CVE-2021-26788
📋 TL;DR
CVE-2021-26788 is an incorrect input validation vulnerability in Oryx Embedded CycloneTCP that allows unauthenticated attackers to cause denial of service (DoS) by sending malicious TCP packets. Systems running affected versions of CycloneTCP with TCP connectivity to untrusted networks are vulnerable. The vulnerability requires TCP connectivity to the target but no authentication.
💻 Affected Systems
- Oryx Embedded CycloneTCP
📦 What is this software?
Cyclonetcp by Oryx Embedded
⚠️ Risk & Real-World Impact
Worst Case
Complete service disruption of affected network services, potentially requiring system restart to recover functionality.
Likely Case
Service interruption affecting TCP-based communications, causing application downtime until the affected service is restarted.
If Mitigated
Limited impact with proper network segmentation and filtering, potentially no service disruption if malicious packets are blocked.
🎯 Exploit Status
Exploitation requires only TCP connectivity and sending a crafted packet. No authentication or special privileges needed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.0.2
Vendor Advisory: https://github.com/Oryx-Embedded/CycloneTCP/commit/de5336016edbe1e90327d0ed1cba5c4e49114366
Restart Required: Yes
Instructions:
1. Update CycloneTCP library to version 2.0.2 or later. 2. Recompile applications using the library. 3. Restart affected services or systems.
🔧 Temporary Workarounds
Network Filtering
allBlock or filter malicious TCP packets at network perimeter using firewall rules or intrusion prevention systems.
Service Isolation
allSegment network to restrict TCP access to vulnerable systems only from trusted sources.
🧯 If You Can't Patch
- Implement strict network access controls to limit TCP connectivity to trusted sources only.
- Deploy network-based intrusion prevention systems to detect and block malicious TCP packets.
🔍 How to Verify
Check if Vulnerable:
Check if CycloneTCP library version is between 1.7.6 and 2.0.0 inclusive. Review application dependencies and build configurations.Check Version:
Check build configuration files or application documentation for CycloneTCP version. For embedded systems, consult vendor documentation.Verify Fix Applied:
Verify CycloneTCP library version is 2.0.2 or later. Test TCP connectivity and service stability under normal and stress conditions.📡 Detection & Monitoring
Log Indicators:
- Unexpected service crashes
- TCP connection resets
- Increased error rates in TCP stack logs
Network Indicators:
- Malformed TCP packets targeting vulnerable systems
- Sudden increase in TCP reset packets
SIEM Query:
source="network_firewall" AND (tcp.flags.reset=1 OR tcp.malformed=true) AND dest_ip="[vulnerable_system]"🔗 References
- https://github.com/Oryx-Embedded/CycloneTCP/commit/de5336016edbe1e90327d0ed1cba5c4e49114366?branch=de5336016edbe1e90327d0ed1cba5c4e49114366&diff=split
- https://github.com/Oryx-Embedded/CycloneTCP/commit/de5336016edbe1e90327d0ed1cba5c4e49114366?branch=de5336016edbe1e90327d0ed1cba5c4e49114366&diff=split
