score of CVE-2021-21684?
CVE-2021-21684 has a CVSS v3.1 base score of 6.1 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.
What CWE is associated with CVE-2021-21684?
CVE-2021-21684 is classified under CWE-116: Improper Encoding or Escaping of Output (The product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. As a result, the intended structure of the message is not preserved.).
How can I check Maven dependencies for CVE-2021-21684?
Run the dependency tree command: 'mvn dependency:tree -Dincludes=org.jenkins-ci.plugins'. 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
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-gghc-g8cj-4vfv",
  "modified" : "2023-10-27T16:02:41Z",
  "published" : "2022-05-24T19:16:59Z",
  "aliases" : [ "CVE-2021-21684" ],
  "summary" : "Stored XSS vulnerability in Jenkins Git Plugin",
  "details" : "Jenkins Git Plugin 4.8.2 and earlier does not escape the Git SHA-1 checksum parameters provided to commit notifications when displaying them in a build cause.\n\nThis results in a stored cross-site scripting (XSS) vulnerability exploitable by attackers able to submit crafted commit notifications to the `/git/notifyCommit` endpoint.\n\nJenkins Git Plugin 4.8.3 rejects Git SHA-1 checksum parameters that do not match the expected format. Existing values are sanitized when displayed on the UI.\n\nThis vulnerability is only exploitable in Jenkins 2.314 and earlier, LTS 2.303.1 and earlier. See the [LTS upgrade guide](https://www.jenkins.io/doc/upgrade-guide/2.303/#SECURITY-2452).",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.jenkins-ci.plugins:git"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.8.3"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.8.2"
    }
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-21684"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/jenkinsci/git-plugin/commit/5474cc942bfba60927be629ff47fb41c38c66741"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/jenkinsci/git-plugin"
  }, {
    "type" : "WEB",
    "url" : "https://www.jenkins.io/security/advisory/2021-10-06/#SECURITY-2499"
  }, {
    "type" : "WEB",
    "url" : "http://www.openwall.com/lists/oss-security/2021/10/06/1"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-116", "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2022-12-15T17:36:30Z",
    "nvd_published_at" : "2021-10-06T23:15:00Z"
  }
}