CVE-2021-1620 : What You Need to Know

A vulnerability in the Internet Key Exchange Version 2 (IKEv2) support for the AutoReconnect feature of Cisco IOS Software and Cisco IOS XE Software has been identified. This could allow an authenticated, remote attacker to exhaust free IP addresses from the assigned local pool, leading to a denial of service (DoS) condition.

Understanding CVE-2021-1620

This CVE-2021-1620 advisory was published on September 22, 2021, with a high base severity score of 7.7. The vulnerability affects Cisco IOS and IOS XE Software, potentially impacting network availability.

What is CVE-2021-1620?

The vulnerability lies in the IKEv2 support for the AutoReconnect feature, permitting an attacker to deplete IP addresses from the local pool by exploiting certain failure conditions in the code. Successful exploitation could result in users being unable to log in, causing a DoS situation.

The Impact of CVE-2021-1620

If exploited, the vulnerability can lead to a denial of service condition, preventing legitimate users from accessing the network services due to the exhaustion of available IP addresses.

Technical Details of CVE-2021-1620

The CVSS V3.1 base score for CVE-2021-1620 is 7.7, indicating a high severity level with a LOW attack complexity and NETWORK attack vector. The vulnerability has a HIGH impact on availability.

Vulnerability Description

The vulnerability in the IKEv2 support for AutoReconnect can be exploited by an authenticated, remote attacker to exhaust free IP addresses and trigger a DoS condition.

Affected Systems and Versions

The vulnerability affects Cisco IOS Software and Cisco IOS XE Software. All versions are susceptible to the exploitation of the AutoReconnect feature.

Exploitation Mechanism

Attackers can exploit the vulnerability by attempting to connect to the device using a non-AnyConnect client, leading to the depletion of IP addresses from the local pool.

Mitigation and Prevention

To address CVE-2021-1620, immediate steps and long-term security practices are recommended.

Immediate Steps to Take

Users are advised to apply security patches from Cisco to mitigate the vulnerability and prevent potential exploitation. Additionally, network administrators should monitor IP address allocation to detect any unusual patterns that may indicate an ongoing attack.

Long-Term Security Practices

Implementing strong network segmentation, access control policies, and regular security audits can enhance the overall security posture of the network and prevent similar vulnerabilities from being exploited.

Patching and Updates

Regularly check for security advisories from Cisco and promptly apply any recommended patches or updates to ensure that systems are protected from known vulnerabilities.