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8.6
CVE-2026-20301
Cisco · Cisco IOS XE Software

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.

Affected Products

VendorProductVersions
CiscoCisco IOS XE Software17.2.1a, 16.12.1y, 16.12.3s, 16.7.1b, 16.6.2, 16.6.5, 16.12.1w, 16.9.1d, 17.3.1, 16.9.4c, 16.7.1, 17.2.1, 16.6.8, 16.9.1b, 16.9.2s, 16.12.4, 16.12.3a, 17.1.1s, 16.11.1a, 16.7.2, 16.11.1b, 16.9.1s, 16.9.3h, 16.9.1c, 16.6.5a, 16.6.3, 16.10.1f, 17.2.1v, 16.8.1e, 16.9.3a, 16.12.1a, 16.12.1x, 3.16.10aS, 16.6.4s, 16.10.1c, 16.12.3, 16.11.2, 16.6.5b, 16.12.2s, 16.10.1b, 16.7.3, 16.6.7, 16.9.6, 16.9.2, 16.10.1, 16.12.1t, 16.9.1, 16.8.1a, 3.18.8aSP, 16.9.3s, 16.6.7a, 16.12.2, 16.11.1, 16.9.3, 16.11.1s, 16.12.1, 17.1.1, 17.1.2, 16.10.1d, 17.1.1t, 16.9.4, 16.8.3, 16.12.2t, 16.9.5, 16.8.1s, 16.10.1e, 16.8.2, 16.6.4, 16.8.1b, 16.10.1a, 16.12.1z, 16.8.1c, 16.9.1a, 16.9.5f, 16.6.4a, 16.10.1g, 16.8.1, 16.6.6, 16.9.2a, 16.8.1d, 16.10.3, 16.7.1a, 16.11.1c, 16.10.1s, 17.2.1r, 17.1.1a, 16.10.2, 16.12.2a, 16.12.1c, 16.12.1s, 16.7.4, 3.18.9SP, 17.2.2, 3.11.3E, 16.9.8, 16.9.7, 17.1.3, 17.3.1a, 3.11.4E, 17.3.2a, 16.12.5, 17.3.1w, 17.3.2, 3.11.3aE, 17.4.1, 16.12.4a, 17.4.1a, 3.16.10bS, 17.3.1x, 17.3.3, 16.6.9, 17.2.3, 17.5.1, 16.12.1z1, 16.12.5a, 17.4.1b, 17.3.1z, 16.12.5b, 17.4.2, 17.3.3a, 3.11.5E, 17.3.5, 17.3.4, 17.5.1a, 16.12.6, 17.6.1, 16.12.1z2, 16.6.10, 17.3.4a, 17.6.1a, 3.8.10cE, 17.7.1, 17.6.1x, 17.6.2, 16.12.6a, 17.3.4c, 17.4.2a, 17.3.4b, 17.7.1a, 16.12.7, 17.8.1a, 17.6.3a, 17.6.3, 17.7.2, 17.7.1b, 17.9.1w, 17.3.5a, 17.6.1z, 3.8.10dE, 16.12.8, 17.8.1, 17.9.1, 3.11.6E, 17.6.4, 3.11.7E, 17.3.5b, 17.9.1a, 17.3.6, 17.10.1, 3.11.8E, 16.9.8a, 17.6.1z1, 17.10.1a, 17.9.2, 17.6.5, 17.9.1x, 17.9.1y, 16.9.8b, 17.3.7, 17.9.2a, 17.9.3, 16.12.9, 17.11.1, 17.10.1b, 17.6.6, 17.9.1x1, 17.11.1a, 17.9.3a, 17.12.1, 17.3.8, 17.9.4, 16.12.10, 17.12.1w, 17.9.1y1, 17.12.1a, 3.11.9E, 17.9.5, 17.13.1, 17.12.1x, 17.12.2, 17.14.1, 17.9.4a, 17.3.8a, 17.6.6a, 17.6.5a, 17.6.7, 16.12.10a, 17.15.1, 17.13.1a, 17.12.2a, 16.12.11, 17.12.3, 17.12.1y, 3.11.10E, 17.12.1z, 17.9.5a, 17.14.1a, 17.9.5b, 17.6.8, 16.12.12, 17.12.4, 17.9.6, 17.17.1, 17.16.1, 17.15.1w, 17.12.3a, 3.11.11E, 17.9.5c, 17.15.1a, 17.12.1z1, 17.15.2, 17.15.1b, 17.9.5d, 17.15.1x, 17.9.6a, 17.12.1z2, 17.6.8a, 17.16.1a, 16.12.13, 17.15.3, 17.9.7, 17.12.5, 17.15.1y, 17.9.5e, 17.12.4a, 17.15.2a, 17.15.2c, 17.15.2b, 17.12.1z3, 17.9.5f, 17.12.4b, 3.11.12E, 17.12.5a, 17.18.1, 17.12.6, 17.12.1z4, 17.9.8, 17.9.7a, 17.15.3a, 17.15.4, 3.11.13E, 17.12.5b, 17.15.3b, 16.12.14, 17.18.1z, 17.9.7b, 17.12.5c, 26.1.1, 17.18.1a, 17.15.4a, 17.18.2, 17.18.1w, 17.15.4b, 17.12.6a, 17.12.7, 17.15.4c, 17.9.9, 17.12.5d, 16.12.15, 17.15.4s1, 17.15.5, 17.12.1z5, 17.18.1x, 17.12.1z6, 17.15.4d, 17.12.6b, 17.4.1c, 3.11.14E, 17.15.5a, 17.18.1y, 17.12.7a, 17.18.3, 17.12.7b, 17.18.3a, 26.1.1a, 26.2.1ea, 16.12.16, 15.2(7)E7, 15.2(8)E3, 15.7(3)M10, 15.8(3)M9, 15.9(3)M7, 15.2(7)E8, 15.2(8)E4, 15.9(3)M7a, 15.2(2)E10c, 15.2(4)E10d, 15.9(3)M6a, 15.9(3)M6b, 15.5(1)SY10, 15.5(1)SY11, 15.2(6)E1a, 15.4(1)SY4, 15.5(1)SY1, 15.2(2)E8, 15.2(6)E1, 15.7(3)M2, 15.2(4)E6, 15.2(1)SY6, 15.2(4)EA7, 15.2(6)E1s, 15.7(3)M3, 15.8(3)M, 15.2(1)SY7, 15.2(4)EA8, 15.8(3)M0a, 15.2(2)E9, 15.2(6)E2, 15.5(1)SY2, 15.2(4)E7, 15.2(6)E2a, 15.2(2)E9a, 15.8(3)M0b, 15.2(6)E2b, 15.8(3)M1, 15.8(3)M1a, 15.7(3)M4, 15.2(1)SY8, 15.2(4)E8, 15.5(1)SY3, 15.2(7)E, 15.7(3)M4a, 15.8(3)M2, 15.2(7)E0a, 15.8(3)M2a, 15.7(3)M4b, 15.2(2)E10, 15.2(7)E0s, 15.2(4)EA9, 15.2(7)E0b, 15.2(6)E3, 15.9(3)M, 15.8(3)M3, 15.5(1)SY4, 15.7(3)M5, 15.2(2)E10a, 15.2(4)E9, 15.2(7)E1, 15.8(3)M3b, 15.9(3)M0a, 15.2(7)E1a, 15.2(4)E10, 15.5(1)SY5, 15.2(4)EA9a, 15.9(3)M1, 15.8(3)M4, 15.7(3)M6, 15.2(7)E2, 15.5(1)SY6, 15.2(7)E3, 15.8(3)M5, 15.7(3)M7, 15.9(3)M2, 15.2(7)E2b, 15.9(3)M2a, 15.2(4)E10a, 15.2(7)E4, 15.5(1)SY7, 15.2(4)E10b, 15.2(7)E3k, 15.2(8)E, 15.9(3)M3, 15.8(3)M6, 15.7(3)M8, 15.8(3)M7, 15.5(1)SY8, 15.2(7)E5, 15.2(8)E1, 15.9(3)M4, 15.2(8)E2, 15.2(4)E10c, 15.7(3)M9, 15.2(2)E10b, 15.2(7)E6, 15.9(3)M4a, 15.5(1)SY9, 15.9(3)M5, 15.8(3)M8, 15.9(3)M6, 15.9(3)M9, 15.5(1)SY13, 15.9(3)M8b, 15.2(7)E9, 15.5(1)SY12, 15.7(3)M10a, 15.9(3)M8, 15.9(3)M8a, 15.2(8)E5, 15.2(7)E10, 15.7(3)M10b, 15.9(3)M3a, 15.8(3)M3a, 15.9(3)M3b, 15.6(2)SP7, 15.6(2)SP5, 15.6(2)SP8, 15.6(2)SP6, 15.6(2)SP4, 15.6(2)SP9, 15.6(2)SP8a, 15.9(3)M9a, 15.2(8)E6, 15.9(3)M10, 15.2(7)E11, 15.5(1)SY14, 15.2(8)E7, 15.2(4)E10e, 15.9(3)M11, 15.2(7)E12, 15.5(1)SY15, 15.2(8)E8, 15.5(1)SY16, 15.2(7)E13, 15.9(3)M12, 15.5(1)SY17, 15.2(7)E14, 15.9(3)M13

