CVE-2026-20301: Cisco IOS Software and IOS XE Software Extensible Messaging Client Protocol Denial of Service Vulnerability
Published Aug 5, 2026
·Updated
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 Software
430 affected components
Cisco IOS Software
Cisco IOS XE Software
Cisco Extensible Messaging Client Protocol (XMCP)
Cisco IOS=15.2\(1\)sy6
Cisco IOS=15.2\(1\)sy7
Cisco IOS=15.2\(1\)sy8
Cisco IOS=15.2\(2\)e8
Cisco IOS=15.2\(2\)e9
Cisco IOS=15.2\(2\)e9a
Cisco IOS=15.2\(2\)e10
Cisco IOS=15.2\(2\)e10a
Cisco IOS=15.2\(2\)e10b
Cisco IOS=15.2\(2\)e10c
Cisco IOS=15.2\(4\)e6
Cisco IOS=15.2\(4\)e7
Cisco IOS=15.2\(4\)e8
Cisco IOS=15.2\(4\)e9
Cisco IOS=15.2\(4\)e10
Cisco IOS=15.2\(4\)e10a
Cisco IOS=15.2\(4\)e10b
Cisco IOS=15.2\(4\)e10c
Cisco IOS=15.2\(4\)e10d
Cisco IOS=15.2\(4\)e10e
Cisco IOS=15.2\(4\)ea7
Cisco IOS=15.2\(4\)ea8
Cisco IOS=15.2\(4\)ea9
Cisco IOS=15.2\(4\)ea9a
Cisco IOS=15.2\(6\)e1
Cisco IOS=15.2\(6\)e1a
Cisco IOS=15.2\(6\)e1s
Cisco IOS=15.2\(6\)e2
Cisco IOS=15.2\(6\)e2a
Cisco IOS=15.2\(6\)e2b
Cisco IOS=15.2\(6\)e3
Cisco IOS=15.2\(7\)e
Cisco IOS=15.2\(7\)e0a
Cisco IOS=15.2\(7\)e0b
Cisco IOS=15.2\(7\)e0s
Cisco IOS=15.2\(7\)e1
Cisco IOS=15.2\(7\)e1a
Cisco IOS=15.2\(7\)e2
Cisco IOS=15.2\(7\)e2b
Cisco IOS=15.2\(7\)e3
Cisco IOS=15.2\(7\)e3k
Cisco IOS=15.2\(7\)e4
Cisco IOS=15.2\(7\)e5
Cisco IOS=15.2\(7\)e6
Cisco IOS=15.2\(7\)e7
Cisco IOS=15.2\(7\)e8
Cisco IOS=15.2\(7\)e9
Cisco IOS=15.2\(7\)e10
Cisco IOS=15.2\(7\)e11
Cisco IOS=15.2\(7\)e12
Cisco IOS=15.2(7)e13
Cisco IOS=15.2\(7\)e14
Cisco IOS=15.2\(8\)e
Cisco IOS=15.2\(8\)e1
Cisco IOS=15.2\(8\)e2
Cisco IOS=15.2\(8\)e3
Cisco IOS=15.2\(8\)e4
Cisco IOS=15.2\(8\)e5
Cisco IOS=15.2\(8\)e6
Cisco IOS=15.2\(8\)e7
Cisco IOS=15.2(8)e8
Cisco IOS=15.4\(1\)sy4
Cisco IOS=15.5\(1\)sy1
Cisco IOS=15.5\(1\)sy2
Cisco IOS=15.5\(1\)sy3
Cisco IOS=15.5\(1\)sy4
Cisco IOS=15.5\(1\)sy5
Cisco IOS=15.5\(1\)sy6
Cisco IOS=15.5\(1\)sy7
Cisco IOS=15.5\(1\)sy8
Cisco IOS=15.5\(1\)sy9
Cisco IOS=15.5\(1\)sy10
Cisco IOS=15.5\(1\)sy11
Cisco IOS=15.5\(1\)sy12
Cisco IOS=15.5\(1\)sy13
Cisco IOS=15.5\(1\)sy14
Cisco IOS=15.5\(1\)sy15
Cisco IOS=15.5\(1\)sy16
