CVE-2021-40358
📋 TL;DR
This is a critical path traversal vulnerability (CWE-22) in Siemens SIMATIC PCS 7 and WinCC systems that allows attackers to bypass directory restrictions and perform unauthorized file operations. Attackers can read, write, or delete critical files on the web server, potentially leading to system compromise. Affected systems include multiple versions of SIMATIC PCS 7 (V8.2, V9.0, V9.1) and WinCC (V7.4, V7.5, V15, V16, V17).
💻 Affected Systems
- SIMATIC PCS 7
- SIMATIC WinCC
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise through arbitrary file write leading to remote code execution, configuration modification, or data destruction.
Likely Case
Unauthorized file access leading to sensitive information disclosure, configuration tampering, or denial of service through file deletion.
If Mitigated
Limited impact if proper network segmentation and access controls prevent exploitation attempts.
🎯 Exploit Status
The vulnerability allows unauthenticated exploitation via web requests. No public exploit code is known, but the vulnerability is straightforward to exploit.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: PCS 7 V9.0 SP3 UC04, V9.1 SP1; WinCC V15 SP1 Update 7, V16 Update 5, V17 Update 2, V7.4 SP1 Update 19, V7.5 SP2 Update 5
Vendor Advisory: https://cert-portal.siemens.com/productcert/pdf/ssa-840188.pdf
Restart Required: Yes
Instructions:
1. Download appropriate updates from Siemens support portal. 2. Apply updates according to Siemens documentation. 3. Restart affected systems. 4. Verify patch installation.
🔧 Temporary Workarounds
Network Segmentation
allRestrict network access to affected web servers to only trusted sources.
Web Application Firewall
allDeploy WAF with rules to detect and block path traversal attempts.
🧯 If You Can't Patch
- Isolate affected systems in separate network segments with strict firewall rules
- Implement strict access controls and monitor for suspicious file operations
🔍 How to Verify
Check if Vulnerable:
Check installed version against affected versions list. Review Siemens advisory for specific version checks.Check Version:
Check version through Siemens management console or product documentationVerify Fix Applied:
Verify installed version matches or exceeds patched versions listed in vendor advisory.📡 Detection & Monitoring
Log Indicators:
- Unusual file access patterns
- Path traversal strings in web logs (../, ..\, %2e%2e%2f)
- Unauthorized file modification attempts
Network Indicators:
- HTTP requests containing path traversal sequences to affected endpoints
- Unusual file operations via web interface
SIEM Query:
web.url:*../* AND (dst.port:80 OR dst.port:443) AND dst.ip:[affected_systems]