Introduction
Critical network infrastructure can be rendered unavailable by a single malformed packet. The recent disclosure of CVE-2025-20253 demonstrates how a flaw in Cisco's IKEv2 implementation can allow unauthenticated remote attackers to force device reloads, resulting in denial of service for enterprise and service provider networks.
Cisco is a global leader in networking and security appliances, with IOS, IOS XE, ASA, and FTD software powering a vast portion of the world's business and service provider networks. The security and reliability of these products are essential for global connectivity and business operations.
Technical Information
CVE-2025-20253 is caused by improper processing of IKEv2 packets in Cisco IOS Software, IOS XE Software, Secure Firewall ASA Software, and Secure FTD Software. The vulnerability is due to insufficient input validation during the parsing of IKEv2 packets. An unauthenticated remote attacker can send specially crafted IKEv2 packets to a vulnerable device. When processed, these packets cause the IKEv2 process to enter an infinite loop, exhausting system resources and forcing the device to reload. This results in a denial of service condition.
The vulnerability is classified as CWE-835 (Loop with Unreachable Exit Condition). Attackers do not need to be authenticated and can exploit the issue remotely by targeting UDP ports 500 and 4500, which are standard for IKEv2 traffic. There are no public code snippets or detailed protocol structures disclosed for this vulnerability.
Affected Systems and Versions
- Cisco IOS Software (exact affected versions not specified in public advisory)
- Cisco IOS XE Software (exact affected versions not specified)
- Cisco Secure Firewall ASA Software (exact affected versions not specified)
- Cisco Secure Firewall Threat Defense (FTD) Software (exact affected versions not specified)
All configurations with IKEv2 enabled and exposed to untrusted networks are potentially vulnerable. The vulnerability affects devices processing IKEv2 packets on UDP ports 500 and 4500.
Vendor Security History
Cisco has a history of IKEv2 and protocol parsing vulnerabilities. Notably, CVE-2025-20182 (disclosed May 2025) affected similar product lines and allowed unauthenticated remote denial of service via crafted IKEv2 messages. CVE-2023-20109 also targeted IKEv2 in Cisco products. Cisco typically responds promptly to vulnerabilities with bundled advisories and coordinated patch releases, but the recurrence of protocol parsing flaws highlights persistent challenges in securing complex network software.