Also Affects

Downstream vendors/products affected by this vulnerability

VendorProductSourceConfidence
ciscisco ios xecert_advisory90%
cisiosmitre_affected90%
ciscisco ioscert_advisory90%

References

  • https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ios-xmcp-thbAr34t

Related News (4 articles)

Tier B
BSI Advisories2d ago
[NEU] [hoch] Cisco IOS: Schwachstelle ermöglicht Denial of Service
→ No new info (linked only)
Tier B
CERT-FR3d ago
Multiples vulnérabilités dans les produits Cisco (06 août 2026)
→ No new info (linked only)
Tier C
VulDB3d ago
CVE-2026-20301 | Cisco IOS XE Software/IOS XMCP denial of service
→ No new info (linked only)
Tier A
Cisco Security3d ago
Cisco IOS Software and IOS XE Software Extensible Messaging Client Protocol Denial of Service Vulnerability
→ No new info (linked only)
CVSS 3.18.6 HIGH
VectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
CISA KEV❌ No
Actively exploited❌ No
CWECWE-606
PublishedAug 5, 2026
Last enriched3d ago
Trending Score40
Source articles4
Independent4
Info Completeness8/14
Missing: epss, kev, exploit, patch, iocs, mitre_attack

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Verification

State: verified
Confidence: 0%

Vulnerability Timeline

CVE Published
Aug 5, 2026
Discovered by ZDM
Aug 5, 2026