CVE-2021-23856
📋 TL;DR
This vulnerability allows attackers to execute malicious scripts in users' browsers by tricking them into clicking specially crafted URLs. It affects Bosch Rexroth ctrlX CORE and ctrlX COREvirtual devices running vulnerable firmware versions. The attack requires user interaction but can lead to session hijacking or credential theft.
💻 Affected Systems
- Bosch Rexroth ctrlX CORE
- Bosch Rexroth ctrlX COREvirtual
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of user sessions, credential theft, administrative account takeover, and lateral movement within the network.
Likely Case
Session hijacking, credential theft, and unauthorized actions performed in the context of the victim user.
If Mitigated
Limited impact if proper input validation and output encoding are implemented, though some risk remains if users click malicious links.
🎯 Exploit Status
Reflected XSS typically requires user interaction but is straightforward to exploit once a malicious URL is crafted.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Firmware V1.5 or later
Vendor Advisory: https://psirt.bosch.com/security-advisories/bosch-sa-741752.html
Restart Required: Yes
Instructions:
1. Download firmware V1.5 or later from Bosch Rexroth support portal. 2. Backup device configuration. 3. Apply firmware update via web interface or local update method. 4. Verify successful update and restore configuration if needed.
🔧 Temporary Workarounds
Input Validation Filter
allImplement server-side input validation to sanitize URL parameters before processing.
Not applicable - requires code changes
Content Security Policy
allImplement CSP headers to restrict script execution sources.
Content-Security-Policy: default-src 'self'; script-src 'self'
🧯 If You Can't Patch
- Implement network segmentation to isolate affected devices from untrusted networks
- Deploy web application firewall with XSS protection rules
🔍 How to Verify
Check if Vulnerable:
Test web interface with XSS payloads in URL parameters (e.g., <script>alert('XSS')</script>)Check Version:
Check firmware version in web interface under System Information or via SSH: cat /etc/ctrlx-versionVerify Fix Applied:
Verify firmware version is V1.5 or later and retest with XSS payloads to confirm they are properly sanitized📡 Detection & Monitoring
Log Indicators:
- Unusual URL parameters containing script tags or JavaScript code
- Multiple failed login attempts from same IP
Network Indicators:
- HTTP requests with suspicious parameters containing <script> tags or JavaScript functions
SIEM Query:
web.url:*<script>* OR web.url:*javascript:*