CVE-2025-20182: Cisco ASA Software IKEv2 DoS Vulnerability

CVE-2025-20182 Overview

A denial of service vulnerability exists in the Internet Key Exchange version 2 (IKEv2) protocol processing of Cisco Adaptive Security Appliance (ASA) Software, Cisco Firepower Threat Defense (FTD) Software, Cisco IOS Software, and Cisco IOS XE Software. This vulnerability allows an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device by sending specially crafted IKEv2 traffic.

The vulnerability stems from insufficient input validation when processing IKEv2 messages. A successful exploit could allow the attacker to cause the device to reload, resulting in a complete denial of service condition that disrupts VPN connectivity and network security services.

Critical Impact

Unauthenticated remote attackers can cause Cisco ASA, FTD, IOS, and IOS XE devices to reload by sending crafted IKEv2 traffic, disrupting VPN services and network security operations.

Affected Products

• Cisco Adaptive Security Appliance (ASA) Software versions 9.8.x through 9.20.x
• Cisco Firepower Threat Defense (FTD) Software versions 6.2.3 through 7.4.x
• Cisco IOS Software and Cisco IOS XE Software (with IKEv2 enabled)

Discovery Timeline

• May 7, 2025 - CVE-2025-20182 published to NVD
• August 1, 2025 - Last updated in NVD database

Technical Details for CVE-2025-20182

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-Bounds Write), indicating that the IKEv2 message processing code writes data beyond the boundaries of allocated memory buffers. The flaw is remotely exploitable over the network without requiring authentication or user interaction. An attacker can trigger the vulnerability from any network location that can reach the IKEv2 service (UDP port 500/4500), and the impact extends beyond the vulnerable component to affect the entire device's availability.

The vulnerability affects critical network security infrastructure that organizations rely on for VPN connectivity and secure communications. Given that these devices often sit at network perimeters, successful exploitation could disrupt remote access capabilities and site-to-site VPN tunnels.

Root Cause

The root cause of CVE-2025-20182 is insufficient input validation in the IKEv2 protocol message processing logic. When the affected Cisco software receives specially crafted IKEv2 messages, the parsing routines fail to properly validate message boundaries and field lengths before processing. This leads to an out-of-bounds write condition (CWE-787) where data is written outside the intended memory buffer boundaries.

The lack of proper bounds checking during IKEv2 message handling allows malformed packets to corrupt memory structures, ultimately causing the device to crash and reload. Since IKEv2 is used for establishing IPsec VPN tunnels, the vulnerable code path is exposed whenever the device is configured to handle VPN connections.

Attack Vector

The attack vector for CVE-2025-20182 involves sending crafted IKEv2 protocol messages to an affected device. The attack characteristics include:

• Network-based exploitation: Attackers can target vulnerable devices remotely over UDP ports 500 and 4500 (IKE/NAT-T)
• No authentication required: The vulnerability can be exploited without valid credentials or an established session
• No user interaction needed: The attack is fully automated and does not require any action from users or administrators
• Immediate impact: Successful exploitation causes the device to reload, resulting in service disruption

The attack would typically involve crafting malformed IKEv2 packets with unexpected values in message headers or payloads that trigger the out-of-bounds write condition during parsing. Since IKEv2 is commonly exposed on internet-facing interfaces for remote access VPN functionality, the attack surface can be significant for organizations using these devices.

Detection Methods for CVE-2025-20182

Indicators of Compromise

• Unexpected device reloads or crashes with crashinfo files referencing IKEv2 processing functions
• Syslog messages indicating memory corruption or segmentation faults in IKEv2 handling routines
• Repeated VPN tunnel failures or instability without apparent configuration changes
• Anomalous IKEv2 traffic patterns from unexpected source IP addresses

Detection Strategies

• Monitor device syslog for crash events and correlate with incoming IKEv2 traffic patterns
• Implement network-based intrusion detection rules to identify malformed IKEv2 packets
• Deploy traffic analysis to detect unusual IKEv2 message structures or abnormal packet sizes
• Configure SNMP monitoring to alert on device reloads and availability changes

Monitoring Recommendations

• Enable detailed logging for IKEv2 events on affected Cisco devices
• Implement real-time syslog analysis with alerting for device crash indicators
• Monitor VPN tunnel uptime metrics for sudden drops that may indicate exploitation attempts
• Track IKEv2 connection attempts from unusual geographic locations or IP ranges

How to Mitigate CVE-2025-20182

Immediate Actions Required

• Review the Cisco Security Advisory for specific version guidance and fixed releases
• Inventory all Cisco ASA, FTD, IOS, and IOS XE devices running IKEv2 services
• Prioritize patching for internet-facing devices with IKEv2 exposed to untrusted networks
• Implement access control lists to restrict IKEv2 access to known, trusted IP addresses where possible

Patch Information

Cisco has released fixed software versions to address this vulnerability. Administrators should consult the Cisco Security Advisory for the specific fixed release trains applicable to their deployed versions.

For Cisco ASA Software, fixed versions are available across the 9.x release trains. For Cisco FTD Software, fixes are available in updated versions across the 6.x and 7.x release trains. Organizations should use the Cisco Software Checker tool to identify the appropriate upgrade path for their specific deployment.

Workarounds

• Implement access control lists (ACLs) to limit IKEv2 access to trusted source IP addresses only
• Consider using Control Plane Policing (CoPP) to rate-limit IKEv2 traffic to the device
• If IKEv2 is not required, consider using IKEv1 as a temporary alternative (verify no other vulnerabilities apply)
• Deploy network-based filtering upstream to block malformed IKEv2 packets before they reach vulnerable devices

# Example ACL to restrict IKEv2 access on Cisco ASA (adjust for your environment)
access-list outside_access_in extended permit udp host <trusted_ip> any eq isakmp
access-list outside_access_in extended permit udp host <trusted_ip> any eq 4500
access-list outside_access_in extended deny udp any any eq isakmp
access-list outside_access_in extended deny udp any any eq 4500