CVE-2021-1620: Cisco IOS and IOS XE Software IKEv2 AutoReconnect Feature Denial of Service Vulnerability

Severity: high (CVSS 7.7 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-09-23 · updated 2026-06-17
Weakness: CWE-563

Description

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: 12.2(6)i1, 15.1(3)svr1, 15.1(3)svr2, 15.1(3)svr3, 15.1(3)svs, 15.1(3)svs1 (+406)
Cisco IOS XE: 3.8.0e, 3.8.1e, 3.8.2e, 3.8.3e, 3.8.4e, 3.8.5ae (+271)

References

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