Carrier Routing SystemApplication · Cisco
CVE-2016-6401
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 · uneditedCisco Carrier Routing System (CRS) 5.1 and 5.1.4, as used in CRS Carrier Grade Services for CRS-1 and CRS-3 devices, allows remote attackers to cause a denial of service (line-card reload) via crafted IPv6-over-MPLS packets, aka Bug ID CSCva32494.
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 confidenceA remote attacker can send specially crafted IPv6-over-MPLS packets to a vulnerable Cisco CRS (Carrier Routing System) device running versions 5.1 or 5.1.4. The malformed packets trigger a fault in the packet processing path, causing the line card to reload and resulting in denial of service.
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
Carrier Routing SystemApplication
= 5.1.4= 5.1_baseCVSS 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
- High
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.0/AV:A/AC:H/PR:N/UI:N/S:U/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 checksWork through these to decide whether this CVE applies to you.
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Confirm Cisco CRS modelRun 'show platform' or 'show version' on the device CLI to identify the hardware model. Look for 'CRS' in the product name or description.Affected if The device is not a Cisco CRS (Carrier Routing System)
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Check CRS software versionRun 'show version' and locate the IOS XR version string. Compare it against 5.1.4 or 5.1_base.Affected if The running version equals 5.1.4 or 5.1_base specifically
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Verify IPv6-over-MPLS is enabledRun 'show mpls interfaces' and 'show ipv6 interface' to check if IPv6 is configured over any MPLS-enabled interfaces. Also check configuration with 'show run | include ipv6' and 'show run | include mpls'.Affected if IPv6 is configured and operational over MPLS-enabled interfaces
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Review line card reload historyRun 'show logging' or 'show install log' and look for recent reload events, crash logs, or MPLS-related errors. Check 'show platform' for any line cards in degraded state.Affected if Recent unexpected line card reloads or MPLS packet processing faults are logged
The environment is affected only if the device is a Cisco CRS running version 5.1.4 or 5.1_base with IPv6-over-MPLS actively configured and operational.
Generated from the published advisory. Verify against your own configuration.
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 dataApply Cisco security updates for CRS versions 5.1 and 5.1.4 when available; consider filtering IPv6-over-MPLS traffic at network boundaries if not required, and implement traffic monitoring for anomalous MPLS patterns.
Fix this in Carrier Routing System
Scoped from the published advisory
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA4.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2016-6401 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2016-6401 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
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