iOSOperating system · Cisco
CVE-2013-5479
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 · uneditedThe DNS-over-TCP implementation in Cisco IOS 12.2 and 15.0 through 15.3, when NAT is used, allows remote attackers to cause a denial of service (device reload) via a crafted IPv4 DNS TCP stream, aka Bug ID CSCtn53730.
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 confidenceA vulnerability in Cisco IOS DNS-over-TCP handling allows remote attackers to cause device reloads via crafted IPv4 DNS TCP streams when Network Address Translation (NAT) is in use. The flaw affects IOS versions 12.2 and 15.0 through 15.3, enabling attackers to trigger a denial of service without authentication.
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
iOSOperating system
= 12.2= 15.0= 15.1= 15.2= 15.3CVSS 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
- Authentication
- None
- Confidentiality
- None
- Integrity
- None
- Availability
- Complete
AV:N/AC:L/Au:N/C:N/I:N/A:C
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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Check the Cisco IOS versionRun the 'show version' command on the device and locate the version number in the output (typically on the first line)Affected if The version shown is 12.2, 15.0, 15.1, 15.2, or 15.3 (or falls within these release trains)
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Verify NAT is configuredRun 'show running-config | include ip nat' or 'show ip nat statistics' to check for NAT configurationAffected if NAT is actively configured or running on the device
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Confirm DNS over TCP handling is enabledRun 'show running-config | include dns' and look for 'ip dns server' or DNS-related service configurationAffected if DNS server or DNS forwarding features are enabled in the configuration
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Check for IPv4 DNS TCP traffic processingReview interface configurations for NAT rules that process DNS traffic, or monitor with 'debug ip packet detail' briefly to observe DNS TCP packet handlingAffected if The device is processing or configured to process IPv4 DNS TCP streams through NAT
The device is affected if it runs an IOS version 12.2, 15.0, 15.1, 15.2, or 15.3 AND has NAT enabled AND handles DNS over TCP traffic.
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 dataUpgrade affected Cisco IOS devices to a patched version provided by Cisco. If immediate patching is not possible, consider filtering DNS TCP traffic at network boundaries or disabling NAT for DNS traffic where feasible.
Fix this in iOS
Scoped from the published advisory
- Consultation4.0 h
- Implementation8.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,120.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2013-5479 — 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-2013-5479 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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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.
- 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
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