Denial of service in Cisco IOS and IOS XE Software

Published: 2021-09-23
Risk Medium
Patch available YES
Number of vulnerabilities 1
CVE-ID CVE-2021-1620
Exploitation vector Network
Public exploit N/A
Vulnerable software
Cisco IOS
Operating systems & Components / Operating system

Cisco IOS XE
Operating systems & Components / Operating system

Vendor Cisco Systems, Inc

Security Bulletin

This security bulletin contains one medium risk vulnerability.

1) Input validation error

EUVDB-ID: #VU56842

Risk: Medium

CVSSv3.1: 6.7 [CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H/E:U/RL:O/RC:C]

CVE-ID: CVE-2021-1620

CWE-ID: CWE-20 - Improper Input Validation

Exploit availability: No


The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.

The vulnerability exists due to the code does not release the allocated IP address under certain failure conditions in the Internet Key Exchange Version 2 (IKEv2) support for the AutoReconnect feature. A remote authenticated attacker can try to connect to the device with a non-AnyConnect client and perform a denial of service (DoS) attack.


Install updates from vendor's website.

Vulnerable software versions

Cisco IOS: 16.9.6, 17.3.1a

Cisco IOS XE: 16.9.6, 17.3.1a

CPE2.3 External links

Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote authenticated user via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.