iOSOperating system · Cisco
CVE-2013-5476
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 Zone-Based Firewall (ZFW) feature in Cisco IOS 15.1 through 15.2, when content filtering or HTTP ALG inspection is enabled, allows remote attackers to cause a denial of service (device reload or hang) via crafted IPv4 HTTP traffic, aka Bug ID CSCtx56174.
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 confidenceThe Zone-Based Firewall (ZFW) in Cisco IOS 15.1-15.2 contains a denial-of-service vulnerability when content filtering or HTTP ALG inspection is enabled. Remote attackers can send specially crafted IPv4 HTTP packets to trigger device reload or hang.
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
= 15.1= 15.2CVSS 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 Cisco IOS versionRun 'show version' command on the device CLI and locate the IOS version number in the outputAffected if The version shown is exactly 15.1 or 15.2 (e.g., 15.1(4)M, 15.2(1)T, etc.)
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Confirm Zone-Based Firewall is configuredRun 'show zone-pair security' command to list configured ZFW zone-pairsAffected if Any zone-pairs are listed, indicating ZFW is actively configured on the device
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Check if content filtering is enabled in ZFWRun 'show policy-map type inspect zone-pair' commands or examine the configuration with 'show run | include class-map|type inspect' to locate content filtering settings within ZFW policiesAffected if Content filtering (often identified by 'content-filter' or 'filter' keywords in policy configurations) is configured on any ZFW policy
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Check if HTTP ALG inspection is enabled in ZFWRun 'show run | include class-map|type inspect' and look for HTTP inspection configurations (such as 'inspect http' in policy-map or class-map definitions) applied to ZFW zone-pairsAffected if HTTP ALG inspection (indicated by 'inspect http' in policy configurations) is applied to any ZFW zone-pair
A device is affected if it runs Cisco IOS 15.1 or 15.2 AND has Zone-Based Firewall enabled with either content filtering or HTTP ALG inspection configured on any zone-pair policy.
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 dataDisable content filtering or HTTP ALG inspection in ZFW configuration, or upgrade to a Cisco IOS version that addresses CSCtx56174.
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-2013-5476 — 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-2013-5476 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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