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Ios XrOperating system · Cisco

CVE-2019-1918

HIGH · 7.4 CVSS v3.1 Published 2019-08-07
Fix available
A fix is available. Upgrade to 6.6.3 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 implementation of Intermediate System–to–Intermediate System (IS–IS) routing protocol functionality in Cisco IOS XR Software could allow an unauthenticated attacker who is in the same IS-IS area to cause a denial of service (DoS) condition. The vulnerability is due to incorrect processing of IS–IS link-state protocol data units (PDUs). An attacker could exploit this vulnerability by sending specific link-state PDUs to an affected system to be processed. A successful exploit could allow the attacker to cause incorrect calculations used in the weighted remote shared risk link groups (SRLG) or in the IGP Flexible Algorithm. It could also cause tracebacks to the logs or potentially cause the receiving device to crash the IS–IS process, resulting in a DoS condition.

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 IS-IS routing protocol implementation allows an unauthenticated attacker within the same IS-IS area to send specially crafted link-state PDUs. This causes incorrect weighted remote SRLG or IGP Flexible Algorithm calculations, potentially triggering tracebacks or crashing the IS-IS process, resulting in denial of service.

MitigationApply the relevant Cisco IOS XR Software security update; until then, limit IS-IS adjacency to trusted peers using authentication or network segmentation to reduce attack surface.

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:>= 6.5.2, < 6.6.3
Carrier Routing SystemOperating system
Affected:= 6.5.1= 6.5.3

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 device platform and OS
    Execute 'show version' or check the system banner to confirm the device runs Cisco IOS XR or Cisco Carrier Routing System
    Affected if The device is not Cisco IOS XR or Cisco CRS (different platforms are not affected)
  2. Determine the installed IOS XR or CRS version
    Run 'show version' and locate the system image version string (e.g., 6.5.3)
    Affected if The version falls within 6.5.2 to 6.6.2 (inclusive) for IOS XR, or is exactly 6.5.1 or 6.5.3 for CRS
  3. Verify IS-IS protocol is configured
    Run 'show isis protocol' or 'show running-config | include isis' to check if IS-IS is enabled on any interface
    Affected if IS-IS is not configured or disabled - the vulnerability requires IS-IS to be actively running
  4. Confirm IS-IS adjacency status
    Run 'show isis adjacency' to see if the device has any IS-IS neighbors in the area
    Affected if The device has active IS-IS adjacencies - exploitation requires an attacker within the same IS-IS area

A device is affected if it runs Cisco IOS XR 6.5.2 through 6.6.2 or CRS 6.5.1/6.5.3 AND has IS-IS protocol enabled with active adjacencies.

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 6.6.3 or later
Fixed in 6.6.3
Interim mitigation

Apply the relevant Cisco IOS XR Software security update; until then, limit IS-IS adjacency to trusted peers using authentication or network segmentation to reduce attack surface.

Fix this in Ios Xr Scoped from the published advisory
  • Consultation6.0 h
  • Implementation12.0 h
  • Testing8.0 h
  • Review / QA4.0 h
30.0 hours of engineering $5,280
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $8,448.

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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-2019-1918 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