Cisco IOS XR Software Multi-Instance Intermediate System-to-Intermediate System Denial of Service Vulnerability

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Summary

CVECVE-2026-20074
StatePUBLISHED
Assignercisco
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-03-11 17:16:55 UTC
Updated2026-07-08 19:07:12 UTC
DescriptionA 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.  

Risk And Classification

Primary CVSS: v3.1 7.4 HIGH from [email protected]

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

EPSS: 0.001600000 probability, percentile 0.055570000 (date 2026-07-10)

Problem Types: CWE-1287 | CWE-1287 Improper Validation of Specified Type of Input

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.4HIGHCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
3.1CNACVSSV3_17.4HIGHCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Adjacent
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Changed
Confidentiality
None
Integrity
None
Availability
High

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

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Cisco Ios Xr All All All All
Operating System Cisco Ios Xr 25.3.0 All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Cisco Cisco IOS XR Software affected 7.8.1 Not specified
CNA Cisco Cisco IOS XR Software affected 7.9.1 Not specified
CNA Cisco Cisco IOS XR Software affected 7.10.1 Not specified
CNA Cisco Cisco IOS XR Software affected 7.8.2 Not specified
CNA Cisco Cisco IOS XR Software affected 7.8.22 Not specified
CNA Cisco Cisco IOS XR Software affected 7.9.2 Not specified
CNA Cisco Cisco IOS XR Software affected 7.11.1 Not specified
CNA Cisco Cisco IOS XR Software affected 7.9.21 Not specified
CNA Cisco Cisco IOS XR Software affected 7.10.2 Not specified
CNA Cisco Cisco IOS XR Software affected 24.1.1 Not specified
CNA Cisco Cisco IOS XR Software affected 7.11.2 Not specified
CNA Cisco Cisco IOS XR Software affected 24.2.1 Not specified
CNA Cisco Cisco IOS XR Software affected 24.1.2 Not specified
CNA Cisco Cisco IOS XR Software affected 24.2.11 Not specified
CNA Cisco Cisco IOS XR Software affected 24.3.1 Not specified
CNA Cisco Cisco IOS XR Software affected 24.4.1 Not specified
CNA Cisco Cisco IOS XR Software affected 24.2.2 Not specified
CNA Cisco Cisco IOS XR Software affected 7.8.23 Not specified
CNA Cisco Cisco IOS XR Software affected 7.11.21 Not specified
CNA Cisco Cisco IOS XR Software affected 24.2.20 Not specified
CNA Cisco Cisco IOS XR Software affected 24.3.2 Not specified
CNA Cisco Cisco IOS XR Software affected 24.4.10 Not specified
CNA Cisco Cisco IOS XR Software affected 25.1.1 Not specified
CNA Cisco Cisco IOS XR Software affected 24.4.2 Not specified
CNA Cisco Cisco IOS XR Software affected 24.3.20 Not specified
CNA Cisco Cisco IOS XR Software affected 24.4.15 Not specified
CNA Cisco Cisco IOS XR Software affected 25.2.1 Not specified
CNA Cisco Cisco IOS XR Software affected 25.1.2 Not specified
CNA Cisco Cisco IOS XR Software affected 24.3.30 Not specified
CNA Cisco Cisco IOS XR Software affected 24.4.30 Not specified
CNA Cisco Cisco IOS XR Software affected 24.2.21 Not specified
CNA Cisco Cisco IOS XR Software affected 25.2.15 Not specified

References

ReferenceSourceLinkTags
sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-isis-d... [email protected] sec.cloudapps.cisco.com Mitigation, Vendor Advisory
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Additional Advisory Data

Exploits

CNA: The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.

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