CVE-2021-21619 in Claim Plugin
Summary
by MITRE • 02/24/2021
Jenkins Claim Plugin 2.18.1 and earlier does not escape the user display name, resulting in a stored cross-site scripting (XSS) vulnerability exploitable by attackers who are able to control the display names of Jenkins users, either via the security realm, or directly inside Jenkins.
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Analysis
by VulDB Data Team • 02/24/2021
The Jenkins Claim Plugin version 2.18.1 and earlier contains a critical stored cross-site scripting vulnerability that arises from insufficient output escaping of user display names. This flaw exists within the plugin's handling of user-generated content where the system fails to properly sanitize or escape special characters in display names before rendering them in web interfaces. The vulnerability stems from a fundamental weakness in input validation and output encoding practices, allowing malicious actors to inject arbitrary JavaScript code into the application's user interface.
This stored XSS vulnerability operates through a predictable attack vector where an attacker with the ability to control user display names can manipulate the system to execute malicious scripts in the context of other users' browsers. The attack can be facilitated either through compromising the security realm configuration that allows for display name manipulation or by directly modifying user records within Jenkins itself. The plugin's failure to properly escape HTML and JavaScript characters during display name rendering creates persistent XSS payloads that remain active until manually removed from the system.
The operational impact of this vulnerability extends beyond simple data theft or session hijacking, as it enables attackers to perform a wide range of malicious activities including but not limited to credential harvesting, privilege escalation, and data exfiltration. When exploited, the vulnerability can allow attackers to impersonate legitimate users within Jenkins, access restricted build artifacts, modify job configurations, and potentially gain administrative privileges. The stored nature of this vulnerability means that once injected, malicious payloads persist indefinitely until manually removed, making it particularly dangerous for long-running Jenkins environments.
The technical flaw aligns with CWE-79 which specifically addresses cross-site scripting vulnerabilities resulting from insufficient output escaping or encoding of user-controllable data. This weakness represents a classic case of improper input validation and sanitization where the application assumes that user-provided display names are safe without proper sanitization before rendering them in HTML contexts. The vulnerability also maps to ATT&CK technique T1566.002 which covers phishing with malicious attachments, as attackers can craft malicious display names that when viewed by other users trigger XSS payloads.
Mitigation strategies should include immediate patching to Jenkins Claim Plugin version 2.19.0 or later where the XSS vulnerability has been addressed through proper output escaping mechanisms. Organizations should also implement additional security controls such as restricting user permissions for display name modifications, implementing content security policies to limit script execution, and conducting regular security audits of user management configurations. Network-level protections including web application firewalls can provide additional defense-in-depth measures while organizations should establish secure coding practices that mandate proper input validation and output encoding for all user-controllable data in web applications.