---
id: CVE-2026-20301
title: >-
  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 se…
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 se…
severity: high
cvss: 8.6
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H'
cwe:
  - CWE-606
vendor: cisco
product: ios
affected:
  - ios = 15.2(1)sy6
  - ios = 15.2(1)sy7
  - ios = 15.2(1)sy8
  - ios = 15.2(2)e8
  - ios = 15.2(2)e9
  - ios = 15.2(2)e9a
  - ios = 15.2(2)e10
  - ios = 15.2(2)e10a
  - ios = 15.2(2)e10b
  - ios = 15.2(2)e10c
  - ios = 15.2(4)e6
  - ios = 15.2(4)e7
  - ios = 15.2(4)e8
  - ios = 15.2(4)e9
  - ios = 15.2(4)e10
  - ios = 15.2(4)e10a
  - ios = 15.2(4)e10b
  - ios = 15.2(4)e10c
  - ios = 15.2(4)e10d
  - ios = 15.2(4)e10e
  - ios = 15.2(4)ea7
  - ios = 15.2(4)ea8
  - ios = 15.2(4)ea9
  - ios = 15.2(4)ea9a
  - ios = 15.2(6)e1
  - ios = 15.2(6)e1a
  - ios = 15.2(6)e1s
  - ios = 15.2(6)e2
  - ios = 15.2(6)e2a
  - ios = 15.2(6)e2b
  - ios = 15.2(6)e3
  - ios = 15.2(7)e
  - ios = 15.2(7)e0a
  - ios = 15.2(7)e0b
  - ios = 15.2(7)e0s
  - ios = 15.2(7)e1
  - ios = 15.2(7)e1a
  - ios = 15.2(7)e2
  - ios = 15.2(7)e2b
  - ios = 15.2(7)e3
  - ios = 15.2(7)e3k
  - ios = 15.2(7)e4
  - ios = 15.2(7)e5
  - ios = 15.2(7)e6
  - ios = 15.2(7)e7
  - ios = 15.2(7)e8
  - ios = 15.2(7)e9
  - ios = 15.2(7)e10
  - ios = 15.2(7)e11
  - ios = 15.2(7)e12
  - ios = 15.2(7)e13
  - ios = 15.2(7)e14
  - ios = 15.2(8)e
  - ios = 15.2(8)e1
  - ios = 15.2(8)e2
  - ios = 15.2(8)e3
  - ios = 15.2(8)e4
  - ios = 15.2(8)e5
  - ios = 15.2(8)e6
  - ios = 15.2(8)e7
  - ios = 15.2(8)e8
  - ios = 15.4(1)sy4
  - ios = 15.5(1)sy1
  - ios = 15.5(1)sy2
  - ios = 15.5(1)sy3
  - ios = 15.5(1)sy4
  - ios = 15.5(1)sy5
  - ios = 15.5(1)sy6
  - ios = 15.5(1)sy7
  - ios = 15.5(1)sy8
  - ios = 15.5(1)sy9
  - ios = 15.5(1)sy10
  - ios = 15.5(1)sy11
  - ios = 15.5(1)sy12
  - ios = 15.5(1)sy13
  - ios = 15.5(1)sy14
  - ios = 15.5(1)sy15
  - ios = 15.5(1)sy16
  - ios = 15.5(1)sy17
  - ios = 15.6(2)sp4
  - ios = 15.6(2)sp5
  - ios = 15.6(2)sp6
  - ios = 15.6(2)sp7
  - ios = 15.6(2)sp8
  - ios = 15.6(2)sp8a
  - ios = 15.6(2)sp9
  - ios = 15.7(3)m2
  - ios = 15.7(3)m3
  - ios = 15.7(3)m4
  - ios = 15.7(3)m4a
  - ios = 15.7(3)m4b
  - ios = 15.7(3)m5
  - ios = 15.7(3)m6
  - ios = 15.7(3)m7
  - ios = 15.7(3)m8
  - ios = 15.7(3)m9
  - ios = 15.7(3)m10
  - ios = 15.7(3)m10a
  - ios = 15.7(3)m10b
  - ios = 15.8(3)m
published: '2026-08-05'
updated: '2026-09-17'
sourceUpdated: '2026-09-17T18:05:21.583'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-20301'
references:
  - url: >-
      https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ios-xmcp-thbAr34t
    label: psirt@cisco.com
tags:
  - nvd
epss: 0.00573
epssPercentile: 0.44961
ingestedAt: '2026-09-17T18:25:15.982Z'
---

## Overview

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.

