CVE-2025-66500
📋 TL;DR
A stored cross-site scripting vulnerability in webplugins.foxit.com allows attackers to inject malicious JavaScript via postMessage. This affects users who visit the compromised Foxit web plugin interface. Attackers can steal session cookies, redirect users, or perform actions on their behalf.
💻 Affected Systems
- Foxit web plugins
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete account takeover, data theft, or malware distribution to all users accessing the vulnerable interface.
Likely Case
Session hijacking, credential theft, or unauthorized actions performed in user context.
If Mitigated
Limited impact with proper CSP headers and input validation, potentially only affecting specific plugin functionality.
🎯 Exploit Status
Exploitation requires crafting malicious postMessage payloads but doesn't require authentication to the target system.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown - check vendor advisory
Vendor Advisory: https://www.foxit.com/support/security-bulletins.html
Restart Required: No
Instructions:
1. Visit Foxit security bulletins page 2. Identify relevant patch for web plugins 3. Apply update to web plugin components 4. Verify postMessage origin validation is implemented
🔧 Temporary Workarounds
Implement Content Security Policy
allAdd strict CSP headers to prevent script execution from untrusted sources
Content-Security-Policy: script-src 'self'
PostMessage Origin Validation
allAdd origin validation to postMessage handlers before processing messages
if (event.origin !== 'https://expected-domain.com') return;
🧯 If You Can't Patch
- Block access to webplugins.foxit.com at network perimeter
- Implement WAF rules to detect and block XSS payloads in postMessage traffic
🔍 How to Verify
Check if Vulnerable:
Test if postMessage handlers accept messages from arbitrary origins without validationCheck Version:
Check web plugin version in browser developer tools or contact Foxit supportVerify Fix Applied:
Verify postMessage handlers now validate message.origin before processing📡 Detection & Monitoring
Log Indicators:
- Unusual postMessage activity
- JavaScript errors related to externalPath
Network Indicators:
- Suspicious postMessage payloads in web traffic
- Requests to unexpected script sources
SIEM Query:
web.logs contains 'postMessage' AND (contains 'externalPath' OR contains 'eval' OR contains 'document.write')