CVE-2026-23769
📋 TL;DR
This vulnerability in lucy-xss-filter allows attackers to execute malicious JavaScript through cross-site scripting (XSS) attacks due to improper sanitization from misconfigured default superset rule files. It affects applications using vulnerable versions of the lucy-xss-filter library for input sanitization. The impact is limited to applications that process user input through this library.
💻 Affected Systems
- lucy-xss-filter
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Attackers could steal user sessions, redirect users to malicious sites, deface websites, or perform actions on behalf of authenticated users.
Likely Case
Attackers inject malicious scripts that steal session cookies or user data from vulnerable web applications.
If Mitigated
With proper input validation and output encoding, the impact is limited to specific contexts where lucy-xss-filter is the sole sanitization method.
🎯 Exploit Status
Exploitation requires user input to reach vulnerable sanitization functions.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Commit e5826c0 or later
Vendor Advisory: https://github.com/naver/lucy-xss-filter/pull/32
Restart Required: No
Instructions:
1. Update lucy-xss-filter to commit e5826c0 or later. 2. Verify the fix by checking the commit hash. 3. Test application functionality after update.
🔧 Temporary Workarounds
Implement additional input validation
allAdd custom input validation before lucy-xss-filter processing
Use alternative XSS protection
allImplement output encoding or use different XSS filtering libraries
🧯 If You Can't Patch
- Implement strict Content Security Policy (CSP) headers
- Deploy WAF rules to detect and block XSS payloads
🔍 How to Verify
Check if Vulnerable:
Check if lucy-xss-filter version is before commit e5826c0 in package.json or dependency filesCheck Version:
grep -r "lucy-xss-filter" package.json || check project dependenciesVerify Fix Applied:
Verify commit hash includes e5826c0 or later in the lucy-xss-filter repository📡 Detection & Monitoring
Log Indicators:
- Unusual script tags in input logs
- Multiple failed sanitization attempts
Network Indicators:
- Suspicious JavaScript payloads in HTTP requests
SIEM Query:
web_requests WHERE request_body CONTAINS '<script>' OR request_body CONTAINS 'javascript:'