Cisco IOS=15.5\(1\)sy17
Cisco IOS=15.6\(2\)sp4
Cisco IOS=15.6\(2\)sp5
Cisco IOS=15.6\(2\)sp6
Cisco IOS=15.6\(2\)sp7
Cisco IOS=15.6\(2\)sp8
Cisco IOS=15.6\(2\)sp8a
Cisco IOS=15.6\(2\)sp9
Cisco IOS=15.7\(3\)m2
Cisco IOS=15.7\(3\)m3
Cisco IOS=15.7\(3\)m4
Cisco IOS=15.7\(3\)m4a
Cisco IOS=15.7\(3\)m4b
Cisco IOS=15.7\(3\)m5
Cisco IOS=15.7\(3\)m6
Cisco IOS=15.7\(3\)m7
Cisco IOS=15.7\(3\)m8
Cisco IOS=15.7\(3\)m9
Cisco IOS=15.7\(3\)m10
Cisco IOS=15.7\(3\)m10a
Cisco IOS=15.7\(3\)m10b
Cisco IOS=15.8\(3\)m
Cisco IOS=15.8\(3\)m0a
Cisco IOS=15.8\(3\)m0b
Cisco IOS=15.8\(3\)m1
Cisco IOS=15.8\(3\)m1a
Cisco IOS=15.8\(3\)m2
Cisco IOS=15.8\(3\)m2a
Cisco IOS=15.8\(3\)m3
Cisco IOS=15.8\(3\)m3a
Cisco IOS=15.8\(3\)m3b
Cisco IOS=15.8\(3\)m4
Cisco IOS=15.8\(3\)m5
Cisco IOS=15.8\(3\)m6
Cisco IOS=15.8\(3\)m7
Cisco IOS=15.8\(3\)m8
Cisco IOS=15.8\(3\)m9
Cisco IOS=15.9\(3\)m
Cisco IOS=15.9\(3\)m0a
Cisco IOS=15.9\(3\)m1
Cisco IOS=15.9\(3\)m2
Cisco IOS=15.9\(3\)m2a
Cisco IOS=15.9\(3\)m3
Cisco IOS=15.9\(3\)m3a
Cisco IOS=15.9\(3\)m3b
Cisco IOS=15.9\(3\)m4
Cisco IOS=15.9\(3\)m4a
Cisco IOS=15.9\(3\)m5
Cisco IOS=15.9\(3\)m6
Cisco IOS=15.9\(3\)m6a
Cisco IOS=15.9\(3\)m6b
Cisco IOS=15.9\(3\)m7
Cisco IOS=15.9\(3\)m7a
Cisco IOS=15.9\(3\)m8
Cisco IOS=15.9\(3\)m8a
Cisco IOS=15.9\(3\)m8b
Cisco IOS=15.9\(3\)m9
Cisco IOS=15.9\(3\)m9a
Cisco IOS=15.9\(3\)m10
Cisco IOS=15.9\(3\)m11
Cisco IOS=15.9\(3\)m12
Cisco IOS=15.9\(3\)m13
Cisco IOS XE=3.8.10ce
Cisco IOS XE=3.8.10de
Cisco IOS XE=3.11.3ae
Cisco IOS XE=3.11.3e
Cisco IOS XE=3.11.4e
Cisco IOS XE=3.11.5e
Cisco IOS XE=3.11.6e
Cisco IOS XE=3.11.7e
Cisco IOS XE=3.11.8e
Cisco IOS XE=3.11.9e
Cisco IOS XE=3.11.10e
Cisco IOS XE=3.11.11e
Cisco IOS XE=3.11.12e
Cisco IOS XE=3.11.13e
Cisco IOS XE=3.11.14e
Cisco IOS XE=3.16.10as
Cisco IOS XE=3.16.10bs
Cisco IOS XE=3.18.8asp
Cisco IOS XE=3.18.9sp
Cisco IOS XE=16.6.2
Cisco IOS XE=16.6.3
Cisco IOS XE=16.6.4
Cisco IOS XE=16.6.4a
Cisco IOS XE=16.6.4s
Cisco IOS XE=16.6.5
Cisco IOS XE=16.6.5a
Cisco IOS XE=16.6.5b
Cisco IOS XE=16.6.6
Cisco IOS XE=16.6.7
Cisco IOS XE=16.6.7a
Cisco IOS XE=16.6.8
Cisco IOS XE=16.6.9
Cisco IOS XE=16.6.10
