CVE-2019-18792
📋 TL;DR
This vulnerability allows attackers to bypass TCP-based intrusion detection signatures in Suricata by injecting fake FIN packets that overlap legitimate TCP segments. Systems running vulnerable versions of Suricata for network monitoring are affected, potentially allowing malicious traffic to evade detection.
💻 Affected Systems
- Suricata
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Attackers completely bypass network intrusion detection, allowing malware delivery, data exfiltration, or command and control traffic to go undetected.
Likely Case
Targeted evasion of specific detection rules, enabling limited malicious activity to bypass security monitoring.
If Mitigated
With proper patching and monitoring, the vulnerability has minimal impact as detection capabilities remain intact.
🎯 Exploit Status
Exploitation requires network access and ability to craft TCP packets with specific timing and sequence numbers.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 5.0.1 and later
Vendor Advisory: https://redmine.openinfosecfoundation.org/issues/3324
Restart Required: Yes
Instructions:
1. Update Suricata to version 5.0.1 or later. 2. Download from official Suricata repositories. 3. Install the updated package. 4. Restart Suricata service.
🔧 Temporary Workarounds
Enable stream.reassembly.depth
allIncrease TCP stream reassembly depth to make overlapping packet evasion more difficult
stream.reassembly.depth: 10mb
🧯 If You Can't Patch
- Deploy additional network monitoring layers (secondary IDS/IPS)
- Implement strict network segmentation to limit attack surface
🔍 How to Verify
Check if Vulnerable:
Check Suricata version with 'suricata --build-info' or 'suricata -V'Check Version:
suricata -VVerify Fix Applied:
Verify version is 5.0.1 or later and check for commit 1c63d3905852f746ccde7e2585600b2199cefb4b in build📡 Detection & Monitoring
Log Indicators:
- Unusual TCP FIN packet patterns
- Signature bypass alerts
- Stream reassembly errors
Network Indicators:
- TCP packets with overlapping sequence numbers
- FIN packets without ACK flag set
SIEM Query:
source="suricata" AND (event_type="alert" AND alert.signature="*bypass*" OR stream.reassembly.error="*")🔗 References
- https://github.com/OISF/suricata/commit/1c63d3905852f746ccde7e2585600b2199cefb4b
- https://github.com/OISF/suricata/commit/fa692df37a796c3330c81988d15ef1a219afc006
- https://lists.debian.org/debian-lts-announce/2020/01/msg00032.html
- https://redmine.openinfosecfoundation.org/issues/3324
- https://redmine.openinfosecfoundation.org/issues/3394
- https://github.com/OISF/suricata/commit/1c63d3905852f746ccde7e2585600b2199cefb4b
- https://github.com/OISF/suricata/commit/fa692df37a796c3330c81988d15ef1a219afc006
- https://lists.debian.org/debian-lts-announce/2020/01/msg00032.html
- https://redmine.openinfosecfoundation.org/issues/3324
- https://redmine.openinfosecfoundation.org/issues/3394
