CVE-2026-20006
📋 TL;DR
A TLS implementation vulnerability in Cisco Secure Firewall Threat Defense Software allows remote attackers to trigger a Snort 3 Detection Engine restart by sending crafted TLS packets, causing denial of service. Only systems running affected Cisco FTD software with TLS 1.2 or earlier are vulnerable. TLS 1.3 is not affected.
💻 Affected Systems
- Cisco Secure Firewall Threat Defense (FTD) Software
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Continuous exploitation could cause repeated Snort 3 restarts, leading to sustained traffic inspection failure and network disruption until manual intervention.
Likely Case
Intermittent Snort 3 restarts causing brief traffic inspection gaps and potential packet loss until the attack stops or system is patched.
If Mitigated
With proper network segmentation and TLS 1.3 enforcement, impact is limited to isolated network segments with minimal service disruption.
🎯 Exploit Status
Exploitation requires sending crafted TLS packets to vulnerable systems, which is relatively straightforward for attackers with network access.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Cisco advisory for specific fixed versions
Vendor Advisory: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-tcp-dos-rHfqnwRg
Restart Required: Yes
Instructions:
1. Review Cisco advisory for affected versions. 2. Download and apply appropriate patch from Cisco. 3. Restart affected FTD services or devices. 4. Verify patch application and monitor for stability.
🔧 Temporary Workarounds
Enforce TLS 1.3 Only
allConfigure affected systems to only accept TLS 1.3 connections, as the vulnerability only affects TLS 1.2 and earlier.
# Configure TLS 1.3 only in FTD policy
# Refer to Cisco documentation for specific configuration commands
Network Segmentation
allRestrict access to FTD management interfaces and TLS endpoints to trusted networks only.
# Implement ACLs to restrict TLS access
# Example: access-list TLS-RESTRICT extended deny tcp any any eq 443
access-list TLS-RESTRICT extended permit tcp trusted-networks any eq 443
🧯 If You Can't Patch
- Implement strict network access controls to limit TLS traffic to trusted sources only
- Deploy intrusion prevention systems to detect and block crafted TLS packets targeting this vulnerability
🔍 How to Verify
Check if Vulnerable:
Check Cisco FTD software version against affected versions listed in Cisco advisory. Verify if TLS 1.2 or earlier is enabled.Check Version:
show version | include VersionVerify Fix Applied:
After patching, verify software version is updated and test with legitimate TLS traffic to ensure Snort 3 remains stable.📡 Detection & Monitoring
Log Indicators:
- Repeated Snort 3 process restarts in system logs
- Increased 'engine restart' or 'process died' messages in FTD logs
- Unusual TLS handshake failures or malformed packet alerts
Network Indicators:
- Abnormal TLS packet patterns targeting FTD systems
- Sudden drops in inspected traffic volume
- Increased TCP retransmissions to/through FTD
SIEM Query:
source="cisco-ftd" AND ("Snort restart" OR "engine died" OR "process terminated")