Cisco IOS XE=16.7.1
Cisco IOS XE=16.7.1a
Cisco IOS XE=16.7.1b
Cisco IOS XE=16.7.2
Cisco IOS XE=16.7.3
Cisco IOS XE=16.7.4
Cisco IOS XE=16.8.1
Cisco IOS XE=16.8.1a
Cisco IOS XE=16.8.1b
Cisco IOS XE=16.8.1c
Cisco IOS XE=16.8.1d
Cisco IOS XE=16.8.1e
Cisco IOS XE=16.8.1s
Cisco IOS XE=16.8.2
Cisco IOS XE=16.8.3
Cisco IOS XE=16.9.1
Cisco IOS XE=16.9.1a
Cisco IOS XE=16.9.1b
Cisco IOS XE=16.9.1c
Cisco IOS XE=16.9.1d
Cisco IOS XE=16.9.1s
Cisco IOS XE=16.9.2
Cisco IOS XE=16.9.2a
Cisco IOS XE=16.9.2s
Cisco IOS XE=16.9.3
Cisco IOS XE=16.9.3a
Cisco IOS XE=16.9.3h
Cisco IOS XE=16.9.3s
Cisco IOS XE=16.9.4
Cisco IOS XE=16.9.4c
Cisco IOS XE=16.9.5
Cisco IOS XE=16.9.5f
Cisco IOS XE=16.9.6
Cisco IOS XE=16.9.7
Cisco IOS XE=16.9.8
Cisco IOS XE=16.9.8a
Cisco IOS XE=16.9.8b
Cisco IOS XE=16.10.1
Cisco IOS XE=16.10.1a
Cisco IOS XE=16.10.1b
Cisco IOS XE=16.10.1c
Cisco IOS XE=16.10.1d
Cisco IOS XE=16.10.1e
Cisco IOS XE=16.10.1f
Cisco IOS XE=16.10.1g
Cisco IOS XE=16.10.1s
Cisco IOS XE=16.10.2
Cisco IOS XE=16.10.3
Cisco IOS XE=16.11.1
Cisco IOS XE=16.11.1a
Cisco IOS XE=16.11.1b
Cisco IOS XE=16.11.1c
Cisco IOS XE=16.11.1s
Cisco IOS XE=16.11.2
Cisco IOS XE=16.12.1
Cisco IOS XE=16.12.1a
Cisco IOS XE=16.12.1c
Cisco IOS XE=16.12.1s
Cisco IOS XE=16.12.1t
Cisco IOS XE=16.12.1w
Cisco IOS XE=16.12.1x
Cisco IOS XE=16.12.1y
Cisco IOS XE=16.12.1z
Cisco IOS XE=16.12.1z1
Cisco IOS XE=16.12.1z2
Cisco IOS XE=16.12.2
Cisco IOS XE=16.12.2a
Cisco IOS XE=16.12.2s
Cisco IOS XE=16.12.2t
Cisco IOS XE=16.12.3
Cisco IOS XE=16.12.3a
Cisco IOS XE=16.12.3s
Cisco IOS XE=16.12.4
Cisco IOS XE=16.12.4a
Cisco IOS XE=16.12.5
Cisco IOS XE=16.12.5a
Cisco IOS XE=16.12.5b
Cisco IOS XE=16.12.6
Cisco IOS XE=16.12.6a
Cisco IOS XE=16.12.7
Cisco IOS XE=16.12.8
Cisco IOS XE=16.12.9
Cisco IOS XE=16.12.10
Cisco IOS XE=16.12.10a
Cisco IOS XE=16.12.11
Cisco IOS XE=16.12.12
Cisco IOS XE=16.12.13
Cisco IOS XE=16.12.14
Cisco IOS XE=16.12.15
Cisco IOS XE=16.12.16
Cisco IOS XE=17.1.1
Cisco IOS XE=17.1.1a
Cisco IOS XE=17.1.1s
Cisco IOS XE=17.1.1t
Cisco IOS XE=17.1.2
Cisco IOS XE=17.1.3
Cisco IOS XE=17.2.1
Cisco IOS XE=17.2.1a
Cisco IOS XE=17.2.1r