## Affected

- `ios = 15.2(1)sy6`
- `ios = 15.2(1)sy7`
- `ios = 15.2(1)sy8`
- `ios = 15.2(2)e8`
- `ios = 15.2(2)e9`
- `ios = 15.2(2)e9a`
- `ios = 15.2(2)e10`
- `ios = 15.2(2)e10a`
- `ios = 15.2(2)e10b`
- `ios = 15.2(2)e10c`
- `ios = 15.2(4)e6`
- `ios = 15.2(4)e7`
- `ios = 15.2(4)e8`
- `ios = 15.2(4)e9`
- `ios = 15.2(4)e10`
- `ios = 15.2(4)e10a`
- `ios = 15.2(4)e10b`
- `ios = 15.2(4)e10c`
- `ios = 15.2(4)e10d`
- `ios = 15.2(4)e10e`
- `ios = 15.2(4)ea7`
- `ios = 15.2(4)ea8`
- `ios = 15.2(4)ea9`
- `ios = 15.2(4)ea9a`
- `ios = 15.2(6)e1`
- `ios = 15.2(6)e1a`
- `ios = 15.2(6)e1s`
- `ios = 15.2(6)e2`
- `ios = 15.2(6)e2a`
- `ios = 15.2(6)e2b`
- `ios = 15.2(6)e3`
- `ios = 15.2(7)e`
- `ios = 15.2(7)e0a`
- `ios = 15.2(7)e0b`
- `ios = 15.2(7)e0s`
- `ios = 15.2(7)e1`
- `ios = 15.2(7)e1a`
- `ios = 15.2(7)e2`
- `ios = 15.2(7)e2b`
- `ios = 15.2(7)e3`
- `ios = 15.2(7)e3k`
- `ios = 15.2(7)e4`
- `ios = 15.2(7)e5`
- `ios = 15.2(7)e6`
- `ios = 15.2(7)e7`
- `ios = 15.2(7)e8`
- `ios = 15.2(7)e9`
- `ios = 15.2(7)e10`
- `ios = 15.2(7)e11`
- `ios = 15.2(7)e12`
- `ios = 15.2(7)e13`
- `ios = 15.2(7)e14`
- `ios = 15.2(8)e`
- `ios = 15.2(8)e1`
- `ios = 15.2(8)e2`
- `ios = 15.2(8)e3`
- `ios = 15.2(8)e4`
- `ios = 15.2(8)e5`
- `ios = 15.2(8)e6`
- `ios = 15.2(8)e7`
- `ios = 15.2(8)e8`
- `ios = 15.4(1)sy4`
- `ios = 15.5(1)sy1`
- `ios = 15.5(1)sy2`
- `ios = 15.5(1)sy3`
- `ios = 15.5(1)sy4`
- `ios = 15.5(1)sy5`
- `ios = 15.5(1)sy6`
- `ios = 15.5(1)sy7`
- `ios = 15.5(1)sy8`
- `ios = 15.5(1)sy9`
- `ios = 15.5(1)sy10`
- `ios = 15.5(1)sy11`
- `ios = 15.5(1)sy12`
- `ios = 15.5(1)sy13`
- `ios = 15.5(1)sy14`
- `ios = 15.5(1)sy15`
- `ios = 15.5(1)sy16`
- `ios = 15.5(1)sy17`
- `ios = 15.6(2)sp4`
- `ios = 15.6(2)sp5`
- `ios = 15.6(2)sp6`
- `ios = 15.6(2)sp7`
- `ios = 15.6(2)sp8`
- `ios = 15.6(2)sp8a`
- `ios = 15.6(2)sp9`
- `ios = 15.7(3)m2`
- `ios = 15.7(3)m3`
- `ios = 15.7(3)m4`
- `ios = 15.7(3)m4a`
- `ios = 15.7(3)m4b`
- `ios = 15.7(3)m5`
- `ios = 15.7(3)m6`
- `ios = 15.7(3)m7`
- `ios = 15.7(3)m8`
- `ios = 15.7(3)m9`
- `ios = 15.7(3)m10`
- `ios = 15.7(3)m10a`
- `ios = 15.7(3)m10b`
- `ios = 15.8(3)m`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.