CVE-2026-20013: Cisco Secure Firewall IKEv2 DoS Vulnerability

CVE-2026-20013 Overview

A vulnerability in the IKEv2 feature of Cisco Secure Firewall ASA Software and Cisco Secure FTD Software could allow an unauthenticated, remote attacker to cause a Denial of Service (DoS) condition on an affected device. This memory exhaustion vulnerability may also impact the availability of services to devices elsewhere in the network, creating cascading service disruptions across the infrastructure.

Critical Impact

Unauthenticated remote attackers can exhaust device memory through crafted IKEv2 packets, causing a DoS condition that requires manual device reload to recover.

Affected Products

• Cisco Secure Firewall ASA Software (with IKEv2 enabled)
• Cisco Secure Firewall FTD Software (with IKEv2 enabled)
• Network devices dependent on affected firewall services

Discovery Timeline

• 2026-03-04 - CVE-2026-20013 published to NVD
• 2026-03-05 - Last updated in NVD database

Technical Details for CVE-2026-20013

Vulnerability Analysis

This vulnerability (CWE-401: Missing Release of Memory after Effective Lifetime) stems from improper memory management during IKEv2 packet processing. When the affected device processes IKEv2 packets, allocated memory is not properly freed after use, leading to progressive memory exhaustion. The network-based attack requires no authentication or user interaction, allowing remote attackers to target any exposed IKEv2 service. While the scope is changed (meaning the vulnerability can impact resources beyond the vulnerable component), the primary impact is on availability with no direct confidentiality or integrity compromise. The eventual resource exhaustion necessitates manual device reload for recovery, creating significant operational disruption.

Root Cause

The root cause is a memory leak (CWE-401) in the IKEv2 packet processing code path. When IKEv2 packets are received and processed by the affected Cisco Secure Firewall ASA or FTD Software, memory allocated for packet handling is not properly released after the processing completes. Over time, this causes cumulative memory exhaustion as each processed packet consumes additional memory that is never reclaimed.

Attack Vector

The attack is executed remotely over the network without requiring authentication. An attacker sends specially crafted IKEv2 packets to an affected device with IKEv2 services enabled. Each malicious packet triggers memory allocation that is never freed, progressively depleting available system memory. As memory resources become exhausted, the device enters a degraded state and eventually becomes unresponsive, requiring manual intervention to reload the device and restore normal operation.

The vulnerability can be exploited by sending a sustained stream of crafted IKEv2 packets to UDP port 500 or 4500 on an affected device. The attack does not require successful IKEv2 session establishment—the memory leak occurs during initial packet processing. For detailed technical information about this vulnerability, refer to the Cisco Security Advisory.

Detection Methods for CVE-2026-20013

Indicators of Compromise

• Abnormal memory utilization patterns on Cisco ASA or FTD devices with gradual, consistent memory growth
• Increased volume of IKEv2 packets from unexpected source IP addresses
• Device performance degradation or unresponsiveness following periods of elevated IKEv2 traffic
• System logs indicating memory allocation failures or resource exhaustion warnings

Detection Strategies

• Monitor memory utilization trends on affected devices using show memory and show blocks commands
• Implement IDS/IPS rules to detect anomalous IKEv2 packet patterns or excessive connection attempts
• Configure SNMP traps for memory threshold alerts on Cisco ASA/FTD devices
• Deploy network traffic analysis to identify unusual spikes in UDP port 500/4500 traffic

Monitoring Recommendations

• Establish baseline memory utilization metrics and alert on deviations exceeding normal operational thresholds
• Enable detailed logging for IKEv2 subsystem events and review for anomalous patterns
• Implement continuous availability monitoring for VPN services dependent on IKEv2
• Configure automated alerting for device reload events that may indicate exploitation attempts

How to Mitigate CVE-2026-20013

Immediate Actions Required

• Review the Cisco Security Advisory for specific affected versions and patch availability
• Identify all Cisco ASA and FTD devices with IKEv2 enabled in your environment
• Implement access control lists (ACLs) to restrict IKEv2 traffic to known, trusted IP addresses
• Schedule maintenance windows to apply vendor patches when available

Patch Information

Cisco has released security updates to address this vulnerability. Administrators should consult the Cisco Security Advisory for specific fixed software versions and upgrade instructions applicable to their deployment. Ensure devices are running a supported software version before applying the security patch.

Workarounds

• Restrict IKEv2 access using access control lists to limit connections to trusted IP addresses only
• If IKEv2 is not required, consider disabling the feature and using alternative VPN protocols
• Implement rate limiting for IKEv2 connections to reduce the impact of potential exploitation attempts
• Deploy network segmentation to isolate affected devices and limit the scope of potential service disruption

# Example ACL configuration to restrict IKEv2 access (adjust IP ranges as needed)
access-list OUTSIDE_IN extended permit udp host <trusted-peer-ip> any eq isakmp
access-list OUTSIDE_IN extended permit udp host <trusted-peer-ip> any eq 4500
access-list OUTSIDE_IN extended deny udp any any eq isakmp log
access-list OUTSIDE_IN extended deny udp any any eq 4500 log