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Ios XrOperating system · Cisco

CVE-2016-6421

MEDIUM · 5.3 CVSS v3.0 Published 2016-10-05
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
62/100
Remediation priority · Elevated
Remotely reachable 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
Cisco IOS XR 5.2.2 allows remote attackers to cause a denial of service (process restart) via a crafted OSPF Link State Advertisement (LSA) update, aka Bug ID CSCvb05643.

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 · moderate confidence

A denial of service vulnerability in Cisco IOS XR 5.2.2 allows remote attackers to cause a process restart by sending a crafted OSPF Link State Advertisement (LSA) update. The vulnerability is exploitable without authentication over the network.

MitigationApply the Cisco IOS XR software update that addresses CSCvb05643, or contact Cisco for the appropriate patch. Implement OSPF MD5 authentication to limit attack surface until the patch is applied.

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:= 5.2.2

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
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

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 software version
    Execute 'show version' or 'admin show version' on the IOS XR device CLI to retrieve the running software version
    Affected if The displayed version number is exactly 5.2.2
  2. Confirm OSPF is enabled on the device
    Execute 'show ospf' or 'show ospf interface' in the IOS XR CLI to check if OSPF routing protocol is configured and active
    Affected if OSPF process is running and OSPF interfaces are present
  3. Check OSPF neighbor relationships
    Execute 'show ospf neighbor' to view active OSPF adjacencies
    Affected if There are active OSPF neighbors, indicating the router is processing OSPF LSA updates from other devices
  4. Review OSPF configuration for authentication
    Execute 'show running-config router ospf' to examine OSPF interface authentication settings
    Affected if OSPF authentication is not configured or is set to none ( plaintext), meaning the device accepts unauthenticated OSPF packets

You are affected if your device runs Cisco IOS XR version 5.2.2 and has OSPF enabled, regardless of authentication configuration, since the vulnerability can be exploited over the network without authentication.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the Cisco IOS XR software update that addresses CSCvb05643, or contact Cisco for the appropriate patch. Implement OSPF MD5 authentication to limit attack surface until the patch is applied.

Fix this in Ios Xr Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,080
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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-2016-6421 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