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Advisory severityHigh8.6Cisco

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

This high-severity Cisco advisory covers CVE-2026-20301 affecting IOS XE Software.

Aggregated and source-linked by VulniPulse. Data sources, validation and limitations.

cisco-sa-ios-xmcp-thbAr34t Source published Source updated

VulniPulse record published Record updated

CVE-2026-20301
Affected products & platforms
CiscoIOS XE
Open source advisory

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Summary

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.

Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.

There is a mitigation that addresses this vulnerability.

Affected versions
  • Scope: This vulnerability affects Cisco devices if they are running a vulnerable release of Cisco IOS Software or IOS XE Software and have the XMCP Server feature enabled.

Official advisory · high-confidence parse· fetched 24 days ago·verify at source

Fixed versions

No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.

Official advisory · high-confidence parse· fetched 24 days ago·verify at source

Mitigation checklist

Temporary workarounds
  • There are no workarounds that address this vulnerability. However, as a mitigation, administrators may configure an access control allow list to allow only clients that match the specified access list to connect. All other clients will be denied. In the following example configuration, only host 192.168.1.1 is allowed to connect.
  • service-routing xmcp listen
  • allow-list ipv4 XMCPClientListIPv4
  • client username test_xmcp password
  • !
  • ip access-list extended XMCPClientListIPv4
  • permit tcp host 192.168.1.1 any

Official advisory · high-confidence parse· fetched 24 days ago·verify at source

Discussion(0)

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