CVE-2026-20301 Cisco IOS Software and IOS XE Software Extensible Messaging Client Protocol Denial of Service Vulnerability

High 8.6 Published 5 Aug 2026 Updated 5 Aug 2026

Unauthenticated remote attackers can cause a denial of service by sending malformed XMCP packets to Cisco IOS devices.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: None listed

What is CVE-2026-20301?

CVE-2026-20301 is a high-severity denial of service vulnerability in Cisco Ios, published on 5 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

A vulnerability in the Extensible Messaging Client Protocol (XMCP), also referred to as the External Client protocol, of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to improper handling of malformed XMCP packets. An attacker could exploit this vulnerability by sending a malformed XMCP packet to an affected device. A successful exploit could allow the attacker to cause the affected device to reload unexpectedly, resulting in a DoS condition. The attacker does not need the XMCP client username to exploit this vulnerability.

Weakness: CWE-606

Which versions are affected by CVE-2026-20301?

It affects 2 products.

Products include Cisco Ios, Cisco Ios Xe.

How do I fix CVE-2026-20301?

No fix has been published for CVE-2026-20301 yet. Limit exposure of the affected software until one is available.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-20301 being exploited?

There is no known exploitation of CVE-2026-20301 in the wild and no public exploit code.

All Cisco Ios vulnerabilities

Sources

Also known as GHSA-vfv8-7h88-hj2w.