CVE-2026-20301: A vulnerability in the Extensible Messaging Client Protocol (XMCP), also referred to as the External Client pr

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HIGH 8.6REMOTEMITIGATEMITIGATE

CVE-2026-20301 is a high-severity flaw (CVSS 8.6) affecting ios, ios xe. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 affec

Why this priority

High severity
Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	8.6 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.6% (top 53%)
CISA exploited list	No
Weakness	CWE-606
Published	2026-08-05
Last modified	2026-09-17

Publisher (CNA): Cisco Systems, Inc. · Vendor: cisco

Last updated 2026-09-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-08-05 17:16 UTCPublished CVE record published
2026-09-17 18:05 UTCUpdated Record last modified

cisco ios MITIGATE

Affected: 15.2\(1\)sy6 · 15.2\(1\)sy7 · 15.2\(1\)sy8 · 15.2\(2\)e8 · 15.2\(2\)e9 · 15.2\(2\)e9a · 15.2\(2\)e10 · 15.2\(2\)e10a

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

cisco ios xe MITIGATE

Affected: 3.8.10ce · 3.8.10de · 3.11.3ae · 3.11.3e · 3.11.4e · 3.11.5e · 3.11.6e · 3.11.7e

Fixed in: no fixed release known

Safe to downgrade to: a release before 3.8.10ce

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-20301?

ios: mitigate or apply the listed mitigation; ios xe: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-20301 being exploited?

CVE-2026-20301 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-20301 affect?

CVE-2026-20301 affects ios, ios xe. Severity is high (CVSS 8.6). 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 servi

How urgent is CVE-2026-20301?

Priority 47/100. High severity; Remotely exploitable, no login, no user action

Software pages

iOS vulnerabilities · Cisco IOS XE vulnerabilities · Cisco vulnerabilities

References

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