CISCO Security Advisory
Published Date: Not specified
CVE: CVE-2026-20154
Advisory Summary
🗓️ Calendar: Sep 18, 2026
🚨 Adaptive Security Appliance / Threat Defense DoS via Syslog Rate-Limiting
- Cisco Secure Firewall Adaptive Security Appliance (ASA) Software
- Cisco Secure Firewall Threat Defense (FTD) Software
An unauthenticated remote attacker can exploit improper rate limiting to drive high CPU utilization, causing denial of service (DoS) and overall performance degradation.
- The attacker sends a flood of TCP SYN packets to the affected device.
- This triggers excessive processing tied to syslog message 419002, overwhelming CPU resources.
- Availability impact: Potential service disruption for security policy enforcement, sessions, VPN/inspection workloads.
- Detection complexity: May resemble volumetric traffic or noisy log-processing behavior; impact may be mistaken for congestion under attack.
- Exposure likelihood: Remote, unauthenticated vector increases probability of opportunistic scanning/exploitation.
- Apply Cisco software updates addressing the vulnerability (Cisco states updates are available).
- Implement the provided workarounds from the advisory if immediate patching is not possible.
- Review exposure paths where TCP SYN floods can reach the firewall (ingress interfaces, upstream load balancers, edge ACLs).
🔎 Immediate recommendations for security teams
1. Patch ASAP for ASA/FTD versions listed by Cisco for CVE-2026-20154.
2. Add/verify protections against SYN flood and abusive connection attempts (edge filtering, rate limits, upstream DDoS controls).
3. Monitor for CPU spikes correlated with traffic surges and syslog activity around message 419002.
4. Validate logging/syslog configurations—ensure they align with Cisco hardening guidance.
-2026-20154
Reference: Vendor Advisory