CVE-2023-1776
📋 TL;DR
This vulnerability allows attackers to upload malicious SVG files to Mattermost Boards and share them via direct links. When users view these SVG files, cross-site scripting (XSS) attacks can execute in their browsers. All Mattermost Boards users are potentially affected.
💻 Affected Systems
- Mattermost Boards
📦 What is this software?
Mattermost Server by Mattermost
Mattermost Server by Mattermost
⚠️ Risk & Real-World Impact
Worst Case
Attackers could steal session cookies, perform actions as authenticated users, or redirect users to malicious sites, potentially leading to account compromise and data theft.
Likely Case
Attackers would typically use this for session hijacking, credential theft, or delivering malware through malicious redirects.
If Mitigated
With proper content security policies and file upload restrictions, impact would be limited to isolated XSS within the SVG viewer context.
🎯 Exploit Status
Requires attacker to have upload permissions and ability to share direct links.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Mattermost security updates for specific version
Vendor Advisory: https://mattermost.com/security-updates/
Restart Required: Yes
Instructions:
1. Check Mattermost security advisory for patched version. 2. Update Mattermost Boards to the patched version. 3. Restart the Mattermost service.
🔧 Temporary Workarounds
Disable SVG uploads
allConfigure Mattermost to block SVG file uploads entirely
Configure FileSettings.ExtensionRestrictions in config.json to include 'svg'
Restrict direct file links
allDisable or restrict the direct link sharing feature for attachments
Configure appropriate permissions in Mattermost settings
🧯 If You Can't Patch
- Implement strict Content Security Policy headers to mitigate XSS impact
- Monitor for SVG file uploads and investigate suspicious activity
🔍 How to Verify
Check if Vulnerable:
Check if your Mattermost Boards version is before the patched version listed in the security advisoryCheck Version:
Check Mattermost System Console → About → VersionVerify Fix Applied:
Verify you're running the patched version and test SVG upload functionality📡 Detection & Monitoring
Log Indicators:
- Unusual SVG file uploads
- Multiple SVG uploads from single user
- Direct link access to SVG files
Network Indicators:
- Requests to SVG files with suspicious parameters
- External calls from SVG content
SIEM Query:
source="mattermost" AND (file_extension="svg" OR file_type="image/svg+xml")