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Review reviewHigh

CVE-2026-20074

Cisco Cisco IOS XR Software, ios xr

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 adver...

CVSS
7.4
EPSS
0.16%
5.64% percentile
CISA KEV
Not listed
Published
2026.03.12
PRIORITY ASSESSMENT

Review review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV
Exploit probability0.16%
Technical severityCVSS 7.4

Vulnerability overview

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 adver...

Affected product and versions

Product
Cisco Cisco IOS XR Software, ios xr
Affected versions
7.8.1, 7.9.1, 7.10.1, 7.8.2, 7.8.22, 7.9.2, 7.11.1, 7.9.21, 7.10.2, 24.1.1, 7.11.2, 24.2.1, 24.1.2, 24.2.11, 24.3.1, 24.4.1, 24.2.2, 7.8.23, 7.11.21, 24.2.20
Fixed versions
25.2.2

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide
  1. 1
    Identify

    Confirm that Cisco Cisco IOS XR Software, ios xr and an affected version are present.

  2. 2
    Prioritize

    Combine exploitation signals with asset exposure and business criticality.

  3. 3
    Remediate

    Follow the vendor advisory or supported update path and preserve rollback options.

  4. 4
    Verify

    Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
CWE
CWE-1287