CVE-2026-21855
📋 TL;DR
CVE-2026-21855 is a reflected Cross-Site Scripting (XSS) vulnerability in Tarkov Data Manager's toast notification system that allows attackers to execute arbitrary JavaScript in victims' browsers via malicious URLs. This affects all users running versions prior to the January 2, 2025 fixes. Attackers can steal session cookies, redirect users, or perform actions on their behalf.
💻 Affected Systems
- Tarkov Data Manager
⚠️ Risk & Real-World Impact
Worst Case
Complete account takeover, session hijacking, credential theft, and potential malware delivery to all users accessing malicious links.
Likely Case
Session hijacking leading to unauthorized access to user data and potential manipulation of Tarkov item data managed through the application.
If Mitigated
Limited impact with proper input validation, output encoding, and Content Security Policy (CSP) headers in place.
🎯 Exploit Status
Reflected XSS vulnerabilities are commonly exploited via phishing or malicious links. No public exploit code is mentioned in the advisory.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Versions with commits from January 2, 2025
Vendor Advisory: https://github.com/the-hideout/tarkov-data-manager/security/advisories/GHSA-9c23-rrg9-jc89
Restart Required: Yes
Instructions:
1. Update to the latest version of Tarkov Data Manager. 2. Apply all security patches from January 2, 2025. 3. Restart the application service. 4. Verify the fix by testing XSS payloads.
🔧 Temporary Workarounds
Implement Content Security Policy
allAdd CSP headers to restrict script execution sources
Add 'Content-Security-Policy: script-src 'self'' to web server headers
Input Validation Filter
allAdd server-side validation for toast notification parameters
Implement parameter sanitization in the toast notification handler
🧯 If You Can't Patch
- Implement Web Application Firewall (WAF) rules to block XSS payloads in URL parameters
- Disable or restrict access to the vulnerable toast notification endpoint if not critical
🔍 How to Verify
Check if Vulnerable:
Test by injecting basic XSS payloads into toast notification parameters (e.g., <script>alert('XSS')</script>) and checking if they execute.Check Version:
Check application version or commit hash against January 2, 2025 fixesVerify Fix Applied:
Attempt the same XSS payloads after patching; they should be properly encoded or rejected.📡 Detection & Monitoring
Log Indicators:
- Unusual long parameter values in toast notification requests
- Requests containing script tags or JavaScript code in URL parameters
Network Indicators:
- HTTP requests with suspicious parameters containing script tags or JavaScript functions
SIEM Query:
source="web_logs" AND (uri="*toast*" AND (param="*<script>*" OR param="*javascript:*"))