CVE-2026-42524: Jenkins HTML Publisher Plugin XSS Flaw

CVE-2026-42524 Overview

CVE-2026-42524 is a stored Cross-Site Scripting (XSS) vulnerability affecting the Jenkins HTML Publisher Plugin version 427 and earlier. The vulnerability exists because the plugin fails to properly escape job name and URL values when writing them to the legacy wrapper file. This allows attackers with Item/Configure permission to inject malicious scripts that persist and execute in the browsers of other users who view the affected content.

Critical Impact

Attackers with Item/Configure permission can inject persistent malicious scripts that execute in the context of other Jenkins users, potentially leading to session hijacking, credential theft, or further compromise of the Jenkins environment.

Affected Products

• Jenkins HTML Publisher Plugin version 427 and earlier

Discovery Timeline

• 2026-04-29 - CVE CVE-2026-42524 published to NVD
• 2026-04-29 - Last updated in NVD database

Technical Details for CVE-2026-42524

Vulnerability Analysis

This vulnerability is classified as CWE-79 (Improper Neutralization of Input During Web Page Generation), commonly known as Cross-Site Scripting. The HTML Publisher Plugin provides functionality to publish HTML reports from Jenkins jobs, making them accessible through the Jenkins web interface. When generating the legacy wrapper file that displays these reports, the plugin directly incorporates the job name and URL values without applying proper output encoding or sanitization.

The stored nature of this XSS vulnerability means that the malicious payload persists within the Jenkins environment. Once an attacker with Item/Configure permission creates or modifies a job with a crafted name containing JavaScript code, that code will execute whenever any user views the affected HTML report wrapper. This persistence makes stored XSS particularly dangerous compared to reflected XSS variants.

Root Cause

The root cause lies in insufficient output encoding within the legacy wrapper file generation logic. When the HTML Publisher Plugin constructs the wrapper page, it interpolates the job name and URL directly into the HTML output without escaping special characters such as <, >, ", and '. This allows an attacker to break out of the expected HTML context and inject arbitrary JavaScript code.

Attack Vector

The attack requires the attacker to have Item/Configure permission within Jenkins, which allows them to create or modify Jenkins jobs. The attacker crafts a job name containing malicious JavaScript that, when rendered in the legacy wrapper file, executes in the browsers of other Jenkins users viewing the published HTML reports.

The attack vector is network-based and requires user interaction—specifically, a victim must navigate to the page containing the injected script. However, in a typical Jenkins environment where teams regularly review build reports, this condition is easily met. The vulnerability could be exploited to steal session cookies, perform actions on behalf of authenticated administrators, or pivot to further attacks against the Jenkins infrastructure.

Detection Methods for CVE-2026-42524

Indicators of Compromise

• Unusual or suspicious characters in Jenkins job names, particularly those containing <script> tags, event handlers (e.g., onerror, onload), or encoded JavaScript payloads
• Unexpected modifications to job configurations by users with Item/Configure permission
• Browser console errors or unexpected script execution when viewing HTML Publisher reports
• User reports of unexpected behavior or redirects when accessing Jenkins reports

Detection Strategies

• Review Jenkins audit logs for job configuration changes that include special HTML characters or JavaScript keywords in job names
• Implement Content Security Policy (CSP) headers to detect and block inline script execution
• Deploy web application firewalls (WAF) to monitor for XSS patterns in Jenkins traffic
• Use browser developer tools to inspect HTML Publisher wrapper pages for injected script content

Monitoring Recommendations

• Enable Jenkins security audit logging to track job configuration changes
• Monitor for anomalous user session activity that could indicate session hijacking
• Implement alerting on job names containing potentially malicious patterns
• Review HTML Publisher plugin usage and identify affected job configurations

How to Mitigate CVE-2026-42524

Immediate Actions Required

• Update the Jenkins HTML Publisher Plugin to the latest patched version as soon as a fix is available
• Review existing job names for any suspicious content containing script tags or encoded payloads
• Restrict Item/Configure permission to trusted users only
• Enable Content Security Policy headers in Jenkins to mitigate XSS impact

Patch Information

Refer to the Jenkins Security Advisory SECURITY-3706 for official patch information and updated plugin versions. Organizations should update to the patched version of the HTML Publisher Plugin as soon as it becomes available through the Jenkins Update Center.

Workarounds

• Audit and restrict Item/Configure permissions to minimize the attack surface
• Review and sanitize existing job names to remove any potentially malicious content
• Implement strict Content Security Policy headers to prevent inline script execution
• Consider temporarily disabling the HTML Publisher Plugin until a patch can be applied
• Monitor Jenkins logs for any signs of exploitation attempts

# Review Jenkins job configurations for suspicious job names
# Run from Jenkins script console or CLI
# Search for job names containing potential XSS payloads

# Example: List jobs and check for suspicious characters in names
jenkins-cli list-jobs | grep -E "[<>'\"]|script|javascript|onerror|onload"

# Review plugin version - update if version 427 or earlier
jenkins-cli list-plugins | grep "htmlpublisher"