iOSOperating system · Cisco
CVE-2013-5480
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 CSCuf28733.
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 exists in Cisco IOS versions 12.2 and 15.0-15.3 where the DNS-over-TCP implementation fails to properly handle crafted IPv4 DNS TCP streams when Network Address Translation (NAT) is in use. A remote attacker can send specially crafted DNS TCP packets that cause the affected device to reload, 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
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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Identify the Cisco IOS versionExecute 'show version' or 'show running-config | include version' to retrieve the installed IOS versionAffected if The version displayed is 12.2, 15.0, 15.1, 15.2, or 15.3 (any release within these major/minor branches)
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Verify NAT is enabled on the deviceExecute 'show ip nat statistics' or 'show running-config | include ip nat' to check if Network Address Translation is configuredAffected if NAT is active or configured on any interface (the vulnerability only triggers when NAT is in use)
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Confirm DNS-over-TCP handling is enabledExecute 'show running-config | include dns' or check for 'ip dns server' / 'ip name-server' in the configuration to see if the device is acting as a DNS server or proxyAffected if The device is configured as a DNS server, DNS proxy, or forwards DNS queries over TCP (ip dns server command present)
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Check for DNS TCP traffic processingReview interface configurations and access-lists for DNS (port 53) TCP traffic entering or being processed by the deviceAffected if The device accepts or processes DNS-over-TCP traffic from external or untrusted networks
The device is affected if it runs a vulnerable IOS version (12.2, 15.0-15.3), has NAT enabled, and handles DNS-over-TCP traffic (as DNS server/proxy or forwarder) where crafted packets could be received.
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 Cisco IOS to a patched version that addresses Bug ID CSCuf28733. If immediate patching is not possible, consider filtering or rate-limiting external DNS-over-TCP traffic at network boundaries and reviewing NAT configurations to limit exposure.
Fix this in iOS
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-2013-5480 — 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-2013-5480 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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