CVE-2021-21684: 
Java vulnerability analysis and mitigation

CVE-2021-21684 is a stored cross-site scripting (XSS) vulnerability discovered in the Jenkins Git Plugin versions 4.8.2 and earlier. The vulnerability stems from the plugin's failure to properly escape Git SHA-1 checksum parameters that are provided to commit notifications when displaying them in a build cause (Jenkins Advisory, CVE Mitre).

The vulnerability is classified with a High severity CVSS rating. The issue specifically occurs in the handling of Git SHA-1 checksum parameters within commit notifications, where the lack of proper escaping creates a security weakness. The vulnerability is only exploitable in Jenkins 2.314 and earlier, as well as LTS 2.303.1 and earlier versions (Jenkins Advisory).

The vulnerability allows attackers to execute a stored cross-site scripting (XSS) attack by submitting crafted commit notifications to the /git/notifyCommit endpoint. This could potentially lead to unauthorized access and manipulation of Jenkins system data (Jenkins Advisory).

The vulnerability has been fixed in Git Plugin version 4.8.3, which implements two security measures: it rejects Git SHA-1 checksum parameters that don't match the expected format and sanitizes existing values when displayed on the UI. Users are strongly advised to update to Jenkins weekly version 2.315, Jenkins LTS version 2.303.2, and Git Plugin version 4.8.3 (Jenkins Advisory).