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Vulnerability Details CVE-2026-20074

A vulnerability in the Intermediate System-to-Intermediate System (IS-IS) multi-instance routing feature of Cisco IOS XR Software could allow an unauthenticated, adjacent attacker to cause the IS-IS process to restart unexpectedly. This vulnerability is due to insufficient input validation of ingress IS-IS packets. An attacker could exploit this vulnerability by sending crafted IS-IS packets to an affected device after forming an adjacency. A successful exploit could allow the attacker to cause the IS-IS process to restart unexpectedly, resulting in a temporary loss of connectivity to advertised networks and a denial of service (DoS) condition. Note: The IS-IS protocol is a routing protocol. To exploit this vulnerability, an attacker must be Layer 2-adjacent to the affected device and must have formed an adjacency.  

Exploit prediction scoring system (EPSS) score

EPSS Score 0.002

EPSS Ranking 5.6%

CVSS Severity

CVSS v3 Score 7.4

References

https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-isis-dos-kDMxpSzK

Products affected by CVE-2026-20074

Cisco » Ios Xr » Version: 12.4

cpe:2.3:o:cisco:ios_xr:12.4
Cisco » Ios Xr » Version: 15.4(3)m4.1

cpe:2.3:o:cisco:ios_xr:15.4(3)m4.1
Cisco » Ios Xr » Version: 24.1.1

cpe:2.3:o:cisco:ios_xr:24.1.1
Cisco » Ios Xr » Version: 24.1.2

cpe:2.3:o:cisco:ios_xr:24.1.2
Cisco » Ios Xr » Version: 24.2

cpe:2.3:o:cisco:ios_xr:24.2
Cisco » Ios Xr » Version: 24.2.1

cpe:2.3:o:cisco:ios_xr:24.2.1
Cisco » Ios Xr » Version: 24.2.11

cpe:2.3:o:cisco:ios_xr:24.2.11
Cisco » Ios Xr » Version: 24.2.2

cpe:2.3:o:cisco:ios_xr:24.2.2
Cisco » Ios Xr » Version: 24.2.20

cpe:2.3:o:cisco:ios_xr:24.2.20
Cisco » Ios Xr » Version: 24.2.21

cpe:2.3:o:cisco:ios_xr:24.2.21
Cisco » Ios Xr » Version: 24.3

cpe:2.3:o:cisco:ios_xr:24.3
Cisco » Ios Xr » Version: 24.3.1

cpe:2.3:o:cisco:ios_xr:24.3.1
Cisco » Ios Xr » Version: 24.3.2

cpe:2.3:o:cisco:ios_xr:24.3.2
Cisco » Ios Xr » Version: 24.3.20

cpe:2.3:o:cisco:ios_xr:24.3.20
Cisco » Ios Xr » Version: 24.3.30

cpe:2.3:o:cisco:ios_xr:24.3.30
Cisco » Ios Xr » Version: 24.4

cpe:2.3:o:cisco:ios_xr:24.4
Cisco » Ios Xr » Version: 24.4.1

cpe:2.3:o:cisco:ios_xr:24.4.1
Cisco » Ios Xr » Version: 24.4.10

cpe:2.3:o:cisco:ios_xr:24.4.10
Cisco » Ios Xr » Version: 24.4.15

cpe:2.3:o:cisco:ios_xr:24.4.15
Cisco » Ios Xr » Version: 24.4.2

cpe:2.3:o:cisco:ios_xr:24.4.2
Cisco » Ios Xr » Version: 24.4.30

cpe:2.3:o:cisco:ios_xr:24.4.30
Cisco » Ios Xr » Version: 25.1.1

cpe:2.3:o:cisco:ios_xr:25.1.1
Cisco » Ios Xr » Version: 25.1.2

cpe:2.3:o:cisco:ios_xr:25.1.2
Cisco » Ios Xr » Version: 25.1.30

cpe:2.3:o:cisco:ios_xr:25.1.30
Cisco » Ios Xr » Version: 25.2.1

cpe:2.3:o:cisco:ios_xr:25.2.1
Cisco » Ios Xr » Version: 25.3.0

cpe:2.3:o:cisco:ios_xr:25.3.0
Cisco » Ios Xr » Version: 7.10

cpe:2.3:o:cisco:ios_xr:7.10
Cisco » Ios Xr » Version: 7.10.1

cpe:2.3:o:cisco:ios_xr:7.10.1
Cisco » Ios Xr » Version: 7.10.2

cpe:2.3:o:cisco:ios_xr:7.10.2
Cisco » Ios Xr » Version: 7.11

cpe:2.3:o:cisco:ios_xr:7.11
Cisco » Ios Xr » Version: 7.11.1

cpe:2.3:o:cisco:ios_xr:7.11.1
Cisco » Ios Xr » Version: 7.11.2

cpe:2.3:o:cisco:ios_xr:7.11.2
Cisco » Ios Xr » Version: 7.11.21

cpe:2.3:o:cisco:ios_xr:7.11.21
Cisco » Ios Xr » Version: 7.8.1

cpe:2.3:o:cisco:ios_xr:7.8.1
Cisco » Ios Xr » Version: 7.8.12

cpe:2.3:o:cisco:ios_xr:7.8.12
Cisco » Ios Xr » Version: 7.8.2

cpe:2.3:o:cisco:ios_xr:7.8.2
Cisco » Ios Xr » Version: 7.8.22

cpe:2.3:o:cisco:ios_xr:7.8.22
Cisco » Ios Xr » Version: 7.8.23

cpe:2.3:o:cisco:ios_xr:7.8.23
Cisco » Ios Xr » Version: 7.9

cpe:2.3:o:cisco:ios_xr:7.9
Cisco » Ios Xr » Version: 7.9.0

cpe:2.3:o:cisco:ios_xr:7.9.0
Cisco » Ios Xr » Version: 7.9.1

cpe:2.3:o:cisco:ios_xr:7.9.1
Cisco » Ios Xr » Version: 7.9.2

cpe:2.3:o:cisco:ios_xr:7.9.2
Cisco » Ios Xr » Version: 7.9.21

cpe:2.3:o:cisco:ios_xr:7.9.21

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Vulnerability Details CVE-2026-20074

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