CVE-2025-13523 Overview
CVE-2025-13523 is a Cross-Site Scripting (XSS) vulnerability affecting the Mattermost Confluence plugin in versions prior to 1.7.0. The vulnerability exists due to improper escaping of user-controlled display names in HTML template rendering, allowing authenticated Confluence users with malicious display names to execute arbitrary JavaScript in victim browsers. Exploitation requires sending a specially crafted OAuth2 connection link that, when visited by a victim, renders the attacker's display name without proper sanitization.
Critical Impact
Authenticated attackers can execute arbitrary JavaScript code in victim browsers, potentially enabling session hijacking, credential theft, or unauthorized actions on behalf of the victim user.
Affected Products
- Mattermost Confluence plugin versions prior to 1.7.0
Discovery Timeline
- 2026-02-06 - CVE CVE-2025-13523 published to NVD
- 2026-02-06 - Last updated in NVD database
Technical Details for CVE-2025-13523
Vulnerability Analysis
This vulnerability is classified as CWE-79 (Improper Neutralization of Input During Web Page Generation), commonly known as Cross-Site Scripting. The flaw resides in how the Mattermost Confluence plugin processes and renders user display names within HTML templates. When authenticated Confluence users craft malicious display names containing JavaScript payloads, the plugin fails to properly sanitize or escape these values before inserting them into the rendered HTML output.
The attack requires user interaction, as victims must click on a specially crafted OAuth2 connection link. Once the link is visited, the attacker's malicious display name is rendered in the victim's browser context without adequate sanitization, causing the embedded JavaScript to execute. This represents a stored/reflected XSS hybrid attack vector that can compromise user sessions across different browser contexts.
Root Cause
The root cause is insufficient output encoding in the HTML template rendering engine used by the Mattermost Confluence plugin. User-controlled display names are inserted directly into HTML templates without proper escaping of special characters such as <, >, ", and '. This allows attackers to break out of the intended HTML context and inject executable script content.
Attack Vector
The attack is network-based and requires the following conditions:
- The attacker must have an authenticated account in Confluence
- The attacker sets their display name to contain malicious JavaScript payload
- The attacker crafts and distributes a specially crafted OAuth2 connection link
- A victim user must click the malicious link
- Upon visiting the link, the plugin renders the attacker's display name, executing the JavaScript payload in the victim's browser
The vulnerability allows the attacker to execute scripts with the same privileges as the victim user, potentially leading to session theft, data exfiltration, or further attack propagation.
Detection Methods for CVE-2025-13523
Indicators of Compromise
- Unusual display names in Confluence user profiles containing HTML tags, JavaScript keywords like script, onerror, onload, or encoded variants
- OAuth2 connection links shared via messaging platforms or email containing suspicious parameters
- Browser console errors or unexpected script execution when interacting with Mattermost Confluence plugin features
- Network requests to external domains originating from Confluence/Mattermost plugin contexts
Detection Strategies
- Implement Content Security Policy (CSP) headers to detect and block unauthorized inline script execution
- Monitor application logs for OAuth2 connection requests with unusual referrers or parameters
- Deploy web application firewalls (WAF) with rules to detect XSS patterns in user-submitted data
- Audit user display names in Confluence for suspicious characters or encoded payloads
Monitoring Recommendations
- Enable verbose logging for the Mattermost Confluence plugin to capture rendering activities
- Monitor for changes to user profile display names, especially those containing special characters
- Implement browser-side XSS detection tools to identify script injection attempts
- Review OAuth2 token generation and connection link patterns for anomalies
How to Mitigate CVE-2025-13523
Immediate Actions Required
- Upgrade the Mattermost Confluence plugin to version 1.7.0 or later immediately
- Review Confluence user accounts for display names containing suspicious HTML or JavaScript content
- Implement Content Security Policy headers to mitigate potential exploitation
- Educate users about the risks of clicking untrusted OAuth2 connection links
Patch Information
Mattermost has addressed this vulnerability in Confluence plugin version 1.7.0. Organizations should update to the patched version as soon as possible. For detailed patch information, refer to the Mattermost Security Updates page. The vulnerability is tracked under Mattermost Advisory ID: MMSA-2025-00557.
Workarounds
- Temporarily disable the Mattermost Confluence plugin until patching is complete
- Implement strict input validation on user display name fields at the Confluence level
- Deploy a web application firewall with XSS protection rules in front of affected systems
- Restrict OAuth2 connection link generation to trusted administrators only
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
