CVE-2021-21626: 
Java vulnerability analysis and mitigation

CVE-2021-21626 is a security vulnerability discovered in the Jenkins Warnings Plugin (warnings-ng) version 8.4.4 and earlier. The vulnerability was disclosed on March 18, 2021, and involves missing permission checks in methods implementing form validation. This security issue affects Jenkins installations using the Warnings Plugin up to and including version 8.4.4 (Jenkins Advisory).

The vulnerability stems from the plugin's failure to perform permission checks in methods implementing form validation. The severity is rated as Medium according to the CVSS scoring system. The technical issue allows attackers with Item/Read permission to bypass additional required permissions (Item/Workspace or Item/Configure) when validating file patterns against workspace contents (Jenkins Advisory).

The vulnerability enables attackers with basic Item/Read permission to check whether attacker-specified file patterns match workspace contents, even without having the normally required Item/Workspace or Item/Configure permissions. Through a sequence of requests, attackers can effectively enumerate and list workspace contents, potentially exposing sensitive information (Jenkins Advisory, OSS Security).

The vulnerability requires an attacker to have Item/Read permission on the Jenkins instance but does not require the normally mandatory Item/Workspace or Item/Configure permissions. The exploitation can be achieved through a sequence of specially crafted requests to the form validation endpoints (Jenkins Advisory).

The vulnerability was fixed in Warnings Plugin version 8.5.0, which implements proper permission checks by requiring Item/Configure permission to validate patterns with workspace contents. Users are advised to upgrade to this version or later to address the security issue (Jenkins Advisory).