iOSOperating system · Cisco
CVE-2015-4199
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 · uneditedRace condition in the IPv6-to-IPv4 functionality in Cisco IOS 15.3S in the Performance Routing Engine (PRE) module on UBR devices allows remote attackers to cause a denial of service (NULL pointer free and module crash) by triggering intermittent connectivity with many IPv6 CPE devices, aka Bug ID CSCug47366.
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 confidenceRace condition in the IPv6-to-IPv4 functionality in Cisco IOS 15.3S in the Performance Routing Engine (PRE) module on UBR devices allows remote attackers to cause a NULL pointer dereference leading to module crash and denial of service by triggering intermittent connectivity with many IPv6 CPE devices.
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
= 15.3sCVSS 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
- M
- Authentication
- None
- Confidentiality
- None
- Integrity
- None
- Availability
- Complete
AV:N/AC:M/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' on the device CLI and locate the version string in the outputAffected if The version shown is exactly 15.3S (or a specific 15.3Sx release that falls within the 15.3S train)
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Confirm the device is a UBR platformExecute 'show version' or 'show platform' and check the hardware platform type; UBR devices are cable broadband routersAffected if The device model is a UBR-series router (e.g., UBR10012, UBR7200)
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Verify IPv6-to-IPv4 feature is configuredCheck the running configuration with 'show running-config' for IPv6 transition features such as NAT64, 464XLAT, or IPv6 tunnel interfacesAffected if IPv6-to-IPv4 translation or tunneling features are enabled in the configuration
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Check for Performance Routing Engine (PRE) module usageExecute 'show module' or 'show platform' to verify the PRE module is present and active on the UBR deviceAffected if The PRE module is installed and running on the device
A user is affected if they are running Cisco IOS 15.3S on a UBR device with an active PRE module and IPv6-to-IPv4 translation features enabled, as the race condition triggers when intermittent IPv6 CPE connectivity occurs.
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 the Cisco IOS 15.3S security update addressing CSCug47366. As an interim measure, limit exposure of affected UBR devices and monitor for signs of the described attack pattern involving intermittent IPv6 CPE connectivity.
Fix this in iOS
Scoped from the published advisory
- Consultation6.0 h
- Implementation12.0 h
- Testing6.0 h
- Review / QA3.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2015-4199 — 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-2015-4199 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
- No weaponised exploit code, or anything meant to cause harm
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