CVE-2023-27898: Jenkins Stored XSS Vulnerability

CVE-2023-27898 Overview

CVE-2023-27898 is a stored cross-site scripting (XSS) vulnerability affecting Jenkins, the widely-used open-source automation server. The vulnerability exists because Jenkins fails to properly escape the Jenkins version string that a plugin depends on when rendering error messages about plugin incompatibility with the current Jenkins version. This flaw allows attackers who can provide plugins to configured update sites to inject malicious scripts that execute when Jenkins administrators view the incompatibility error message.

Critical Impact

This stored XSS vulnerability can enable attackers to execute arbitrary JavaScript in the context of authenticated Jenkins administrators, potentially leading to credential theft, session hijacking, or complete compromise of the Jenkins environment and connected CI/CD pipelines.

Affected Products

• Jenkins 2.270 through 2.393 (weekly releases)
• Jenkins LTS 2.277.1 through 2.375.3
• Any Jenkins instance configured to use update sites controlled or influenced by attackers

Discovery Timeline

• 2023-03-08 - Jenkins publishes security advisory SECURITY-3037
• 2023-03-10 - CVE-2023-27898 published to NVD
• 2025-02-28 - Last updated in NVD database

Technical Details for CVE-2023-27898

Vulnerability Analysis

This vulnerability is classified as CWE-79 (Improper Neutralization of Input During Web Page Generation - Cross-Site Scripting). The flaw resides in Jenkins' plugin management functionality, specifically in how the application renders error messages when a plugin declares a dependency on a specific Jenkins version that is incompatible with the currently running instance.

When Jenkins displays these incompatibility error messages to administrators, it includes the version string specified by the plugin without proper HTML encoding or sanitization. This creates an injection point where malicious content embedded in the version string is rendered as executable HTML/JavaScript rather than being safely displayed as text.

The attack requires that an adversary has the ability to provide plugins to update sites that the target Jenkins instance is configured to use. This could occur through compromise of official or third-party update sites, man-in-the-middle attacks on update channels, or through social engineering administrators to add malicious update site URLs.

Root Cause

The root cause is insufficient output encoding in the Jenkins UI rendering code. When constructing the error message for plugin version incompatibility, the application directly interpolates the version string from the plugin manifest into the HTML output without applying proper escaping functions. This violates secure coding principles that require all dynamic content to be contextually encoded before being rendered in web pages.

Attack Vector

The attack follows a supply-chain-style exploitation pattern:

1. Plugin Preparation: The attacker creates or modifies a malicious plugin that declares a dependency on a specially crafted Jenkins "version" string containing XSS payloads
2. Distribution: The malicious plugin is distributed through an update site that the target Jenkins instance trusts or can be tricked into trusting
3. Trigger: When a Jenkins administrator browses available plugins or updates, Jenkins attempts to validate the plugin's dependencies
4. Execution: Upon detecting the version incompatibility, Jenkins renders an error message containing the unescaped malicious version string, causing the XSS payload to execute in the administrator's browser

The stored nature of this XSS means the payload persists and can execute multiple times whenever the affected error message is displayed, increasing the attack's impact and reliability.

Detection Methods for CVE-2023-27898

Indicators of Compromise

• Unusual JavaScript execution or browser behavior when accessing Jenkins plugin management pages
• Unexpected outbound network connections from administrator browsers while viewing Jenkins
• Modified Jenkins configurations, credentials, or user accounts that cannot be attributed to legitimate administrator actions
• Plugin entries in update site metadata containing HTML tags, script elements, or JavaScript event handlers in version fields

Detection Strategies

• Review Jenkins access logs for anomalous patterns of plugin management page access
• Implement Content Security Policy (CSP) headers to detect and block inline script execution attempts
• Monitor update site configurations for unauthorized changes or additions of untrusted sources
• Deploy web application firewalls capable of detecting XSS payload patterns in HTTP responses

Monitoring Recommendations

• Enable detailed audit logging for all Jenkins administrative actions and configuration changes
• Configure browser-based XSS protection mechanisms and monitor for triggered alerts
• Establish baseline behavior for plugin management activities and alert on deviations
• Monitor for changes to Jenkins security realm configurations or credential stores

How to Mitigate CVE-2023-27898

Immediate Actions Required

• Upgrade Jenkins weekly releases to version 2.394 or later immediately
• Upgrade Jenkins LTS installations to version 2.375.4 or later
• Audit all configured update sites and remove any untrusted or unnecessary sources
• Review recent administrative activities for signs of compromise following any suspected exposure

Patch Information

Jenkins has released patched versions that properly escape version strings when rendering plugin incompatibility error messages. The fix is included in:

• Jenkins weekly release 2.394 and later
• Jenkins LTS 2.375.4 and later

Administrators should apply these updates as soon as possible. The official Jenkins Security Advisory 2023-03-08 provides complete details about this vulnerability and the remediation.

Workarounds

• Restrict update site configurations to only the official Jenkins update center until patching is complete
• Limit network access from Jenkins instances to prevent connections to potentially malicious update sites
• Implement strict Content Security Policy headers on the Jenkins web interface to mitigate XSS impact
• Consider temporary restrictions on access to plugin management functionality for non-essential administrators

# Verify current Jenkins version
java -jar jenkins.war --version

# Check configured update sites (from Jenkins script console)
# Navigate to: Manage Jenkins > Script Console
# jenkins.model.Jenkins.instance.updateCenter.sites.each { println it.url }

# After upgrading, verify the new version
# The patched versions are: Weekly >= 2.394, LTS >= 2.375.4