CVE-2021-1620: Cisco IOS

High severity, CVSS 7.7. EPSS: 1.1% chance of exploitation in the next 30 days.

A vulnerability in the Internet Key Exchange Version 2 (IKEv2) support for the AutoReconnect feature of Cisco IOS Software and Cisco IOS XE Software could allow an authenticated, remote attacker to exhaust the free IP addresses from the assigned local pool. This vulnerability occurs because the code does not release the allocated IP address under certain failure conditions. An attacker could exploit this vulnerability by trying to connect to the device with a non-AnyConnect client. A successful exploit could allow the attacker to exhaust the IP addresses from the assigned local pool, which prevents users from logging in and leads to a denial of service (DoS) condition.

Affected products

• Cisco IOS: version 12.2(6)i1 only; version 15.1(3)svr1 only; version 15.1(3)svr2 only; version 15.1(3)svr3 only; version 15.1(3)svs only; version 15.1(3)svs1 only; …
• Cisco IOS XE: version 3.8.0e only; version 3.8.1e only; version 3.8.2e only; version 3.8.3e only; version 3.8.4e only; version 3.8.5ae only; …

Published 2021-09-23. Last modified 2026-06-17.