CVE-2026-20015 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 leak vulnerability is triggered when parsing IKEv2 packets, potentially impacting the availability of services to devices elsewhere in the network.
The vulnerability is classified as CWE-401 (Missing Release of Memory after Effective Lifetime), indicating that the affected software fails to properly release memory resources after processing IKEv2 packets.
Critical Impact
Successful exploitation allows attackers to exhaust device memory resources remotely without authentication, eventually requiring a manual device reload to restore functionality.
Affected Products
- Cisco Secure Firewall ASA Software (with IKEv2 enabled)
- Cisco Secure FTD Software (with IKEv2 enabled)
- Network devices dependent on affected ASA/FTD for VPN services
Discovery Timeline
- 2026-03-04 - CVE-2026-20015 published to NVD
- 2026-03-05 - Last updated in NVD database
Technical Details for CVE-2026-20015
Vulnerability Analysis
This vulnerability stems from improper memory management in the IKEv2 packet processing functionality of Cisco ASA and FTD firewalls. When the affected device receives and parses IKEv2 packets, memory allocated for processing is not properly released after use.
The network-based attack vector with no authentication required means any attacker with network access to the IKEv2 service can trigger this vulnerability. The scope is changed, meaning the vulnerability can impact resources beyond the vulnerable component itself—specifically affecting services dependent on the firewall's availability.
Root Cause
The root cause is a memory leak (CWE-401) in the IKEv2 packet parsing routine. When IKEv2 packets are processed by the affected Cisco ASA or FTD software, the memory allocated during packet parsing is not properly deallocated after the operation completes. Over time, repeated exploitation causes progressive memory exhaustion.
Attack Vector
The attack is conducted remotely over the network against the IKEv2 service, which typically runs on UDP port 500 and UDP port 4500. An attacker can exploit this vulnerability by sending specially crafted IKEv2 packets to an affected device. No authentication is required, and the attacker does not need valid VPN credentials or prior access to the device.
The attack works by continuously sending malformed or crafted IKEv2 packets that trigger the memory leak condition. Each packet causes a small amount of memory to be allocated but never freed. As the attack progresses, available memory on the device decreases until critical system functions are impacted, ultimately causing a denial of service condition that requires manual intervention to resolve.
For detailed technical information about the exploitation mechanism, refer to the Cisco Security Advisory.
Detection Methods for CVE-2026-20015
Indicators of Compromise
- Unexplained gradual memory consumption increase on ASA/FTD devices
- High volume of IKEv2 traffic from single or multiple source IPs
- Firewall instability or unresponsiveness without corresponding configuration changes
- VPN service degradation or failures reported by users
Detection Strategies
- Monitor device memory utilization metrics and alert on sustained increases without corresponding legitimate traffic growth
- Implement IKEv2 traffic analysis to identify abnormal packet patterns or rates
- Configure SNMP traps for memory threshold alerts on ASA/FTD devices
- Review system logs for IKEv2-related errors or unusual parsing events
Monitoring Recommendations
- Establish baseline memory utilization patterns during normal operations for comparison
- Deploy network flow analysis to track IKEv2 traffic volumes and source patterns
- Implement real-time alerting when memory utilization exceeds defined thresholds
- Schedule regular device health checks to proactively identify resource exhaustion trends
How to Mitigate CVE-2026-20015
Immediate Actions Required
- Review the Cisco Security Advisory for specific patch information
- Identify all ASA and FTD devices in your environment with IKEv2 enabled
- Apply vendor patches as soon as they become available
- Implement rate limiting on IKEv2 traffic as an interim mitigation measure
Patch Information
Cisco has published a security advisory detailing affected software versions and available patches. Organizations should consult the Cisco Security Advisory for specific version information and upgrade paths.
Administrators should prioritize patching devices that are directly exposed to untrusted networks or the internet, as these face the highest risk of exploitation.
Workarounds
- If IKEv2 is not required, consider disabling the feature or using IKEv1 as a temporary alternative
- Implement access control lists (ACLs) to restrict IKEv2 traffic to known, trusted IP addresses only
- Configure rate limiting for incoming IKEv2 packets to slow potential exploitation attempts
- Schedule regular device reboots during maintenance windows if patching cannot be immediately performed
# Example: Configure rate limiting for IKEv2 on Cisco ASA (consult documentation for your version)
# Access the ASA command line interface
# Implement connection rate limits for UDP ports 500 and 4500
access-list RATE-LIMIT permit udp any any eq isakmp
access-list RATE-LIMIT permit udp any any eq 4500
class-map IKEv2-TRAFFIC
match access-list RATE-LIMIT
policy-map RATE-LIMIT-POLICY
class IKEv2-TRAFFIC
police input 1000000 1500
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
