dbcve.org
Ios XrOperating system · Cisco

CVE-2024-20406

HIGH · 7.4 CVSS v3.1 Published 2024-09-11
Fix available
A fix is available. Upgrade to 7.0.0 / 7.11.2 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 segment routing feature for the Intermediate System-to-Intermediate System (IS-IS) protocol of Cisco IOS XR Software could allow an unauthenticated, adjacent attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to insufficient input validation of ingress IS-IS packets. An attacker could exploit this vulnerability by sending specific IS-IS packets to an affected device after forming an adjacency. A successful exploit could allow the attacker to cause the IS-IS process on all affected devices that are participating in the Flexible Algorithm to crash and restart, resulting in a 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. This vulnerability affects segment routing for IS-IS over IPv4 and IPv6 control planes as well as devices that are configured as level 1, level 2, or multi-level routing IS-IS type.

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

A vulnerability in Cisco IOS XR Software's segment routing for IS-IS protocol allows an adjacent, unauthenticated attacker who has formed an IS-IS adjacency to send specially crafted IS-IS packets that exploit insufficient input validation, causing the IS-IS process to crash and restart and resulting in a DoS condition.

MitigationApply Cisco's IOS XR software update when available; until then, limit Layer 2 adjacency to trusted devices or disable IS-IS segment routing if not required.

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:>= 6.8.1, < 7.0.0>= 7.4.1, < 7.11.2

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 IOS XR version
    Run 'show version' or 'admin show version' on the Cisco device to obtain the installed IOS XR software version number.
    Affected if The version falls within >= 6.8.1 but < 7.0.0, or >= 7.4.1 but < 7.11.2.
  2. Verify IS-IS protocol is enabled
    Run 'show isis protocol' or check the device configuration for 'router isis' under the global configuration mode.
    Affected if IS-IS routing protocol is actively configured and running on the device.
  3. Confirm IS-IS segment routing is configured
    Run 'show isis segment-routing' or inspect the IS-IS router configuration for 'segment-routing' under the IS-IS process.
    Affected if Segment routing is enabled within the IS-IS configuration.
  4. Check IS-IS adjacency exposure
    Run 'show isis adjacency' to list all neighboring devices that have formed IS-IS adjacencies. Evaluate whether Layer 2 adjacency is limited to trusted devices only.
    Affected if Untrusted or unknown devices have formed IS-IS adjacencies, exposing the device to adjacent attackers.

The device is affected if it runs a vulnerable IOS XR version (6.8.1 to <7.0.0 or 7.4.1 to <7.11.2), has IS-IS with segment routing enabled, and has untrusted adjacent neighbors in the IS-IS adjacency table.

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.

From vendor data
Upgrade available Upgrade to 7.0.0 / 7.11.2 or later
Fixed in 7.0.07.11.2
Interim mitigation

Apply Cisco's IOS XR software update when available; until then, limit Layer 2 adjacency to trusted devices or disable IS-IS segment routing if not required.

Fix this in Ios Xr Scoped from the published advisory
  • Consultation5.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA3.0 h
20.0 hours of engineering $3,580
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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-2024-20406 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