dbcve.org
Ios XrOperating system · Cisco

CVE-2026-20074

HIGH · 7.4 CVSS v3.1 Published 2026-03-11
Fix available
A fix is available. Upgrade to 25.2.2 or later.
See remediation →
79/100
Remediation priority · High
No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.  

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

This is a high-severity vulnerability in Cisco IOS XR Software's IS-IS multi-instance routing feature. The flaw stems from insufficient input validation of ingress IS-IS packets, allowing an adjacent, unauthenticated attacker who has formed an IS-IS adjacency to send specially crafted packets that cause the IS-IS process to restart unexpectedly, resulting in a denial of service through loss of connectivity to advertised networks.

MitigationApply the vendor-supplied Cisco IOS XR Software patch when available, and consider network segmentation or ACLs to restrict Layer 2 adjacency to trusted neighbors as a compensating control.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Ios XrOperating system
Affected:>= 7.8.0, < 25.2.2= 25.3.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Adjacent
Complexity
Low
Privileges
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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify the Cisco IOS XR version
    Run 'show version' on the device and locate the IOS XR release version number (e.g., 7.8.1, 24.4.1, 25.3.0)
    Affected if The installed version is greater than or equal to 7.8.0 AND less than 25.2.2, OR equals exactly 25.3.0
  2. Confirm IS-IS routing is enabled
    Run 'show isis interface' or 'show protocols isis' to list active IS-IS instances
    Affected if Any IS-IS instance is configured and running on the device
  3. Verify IS-IS adjacencies are formed
    Run 'show isis adjacency' to display current neighbor adjacencies
    Affected if One or more IS-IS adjacencies to neighboring devices exist (the attacker must be an adjacent neighbor)
  4. Check for IS-IS multi-instance configuration
    Run 'show isis instance' or review the configuration with 'show running-config | include router isis' to identify multi-instance setups
    Affected if Multiple IS-IS instances (multi-instance) are configured

You are affected if the device runs Cisco IOS XR version 7.8.0 through 25.2.1 or exactly 25.3.0, AND has IS-IS enabled with active adjacencies formed with neighboring devices.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 25.2.2 or later
Fixed in 25.2.2
Interim mitigation

Apply the vendor-supplied Cisco IOS XR Software patch when available, and consider network segmentation or ACLs to restrict Layer 2 adjacency to trusted neighbors as a compensating control.

Recommended fix High confidence

Cisco IOS XR 25.2.2 or later (25.4.x and beyond)

  1. Identify the current Cisco IOS XR version using 'show version' command
  2. Schedule a maintenance window as IS-IS process restart will cause temporary connectivity loss
  3. Download Cisco IOS XR software version 25.2.2 or later from Cisco's software download center
  4. Follow Cisco's standard IOS XR upgrade procedure: copy the new image to bootflash, set boot variable, and reload
  5. After reload, verify IS-IS process is running using 'show isis interface' command
  6. Confirm adjacency with neighboring routers using 'show isis neighbor' command
Caveat Standard IOS XR upgrade precautions apply - review release notes for any configuration changes or migration requirements

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Ios Xr Scoped from the published advisory
  • Consultation8.0 h
  • Implementation4.0 h
  • Testing12.0 h
  • Review / QA4.0 h
28.0 hours of engineering $4,840
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Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-20074 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data