CVE-2025-20222 Overview
A vulnerability exists in the RADIUS proxy feature for the IPsec VPN feature of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software. This vulnerability allows an unauthenticated, remote attacker to cause a denial of service (DoS) condition by exploiting improper processing of IPv6 packets sent over an IPsec VPN connection.
Critical Impact
Successful exploitation allows remote attackers to trigger a device reload, causing service disruption to all VPN connections and protected network traffic without requiring authentication.
Affected Products
- Cisco Secure Firewall Adaptive Security Appliance (ASA) Software
- Cisco Secure Firewall Threat Defense (FTD) Software
- Systems with RADIUS proxy feature enabled for IPsec VPN
Discovery Timeline
- 2025-08-14 - CVE-2025-20222 published to NVD
- 2025-08-15 - Last updated in NVD database
Technical Details for CVE-2025-20222
Vulnerability Analysis
This vulnerability stems from improper processing of IPv6 packets within the RADIUS proxy feature when used in conjunction with IPsec VPN functionality. When malformed or specially crafted IPv6 packets are transmitted over an established IPsec VPN connection to an affected device, the packet processing logic fails to properly handle these packets, leading to a system crash and subsequent device reload.
The vulnerability is classified under CWE-120 (Buffer Copy without Checking Size of Input), indicating that the root cause involves inadequate bounds checking when processing IPv6 packet data in the RADIUS proxy context. This allows attackers to overflow memory buffers, corrupting critical system state and triggering a device reload.
Root Cause
The vulnerability is caused by insufficient input validation and improper bounds checking when processing IPv6 packets through the RADIUS proxy feature. Specifically, the RADIUS proxy code path does not adequately validate the size of incoming IPv6 packet data before copying it to internal buffers, allowing attackers to exceed expected buffer boundaries and corrupt adjacent memory.
Attack Vector
The attack can be executed remotely over the network without requiring authentication. An attacker must have access to send IPv6 packets through an established IPsec VPN connection to the target device. The attack flow involves:
- Establishing or utilizing an existing IPsec VPN connection to the target Cisco ASA or FTD device
- Sending specially crafted IPv6 packets through the VPN tunnel
- The RADIUS proxy feature improperly processes these packets
- Buffer overflow occurs during packet processing
- Device crashes and reloads, causing denial of service to all connected users
The vulnerability requires the RADIUS proxy feature to be enabled for IPsec VPN, and IPv6 traffic must be permitted through the VPN tunnel. No user interaction is required, and the attack can be automated for persistent denial of service.
Detection Methods for CVE-2025-20222
Indicators of Compromise
- Unexpected device reloads or crashes on Cisco ASA/FTD appliances
- Crash dumps indicating memory corruption in RADIUS proxy or IPsec processing code paths
- Abnormal IPv6 traffic patterns over IPsec VPN connections
- Repeated authentication service disruptions coinciding with high IPv6 VPN traffic
Detection Strategies
- Monitor syslog messages for unexpected reload events with crash codes related to memory corruption
- Implement network traffic analysis to detect anomalous IPv6 packet sizes or malformed headers over VPN tunnels
- Configure SNMP traps for device reload events and correlate with VPN traffic logs
- Enable crash dump collection and analysis to identify exploitation attempts
Monitoring Recommendations
- Deploy SentinelOne Singularity to monitor network edge devices and detect anomalous behavior patterns
- Configure alerting for device availability monitoring with rapid notification on unexpected outages
- Implement baseline tracking for IPv6 traffic volumes over IPsec VPN connections
- Enable detailed logging for RADIUS proxy authentication events and correlate with device stability metrics
How to Mitigate CVE-2025-20222
Immediate Actions Required
- Review the Cisco Security Advisory for affected version details and available patches
- Evaluate whether the RADIUS proxy feature for IPsec VPN can be temporarily disabled until patching is complete
- Implement network access controls to restrict IPv6 traffic over VPN connections where not required
- Plan maintenance windows for applying security updates to affected Cisco ASA and FTD devices
Patch Information
Cisco has released security updates to address this vulnerability. Organizations should consult the Cisco Security Advisory for specific version information and upgrade guidance. Priority should be given to devices exposed to untrusted networks or those providing critical VPN services.
Workarounds
- Disable the RADIUS proxy feature for IPsec VPN if not operationally required
- Implement IPv6 traffic filtering on VPN tunnels to block unauthorized or unnecessary IPv6 packets
- Deploy redundant firewall pairs to maintain availability during potential exploitation attempts
- Consider restricting IPsec VPN access to trusted network segments while awaiting patch deployment
# Example: Check current RADIUS proxy configuration on Cisco ASA
show running-config | include radius-server
show running-config tunnel-group
show vpn-sessiondb detail ra-ikev2-ipsec
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