Cisco IOS XE=17.2.1v
Cisco IOS XE=17.2.2
Cisco IOS XE=17.2.3
Cisco IOS XE=17.3.1
Cisco IOS XE=17.3.1a
Cisco IOS XE=17.3.1w
Cisco IOS XE=17.3.1x
Cisco IOS XE=17.3.1z
Cisco IOS XE=17.3.2
Cisco IOS XE=17.3.2a
Cisco IOS XE=17.3.3
Cisco IOS XE=17.3.3a
Cisco IOS XE=17.3.4
Cisco IOS XE=17.3.4a
Cisco IOS XE=17.3.4b
Cisco IOS XE=17.3.4c
Cisco IOS XE=17.3.5
Cisco IOS XE=17.3.5a
Cisco IOS XE=17.3.5b
Cisco IOS XE=17.3.6
Cisco IOS XE=17.3.7
Cisco IOS XE=17.3.8
Cisco IOS XE=17.3.8a
Cisco IOS XE=17.4.1
Cisco IOS XE=17.4.1a
Cisco IOS XE=17.4.1b
Cisco IOS XE=17.4.1c
Cisco IOS XE=17.4.2
Cisco IOS XE=17.4.2a
Cisco IOS XE=17.5.1
Cisco IOS XE=17.5.1a
Cisco IOS XE=17.6.1
Cisco IOS XE=17.6.1a
Cisco IOS XE=17.6.1x
Cisco IOS XE=17.6.1z
Cisco IOS XE=17.6.1z1
Cisco IOS XE=17.6.2
Cisco IOS XE=17.6.3
Cisco IOS XE=17.6.3a
Cisco IOS XE=17.6.4
Cisco IOS XE=17.6.5
Cisco IOS XE=17.6.5a
Cisco IOS XE=17.6.6
Cisco IOS XE=17.6.6a
Cisco IOS XE=17.6.7
Cisco IOS XE=17.6.8
Cisco IOS XE=17.6.8a
Cisco IOS XE=17.7.1
Cisco IOS XE=17.7.1a
Cisco IOS XE=17.7.1b
Cisco IOS XE=17.7.2
Cisco IOS XE=17.8.1
Cisco IOS XE=17.8.1a
Cisco IOS XE=17.9.1
Cisco IOS XE=17.9.1a
Cisco IOS XE=17.9.1w
Cisco IOS XE=17.9.1x
Cisco IOS XE=17.9.1x1
Cisco IOS XE=17.9.1y
Cisco IOS XE=17.9.1y1
Cisco IOS XE=17.9.2
Cisco IOS XE=17.9.2a
Cisco IOS XE=17.9.3
Cisco IOS XE=17.9.3a
Cisco IOS XE=17.9.4
Cisco IOS XE=17.9.4a
Cisco IOS XE=17.9.5
Cisco IOS XE=17.9.5a
Cisco IOS XE=17.9.5b
Cisco IOS XE=17.9.5c
Cisco IOS XE=17.9.5d
Cisco IOS XE=17.9.5e
Cisco IOS XE=17.9.5f
Cisco IOS XE=17.9.6
Cisco IOS XE=17.9.6a
Cisco IOS XE=17.9.7
Cisco IOS XE=17.9.7a
Cisco IOS XE=17.9.7b
Cisco IOS XE=17.9.8
Cisco IOS XE=17.9.9
Cisco IOS XE=17.10.1
Cisco IOS XE=17.10.1a
Cisco IOS XE=17.10.1b
Cisco IOS XE=17.11.1
Cisco IOS XE=17.11.1a
Cisco IOS XE=17.12.1
Cisco IOS XE=17.12.1a
Cisco IOS XE=17.12.1w
Cisco IOS XE=17.12.1x
Cisco IOS XE=17.12.1y
Cisco IOS XE=17.12.1z
Cisco IOS XE=17.12.1z1
Cisco IOS XE=17.12.1z2
Cisco IOS XE=17.12.1z3
Cisco IOS XE=17.12.1z4
Cisco IOS XE=17.12.1z5
Cisco IOS XE=17.12.1z6
Cisco IOS XE=17.12.2
Cisco IOS XE=17.12.2a
Cisco IOS XE=17.12.3
Cisco IOS XE=17.12.3a
