CVE-2025-13523
📋 TL;DR
This cross-site scripting (XSS) vulnerability in Mattermost's Confluence plugin allows authenticated Confluence users with malicious display names to execute arbitrary JavaScript in victim browsers. Attackers can send specially crafted OAuth2 connection links that render their display name without proper HTML escaping. Organizations using Mattermost with the Confluence plugin version below 1.7.0 are affected.
💻 Affected Systems
- Mattermost Confluence Plugin
📦 What is this software?
Confluence by Mattermost
⚠️ Risk & Real-World Impact
Worst Case
Attackers could steal session cookies, perform actions as authenticated users, redirect to malicious sites, or deploy ransomware through browser-based attacks.
Likely Case
Attackers steal session tokens to gain unauthorized access to Mattermost/Confluence, potentially accessing sensitive conversations and documents.
If Mitigated
With proper input validation and output encoding, the attack would fail to execute JavaScript, limiting impact to display of unusual characters.
🎯 Exploit Status
Exploitation requires authenticated Confluence access and social engineering to get victims to click malicious OAuth2 links. The XSS payload execution is straightforward once the link is visited.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.7.0 and later
Vendor Advisory: https://mattermost.com/security-updates
Restart Required: Yes
Instructions:
1. Update Mattermost Confluence plugin to version 1.7.0 or higher via Mattermost System Console > Plugins. 2. Restart Mattermost server. 3. Verify plugin version shows 1.7.0+ in System Console.
🔧 Temporary Workarounds
Disable Confluence Plugin
allTemporarily disable the vulnerable plugin until patching is possible
mmctl plugin disable confluence
Restrict Display Name Changes
allLimit Confluence user ability to modify display names to trusted administrators only
🧯 If You Can't Patch
- Implement web application firewall (WAF) rules to block XSS payloads in OAuth2 parameters
- Monitor for unusual display name changes in Confluence audit logs and suspicious OAuth2 connection attempts
🔍 How to Verify
Check if Vulnerable:
Check Mattermost System Console > Plugins > Confluence plugin version. If version is below 1.7.0, system is vulnerable.Check Version:
mmctl plugin list | grep confluenceVerify Fix Applied:
Confirm plugin version shows 1.7.0 or higher in System Console. Test by creating a Confluence user with HTML in display name and attempting OAuth2 connection.📡 Detection & Monitoring
Log Indicators:
- Unusual display name changes in Confluence logs
- Multiple failed OAuth2 connection attempts from same user
- JavaScript execution errors in Mattermost logs
Network Indicators:
- OAuth2 redirects containing script tags or JavaScript in parameters
- Unusual outbound connections from Mattermost server after OAuth2 flows
SIEM Query:
source="mattermost.log" AND "confluence" AND ("oauth2" OR "display_name") AND ("script" OR "javascript" OR "onerror" OR "onload")