CVE-2025-51691
📋 TL;DR
A Cross-Site Scripting (XSS) vulnerability in MarkTwo Markdown Editor allows attackers to inject malicious scripts through user-supplied Markdown content. When victims view the malicious content, attackers can execute arbitrary JavaScript in their browsers, potentially stealing credentials or hijacking sessions. This affects all users of MarkTwo who process untrusted Markdown input.
💻 Affected Systems
- MarkTwo Markdown Editor
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Complete account takeover, credential theft, and client-side malware deployment affecting all users who view malicious content.
Likely Case
Session hijacking and credential theft from users who interact with crafted Markdown content.
If Mitigated
Limited impact with proper input validation and output encoding, potentially preventing script execution.
🎯 Exploit Status
Exploitation requires user interaction with malicious content but doesn't require authentication.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Commit after e3a1d3f90cce4ea9c26efcbbf3a1cbfb9dcdb298
Vendor Advisory: https://github.com/anthonygarvan/marktwo
Restart Required: No
Instructions:
1. Update to latest MarkTwo version from GitHub. 2. Replace vulnerable commit with patched version. 3. Test Markdown sanitization functionality.
🔧 Temporary Workarounds
Input Sanitization
allImplement server-side sanitization of all Markdown input before processing.
Content Security Policy
allImplement strict CSP headers to prevent script execution from untrusted sources.
🧯 If You Can't Patch
- Disable Markdown processing for untrusted users
- Implement web application firewall with XSS protection rules
🔍 How to Verify
Check if Vulnerable:
Test by injecting script tags in Markdown input and checking if they execute in rendered output.Check Version:
git log --oneline | head -1Verify Fix Applied:
Verify that script injections in Markdown are properly sanitized and don't execute.📡 Detection & Monitoring
Log Indicators:
- Unusual Markdown input patterns
- Multiple failed sanitization attempts
Network Indicators:
- Suspicious script tags in HTTP POST requests to editor endpoints
SIEM Query:
source="web_logs" AND ("<script>" OR "javascript:") AND uri_path="/editor"