CVE-2023-27905: Jenkins Update-center2 XSS Vulnerability

CVE-2023-27905 Overview

CVE-2023-27905 is a stored cross-site scripting (XSS) vulnerability affecting Jenkins update-center2 versions 3.13 and 3.14. The vulnerability occurs because the update-center2 component renders the required Jenkins core version on plugin download index pages without proper sanitization. This allows attackers who can provide a plugin for hosting to inject malicious scripts that execute in the context of other users' browsers when they visit the affected pages.

Critical Impact

Attackers can exploit this stored XSS vulnerability to execute arbitrary JavaScript code in victims' browsers, potentially stealing session cookies, performing actions on behalf of authenticated Jenkins administrators, or compromising the entire CI/CD pipeline infrastructure.

Affected Products

• Jenkins update-center2 3.13
• Jenkins update-center2 3.14

Discovery Timeline

• 2023-03-08 - Jenkins releases security advisory SECURITY-3063
• 2023-03-10 - CVE CVE-2023-27905 published to NVD
• 2025-02-28 - Last updated in NVD database

Technical Details for CVE-2023-27905

Vulnerability Analysis

This stored XSS vulnerability resides in the Jenkins update-center2 component, which is responsible for generating plugin download index pages. The root issue stems from insufficient input validation and output encoding when handling the required Jenkins core version metadata associated with plugins.

When a malicious actor submits a plugin to the Jenkins update center with a crafted Jenkins core version requirement, the unsanitized value is stored and subsequently rendered directly into HTML pages. This creates a persistent XSS condition where any user visiting the affected plugin download page will have the malicious script executed in their browser context.

The attack is particularly dangerous in Jenkins environments because successful exploitation could allow attackers to steal administrator credentials, inject backdoors into build pipelines, or pivot to compromise connected systems. Given that Jenkins is commonly used in enterprise CI/CD workflows, the blast radius of such an attack could extend to production deployment systems.

Root Cause

The vulnerability originates from missing input sanitization in the update-center2 component when processing and rendering plugin metadata. Specifically, the required Jenkins core version field is rendered directly into HTML output without proper encoding or escaping, allowing HTML and JavaScript injection. This represents a classic CWE-79 (Improper Neutralization of Input During Web Page Generation) weakness where untrusted data is included in web page output without adequate validation.

Attack Vector

The attack requires an adversary to have the ability to provide a plugin for hosting on a Jenkins update center. The attacker crafts a malicious plugin package where the required Jenkins core version metadata contains XSS payloads such as script tags or event handlers. When this plugin is indexed by update-center2 and users browse the plugin download pages, the malicious payload executes in their browsers.

The attack vector is network-based, requires user interaction (visiting the affected page), and can cross security boundaries to impact resources beyond the vulnerable component. Since the malicious content is stored server-side, any user who views the affected plugin page becomes a potential victim without requiring direct interaction with the attacker.

Detection Methods for CVE-2023-27905

Indicators of Compromise

• Unusual JavaScript content in plugin metadata fields, particularly in the required Jenkins core version
• Unexpected network requests originating from Jenkins update center pages to external domains
• Reports of browser security warnings or content security policy violations when accessing plugin index pages
• Suspicious plugin submissions containing HTML tags or script elements in metadata fields

Detection Strategies

• Review web server access logs for requests to plugin index pages followed by unusual external resource loading
• Implement Content Security Policy (CSP) headers to detect and block inline script execution attempts
• Monitor for anomalous authentication or session activity following visits to update center pages
• Audit plugin metadata submissions for HTML/JavaScript injection patterns

Monitoring Recommendations

• Enable comprehensive logging for the Jenkins update center infrastructure
• Deploy web application firewalls (WAF) with XSS detection rules to identify malicious payloads
• Implement browser-based security monitoring to detect client-side script injection attacks
• Set up alerts for unusual patterns in plugin metadata submissions

How to Mitigate CVE-2023-27905

Immediate Actions Required

• Upgrade Jenkins update-center2 to a patched version (versions after 3.14)
• Review recently submitted plugins for malicious metadata content
• Implement Content Security Policy headers as a defense-in-depth measure
• Audit access to plugin hosting capabilities and restrict to trusted entities

Patch Information

Jenkins has addressed this vulnerability in versions following update-center2 3.14. Organizations should consult the Jenkins Security Advisory 2023-03-08 for detailed patch information and upgrade instructions. The fix implements proper output encoding for the required Jenkins core version field when rendering plugin download index pages.

Workarounds

• Restrict plugin hosting capabilities to verified and trusted contributors only
• Implement strict Content Security Policy headers to mitigate XSS impact: Content-Security-Policy: script-src 'self'
• Deploy a web application firewall with XSS filtering rules in front of update center infrastructure
• Regularly audit plugin metadata for suspicious content before publication

# Example Content Security Policy configuration for nginx
# Add to server block to mitigate XSS attacks
add_header Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'; img-src 'self' data:; frame-ancestors 'self';" always;