CVE-2026-20301
Cisco IOS Software and IOS XE Software Extensible Messaging Client Protocol Denial of Service Vulnerability
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
Affected products
| Vendor | Product | Category | Matched by |
|---|---|---|---|
| Cisco | Cisco IOS Software | Routing & Switching | cna-assigner |
| Cisco | Cisco IOS XE Software | Routing & Switching | cna-assigner |
Vendor-reported products (2)
- Cisco · Cisco IOS XE Software
- Cisco · IOS
Vendor advisory
Cisco IOS Software and IOS XE Software Extensible Messaging Client Protocol Denial of Service Vulnerability
Cisco’s rating: High (advisory CVSS 8.6) · Published Aug 5, 2026
Bug ID: CSCwu20827
The vendor’s rating applies to the whole advisory and can differ from this CVE’s own CVSS severity. Where this comes from