CVE-2025-20222 is a critical buffer overflow vulnerability affecting the RADIUS proxy feature within the IPsec VPN functionality of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software. This vulnerability arises from improper processing of IPv6 packets, specifically a buffer copy operation that does not verify the size of the input data, leading to a classic buffer overflow condition. An unauthenticated remote attacker can exploit this flaw by sending specially crafted IPv6 packets over an IPsec VPN connection to an affected device. Successful exploitation forces the device to reload unexpectedly, causing a denial of service (DoS) condition. The vulnerability affects a broad range of Cisco Firepower Threat Defense software versions, spanning multiple major and minor releases from 6.2.3 through 7.4.2.1 and 7.2.9, indicating a widespread exposure across many deployed systems. The CVSS v3.1 base score is 8.6, classified as high severity, reflecting the vulnerability's network attack vector, low attack complexity, no required privileges or user interaction, and a significant impact on availability without affecting confidentiality or integrity. Although no known exploits are reported in the wild yet, the ease of exploitation and the critical nature of the impacted devices make this vulnerability a significant risk for organizations relying on Cisco ASA and FTD devices for secure VPN connectivity and perimeter defense. The vulnerability could disrupt business operations by causing unexpected device reboots and loss of VPN connectivity, potentially impacting remote access and inter-site communications.

For European organizations, this vulnerability poses a substantial risk to network security infrastructure, particularly for enterprises, government agencies, and critical infrastructure operators that utilize Cisco ASA and FTD devices for VPN and firewall services. The denial of service condition could lead to temporary loss of secure remote access, interruption of critical business processes, and potential exposure to secondary attacks during downtime. Given the widespread deployment of Cisco security appliances in Europe, especially in sectors such as finance, telecommunications, healthcare, and public administration, the impact could be severe. Disruptions in VPN connectivity may hinder remote workforce productivity and secure communications between branch offices. Additionally, the vulnerability could be leveraged as part of a larger attack campaign to degrade network defenses or create diversionary conditions for other malicious activities. The lack of required authentication lowers the barrier for attackers, increasing the likelihood of exploitation attempts. Organizations with IPv6-enabled IPsec VPN deployments are particularly at risk, as the vulnerability specifically targets IPv6 packet processing.

To mitigate this vulnerability effectively, European organizations should prioritize the following actions: 1) Immediate identification and inventory of all Cisco ASA and FTD devices running affected software versions, with special attention to those configured with IPsec VPN and RADIUS proxy features. 2) Apply Cisco's official patches or software updates as soon as they become available, ensuring that devices are upgraded to versions that address the buffer overflow issue. 3) In the interim, consider disabling IPv6 support on IPsec VPN interfaces if IPv6 is not required, to reduce the attack surface. 4) Implement network-level filtering to restrict or monitor IPv6 traffic entering VPN endpoints, using intrusion detection/prevention systems to detect anomalous packet patterns. 5) Enhance logging and monitoring for unusual device reloads or VPN disruptions that may indicate exploitation attempts. 6) Conduct regular vulnerability assessments and penetration testing focused on VPN infrastructure to identify and remediate potential weaknesses. 7) Develop and test incident response plans specifically for network device DoS scenarios to minimize operational impact. These measures go beyond generic advice by focusing on IPv6 traffic controls, device-specific patch management, and proactive detection tailored to the vulnerability's characteristics.