Cisco IOS XE=17.12.4
Cisco IOS XE=17.12.4a
Cisco IOS XE=17.12.4b
Cisco IOS XE=17.12.5
Cisco IOS XE=17.12.5a
Cisco IOS XE=17.12.5b
Cisco IOS XE=17.12.5c
Cisco IOS XE=17.12.5d
Cisco IOS XE=17.12.6
Cisco IOS XE=17.12.6a
Cisco IOS XE=17.12.6b
Cisco IOS XE=17.12.7
Cisco IOS XE=17.12.7a
Cisco IOS XE=17.12.7b
Cisco IOS XE=17.13.1
Cisco IOS XE=17.13.1a
Cisco IOS XE=17.14.1
Cisco IOS XE=17.14.1a
Cisco IOS XE=17.15.1
Cisco IOS XE=17.15.1a
Cisco IOS XE=17.15.1b
Cisco IOS XE=17.15.1w
Cisco IOS XE=17.15.1x
Cisco IOS XE=17.15.1y
Cisco IOS XE=17.15.2
Cisco IOS XE=17.15.2a
Cisco IOS XE=17.15.2b
Cisco IOS XE=17.15.2c
Cisco IOS XE=17.15.3
Cisco IOS XE=17.15.3a
Cisco IOS XE=17.15.3b
Cisco IOS XE=17.15.4
Cisco IOS XE=17.15.4a
Cisco IOS XE=17.15.4b
Cisco IOS XE=17.15.4c
Cisco IOS XE=17.15.4d
Cisco IOS XE=17.15.4s1
Cisco IOS XE=17.15.5
Cisco IOS XE=17.15.5a
Cisco IOS XE=17.16.1
Cisco IOS XE=17.16.1a
Cisco IOS XE=17.17.1
Cisco IOS XE=17.18.1
Cisco IOS XE=17.18.1a
Cisco IOS XE=17.18.1w
Cisco IOS XE=17.18.1x
Cisco IOS XE=17.18.1y
Cisco IOS XE=17.18.1z
Cisco IOS XE=17.18.2
Cisco IOS XE=17.18.3
Cisco IOS XE=17.18.3a
Cisco IOS XE=26.1.1
Cisco IOS XE=26.1.1a
Cisco IOS XE=26.2.1ea
Event History
Aug 5, 2026
CVE Published
via MITRE·04:28 PM
Data Sourced
via MITRE·04:28 PM
DescriptionSeverityWeakness
Data Sourced
via NVD·05:16 PM
DescriptionSeverityWeaknessAffected Software
Frequently Asked Questions
1
What is the severity of CVE-2026-20301?
CVE-2026-20301 has a high severity rating of 8.6.
2
How do I fix CVE-2026-20301?
To mitigate CVE-2026-20301, upgrade to the latest version of Cisco IOS Software or Cisco IOS XE Software that has addressed this vulnerability.
3
What type of attack does CVE-2026-20301 enable?
CVE-2026-20301 allows an unauthenticated remote attacker to cause a denial of service condition.
4
Which Cisco products are affected by CVE-2026-20301?
CVE-2026-20301 affects Cisco IOS Software and Cisco IOS XE Software that utilize the Extensible Messaging Client Protocol.
5
Is user authentication required to exploit CVE-2026-20301?
No, CVE-2026-20301 can be exploited by unauthenticated attackers.