CVE-2024-20260 Overview
CVE-2024-20260 is a denial-of-service (DoS) vulnerability affecting the VPN and management web servers of Cisco Adaptive Security Virtual Appliance (ASAv) and Cisco Secure Firewall Threat Defense Virtual (FTDv), formerly Cisco Firepower Threat Defense Virtual. An unauthenticated remote attacker can exhaust system memory by flooding the virtual appliance with new SSL/TLS connections. The condition degrades SSL VPN connection processing until it stops entirely. Cisco published the advisory on October 23, 2024, and the issue maps to improper memory management on incoming TLS sessions [CWE-789].
Critical Impact
A remote, unauthenticated attacker can deplete memory on ASAv and FTDv instances, halting SSL VPN services and forcing a manual reload to restore operations.
Affected Products
- Cisco Adaptive Security Virtual Appliance (ASAv)
- Cisco Secure Firewall Threat Defense Virtual (FTDv)
- Cisco Firepower Threat Defense Virtual (legacy name for FTDv)
Discovery Timeline
- 2024-10-23 - CVE-2024-20260 published to NVD with Cisco Security Advisory cisco-sa-asaftdvirtual-dos-MuenGnYR
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2024-20260
Vulnerability Analysis
The vulnerability resides in how the ASAv and FTDv VPN and management web servers handle new incoming SSL/TLS connections. The platforms fail to enforce proper memory accounting for connection state. As each new TLS session is initiated, allocated memory is not released or capped, allowing unbounded growth. Sustained connection requests drive the device toward memory exhaustion. Once exhausted, the SSL VPN subsystem slows and ultimately stops processing new client connections. Cisco notes that memory may recover slowly after attack traffic stops, but operators typically need a manual reload to return the appliance to a usable state quickly. The flaw is categorized under [CWE-789] (Memory Allocation with Excessive Size Value) and reflects a resource exhaustion condition specific to the virtualized form factors of these platforms.
Root Cause
The root cause is a lack of proper memory management for new SSL/TLS connection state on the virtual platforms. The web server components servicing AnyConnect SSL VPN and the management interface allocate connection resources without sufficient bounds, retention limits, or back-pressure on inbound TLS handshake volume. Physical ASA and FTD appliances are not listed as affected, indicating the defect is specific to the virtual platform memory subsystem.
Attack Vector
Exploitation requires only network reachability to the VPN web server or management web server. No credentials and no user interaction are required. An attacker sends a sustained, high-volume stream of new TLS connection attempts to the listening HTTPS interface. Each connection consumes memory that is not reclaimed at the expected rate, leading to depletion and a DoS condition affecting SSL VPN service availability.
No public exploit code or proof-of-concept has been published for this issue. Refer to the Cisco Security Advisory for full technical context.
Detection Methods for CVE-2024-20260
Indicators of Compromise
- Sustained, abnormally high rate of inbound TLS handshakes to the ASAv or FTDv VPN web server interface (TCP/443) from one or many source IPs.
- Steadily rising memory utilization on the virtual appliance without a corresponding rise in established VPN sessions.
- Failed or slow AnyConnect SSL VPN client connections coinciding with elevated TLS connection counts.
- Syslog entries indicating memory allocation failures or web server resource exhaustion on ASAv/FTDv.
Detection Strategies
- Baseline normal TLS connection rates per source IP and alert on anomalous spikes against the VPN and management web servers.
- Correlate appliance SNMP memory metrics with TLS connection counters to identify divergence indicative of leak-like growth.
- Inspect connection logs for repeated half-open or short-lived TLS sessions from the same client subnets.
Monitoring Recommendations
- Continuously poll show memory and show conn count equivalents on ASAv/FTDv and export to a centralized monitoring system.
- Forward ASAv and FTDv syslogs to a SIEM or data lake and alert on web server, TLS, and memory subsystem warnings.
- Monitor SSL VPN login success rates and AnyConnect client error telemetry for early service degradation signals.
How to Mitigate CVE-2024-20260
Immediate Actions Required
- Apply the fixed software releases listed in the Cisco Security Advisory cisco-sa-asaftdvirtual-dos-MuenGnYR for ASAv and FTDv.
- Restrict access to the management web server to trusted administrative networks only.
- Place rate-limiting or DDoS protection in front of public-facing SSL VPN endpoints to cap new TLS connection rates.
- Establish an incident runbook to reload affected ASAv or FTDv instances quickly if memory exhaustion occurs.
Patch Information
Cisco has released fixed software versions for ASAv and FTDv. Consult the Cisco Security Advisory for the specific fixed releases that correspond to each deployed train. No workarounds that fully remediate the defect are listed by Cisco; upgrading is the recommended path.
Workarounds
- Apply infrastructure access control lists (iACLs) and control plane protections to limit who can initiate TLS connections to the VPN and management interfaces.
- Use an upstream load balancer, WAF, or DDoS mitigation service to enforce per-source TLS connection rate limits.
- Disable the management web server on interfaces that do not require remote administration.
- Segment management traffic onto a dedicated, restricted network reachable only from administrative jump hosts.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
