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iOSOperating system · Cisco

CVE-2012-3950

HIGH · 7.1 CVSS v2.0 Published 2012-09-27
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
80/100
Remediation priority · High
Remotely reachable No privileges Zero-click

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 · unedited
The Intrusion Prevention System (IPS) feature in Cisco IOS 12.3 through 12.4 and 15.0 through 15.2, in certain configurations of enabled categories and missing signatures, allows remote attackers to cause a denial of service (device reload) via DNS packets, aka Bug ID CSCtw55976.

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 confidence

A vulnerability in Cisco IOS Intrusion Prevention System (IPS) feature versions 12.3-12.4 and 15.0-15.2 allows remote attackers to cause device reload via specially crafted DNS packets when certain IPS categories are enabled but corresponding signatures are missing, leading to denial of service.

MitigationEnsure IPS signatures are up-to-date and properly configured; consider disabling IPS or specific DNS inspection categories until patches can be applied; review IPS category configurations to avoid mismatches between enabled categories and installed signatures.

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
Affected:= 12.3= 12.3\(1a\)= 12.3\(2\)ja= 12.3\(2\)ja5= 12.3\(2\)jk= 12.3\(2\)jk1= 12.3\(2\)t3= 12.3\(2\)t8= 12.3\(2\)xa4= 12.3\(2\)xa5= 12.3\(2\)xc1= 12.3\(2\)xc2

CVSS 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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify Cisco IOS version
    Run 'show version' command and locate the IOS release number in the output
    Affected if Version falls within 12.3-12.4 or 15.0-15.2 range
  2. Verify IPS feature is enabled
    Run 'show ip ips' or 'show running-config | include ips' to check if Cisco IPS is configured on the device
    Affected if IPS feature is actively enabled in the device configuration
  3. Confirm DNS inspection category is active
    Run 'show ip ips configuration' or inspect the IPS policy map to see if DNS inspection is among the enabled inspection categories
    Affected if DNS-related IPS category or inspection is explicitly enabled in the IPS policy
  4. Check signature status for DNS signatures
    Run 'show ip ips signature' or 'show ip ips signature count' to examine installed signatures and their states, specifically looking for DNS-related signatures
    Affected if DNS signatures are missing, disabled, or have a version mismatch with enabled categories
  5. Review IPS category-to-signature mapping
    Compare the enabled IPS categories from 'show ip ips configuration' against installed signatures using 'show ip ips signatures' to identify any category where signatures are not present
    Affected if An IPS category is enabled but corresponding signatures are not installed or are inactive

Device is affected if it runs Cisco IOS 12.3-12.4 or 15.0-15.2, has IPS enabled with DNS inspection category active, and is missing corresponding DNS signatures.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Ensure IPS signatures are up-to-date and properly configured; consider disabling IPS or specific DNS inspection categories until patches can be applied; review IPS category configurations to avoid mismatches between enabled categories and installed signatures.

Fix this in iOS Scoped from the published advisory
  • Consultation4.0 h
  • Implementation6.0 h
  • Testing4.0 h
  • Review / QA2.0 h
16.0 hours of engineering $2,840
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2012-3950 in production — separate from our analysis above.

No notes yet

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What this is

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.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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