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Description

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.  

PUBLISHED Reserved 2025-10-08 | Published 2026-03-11 | Updated 2026-03-11 | Assigner cisco




HIGH: 7.4CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

Problem types

Improper Validation of Specified Type of Input

Product status

Default status
unknown

7.8.1
affected

7.9.1
affected

7.10.1
affected

7.8.2
affected

7.8.22
affected

7.9.2
affected

7.11.1
affected

7.9.21
affected

7.10.2
affected

24.1.1
affected

7.11.2
affected

24.2.1
affected

24.1.2
affected

24.2.11
affected

24.3.1
affected

24.4.1
affected

24.2.2
affected

7.8.23
affected

7.11.21
affected

24.2.20
affected

24.3.2
affected

24.4.10
affected

25.1.1
affected

24.4.2
affected

24.3.20
affected

24.4.15
affected

25.2.1
affected

25.1.2
affected

24.3.30
affected

24.4.30
affected

24.2.21
affected

25.2.15
affected

References

sec.cloudapps.cisco.com/...visory/cisco-sa-isis-dos-kDMxpSzK (cisco-sa-isis-dos-kDMxpSzK)

cve.org (CVE-2026-20074)

nvd.nist.gov (CVE-2026-20074)

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