CVE-2025-20252 Overview
CVE-2025-20252 is a memory leak vulnerability in the Internet Key Exchange Version 2 (IKEv2) module of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Secure Firewall Threat Defense (FTD) Software. An unauthenticated, remote attacker can trigger the flaw by sending a continuous stream of crafted IKEv2 packets to an affected device. Successful exploitation partially exhausts system memory, producing instability such as the inability to establish new IKEv2 VPN sessions. Recovery from the condition requires a manual reboot of the device. The weakness is tracked as [CWE-401] Missing Release of Memory after Effective Lifetime.
Critical Impact
Remote unauthenticated attackers can degrade IKEv2 VPN availability on Cisco ASA and FTD firewalls, requiring a manual reboot to restore service.
Affected Products
- Cisco Secure Firewall Adaptive Security Appliance (ASA) Software
- Cisco Secure Firewall Threat Defense (FTD) Software
- Devices running the IKEv2 module for remote-access or site-to-site VPN
Discovery Timeline
- 2025-08-14 - CVE-2025-20252 published to the National Vulnerability Database
- 2026-06-17 - Last updated in the NVD database
Technical Details for CVE-2025-20252
Vulnerability Analysis
The vulnerability resides in the IKEv2 parsing logic within Cisco ASA and FTD Software. When the device processes malformed IKEv2 packets, memory allocated during parsing is not released after the packet is discarded. Each crafted packet leaks a small amount of memory. Over a sustained stream of packets, the cumulative loss degrades system stability. Because IKEv2 is a stateless UDP-based key exchange protocol, no authentication or established session is required prior to reaching the vulnerable code path. Attackers can therefore exploit the flaw remotely without credentials or user interaction. The impact is limited to availability, and confidentiality and integrity are unaffected.
Root Cause
The root cause is improper parsing of IKEv2 packets that fails to free previously allocated buffers when malformed input triggers an error path. This omission constitutes a classic [CWE-401] memory leak. Repeated invocation of the affected code path drains the pool used by IKEv2 session management. Once the pool contracts sufficiently, new VPN session establishment fails even though the control plane remains partially responsive.
Attack Vector
An attacker sends a continuous stream of crafted IKEv2 packets to UDP port 500 or 4500 on the exposed firewall interface. No authentication, prior session, or user interaction is required. The attack is remotely reachable across the network wherever the IKEv2 service is exposed, which typically includes internet-facing VPN concentrators. Sustained transmission is required to accumulate the leak into a service-affecting condition. Recovery requires operator intervention to reboot the device.
No public proof-of-concept exploit code is available for this issue. Refer to the Cisco Security Advisory for authoritative technical details.
Detection Methods for CVE-2025-20252
Indicators of Compromise
- Steady decline in available system memory reported by show memory or SNMP polling on ASA and FTD devices
- Failures to establish new IKEv2 VPN sessions while existing sessions remain active
- High volumes of malformed or repeated IKEv2 initiator packets arriving on UDP 500 or 4500
- Syslog messages related to IKEv2 packet parsing errors preceding memory pressure alerts
Detection Strategies
- Baseline IKEv2 process memory consumption and alert on sustained downward trends that do not correlate with legitimate session growth
- Inspect NetFlow or firewall logs for a single source or small set of sources generating abnormal IKEv2 traffic rates
- Correlate VPN session establishment failures with concurrent memory utilization anomalies on the same device
Monitoring Recommendations
- Enable SNMP traps for the ASA and FTD memory utilization OIDs and route them to the SIEM for trend analysis
- Forward device syslog to a centralized log platform and build detections for IKEv2 error messages
- Monitor perimeter UDP 500 and 4500 traffic for volumetric anomalies against historical baselines
How to Mitigate CVE-2025-20252
Immediate Actions Required
- Review the Cisco Security Advisory and identify affected ASA and FTD releases in your environment
- Apply the fixed software releases published by Cisco as soon as maintenance windows allow
- Restrict IKEv2 exposure to trusted peer addresses where feasible using control-plane access controls
- Prepare an operational runbook for detecting memory exhaustion and rebooting affected devices to restore service
Patch Information
Cisco has published fixed software versions for both Secure Firewall ASA Software and Secure Firewall Threat Defense Software. Consult the Cisco Security Advisory for the version matrix mapped to your platform and upgrade path. No workaround fully addresses the underlying parsing defect; upgrading is the recommended remediation.
Workarounds
- Apply infrastructure access control lists that permit IKEv2 traffic only from known VPN peer addresses
- Rate-limit UDP 500 and 4500 traffic at upstream routers or edge devices to slow leak accumulation
- Schedule proactive reboots during maintenance windows if memory pressure is observed prior to patching
# Example: restrict IKEv2 to known peers on Cisco ASA
access-list IKEv2-CONTROL extended permit udp host <peer-ip> any eq isakmp
access-list IKEv2-CONTROL extended permit udp host <peer-ip> any eq 4500
access-list IKEv2-CONTROL extended deny udp any any eq isakmp
access-list IKEv2-CONTROL extended deny udp any any eq 4500
control-plane
service-policy input IKEv2-CONTROL
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
