CVE-2021-34584
📋 TL;DR
CVE-2021-34584 is a buffer over-read vulnerability in the CODESYS V2 web server that allows attackers to read partial stack or heap memory or cause denial-of-service through crafted web requests. This affects industrial control systems using CODESYS V2 web server prior to version 1.1.9.22. Organizations using CODESYS automation software with exposed web interfaces are at risk.
💻 Affected Systems
- CODESYS V2 web server
📦 What is this software?
Codesys by Codesys
⚠️ Risk & Real-World Impact
Worst Case
Information disclosure of sensitive memory contents including credentials, configuration data, or process information, potentially leading to further system compromise.
Likely Case
Denial-of-service through web server crashes disrupting industrial control system operations and availability.
If Mitigated
Limited impact if web server is isolated behind firewalls with restricted network access and proper segmentation.
🎯 Exploit Status
Tenable Research published technical details and proof-of-concept; exploitation requires sending crafted HTTP requests to vulnerable web server.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: V1.1.9.22
Vendor Advisory: https://customers.codesys.com/index.php?eID=dumpFile&t=f&f=16876&token=a3f1d937f95e7034879f4f2ea8e5a99b168256a7&download=
Restart Required: Yes
Instructions:
1. Download CODESYS V2 web server version 1.1.9.22 or later from CODESYS customer portal. 2. Backup current configuration. 3. Install the update following vendor instructions. 4. Restart the web server service. 5. Verify successful update.
🔧 Temporary Workarounds
Network segmentation and access control
allRestrict network access to CODESYS web server using firewalls and network segmentation
Disable web server if not required
allTurn off CODESYS V2 web server component if not needed for operations
🧯 If You Can't Patch
- Implement strict network segmentation to isolate CODESYS systems from untrusted networks
- Deploy web application firewall (WAF) rules to block suspicious HTTP requests patterns
🔍 How to Verify
Check if Vulnerable:
Check CODESYS web server version via web interface or configuration files; versions below 1.1.9.22 are vulnerable.Check Version:
Check CODESYS configuration or web interface for version information; specific command varies by installation.Verify Fix Applied:
Verify installed version is 1.1.9.22 or higher and test web server functionality remains operational.📡 Detection & Monitoring
Log Indicators:
- Unusual HTTP request patterns to CODESYS web server
- Web server crash/restart events in system logs
- Memory access errors in application logs
Network Indicators:
- Crafted HTTP requests with abnormal parameters or lengths to CODESYS web server port (typically 80/443)
SIEM Query:
source="codesys_webserver" AND (http_request_length>threshold OR http_uri_contains_suspicious_patterns)🔗 References
- https://customers.codesys.com/index.php?eID=dumpFile&t=f&f=16876&token=a3f1d937f95e7034879f4f2ea8e5a99b168256a7&download=
- https://www.tenable.com/security/research/tra-2021-47
- https://customers.codesys.com/index.php?eID=dumpFile&t=f&f=16876&token=a3f1d937f95e7034879f4f2ea8e5a99b168256a7&download=
- https://www.tenable.com/security/research/tra-2021-47
