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iOSOperating system · Cisco

CVE-2015-4203

MEDIUM · 5.4 CVSS v2.0 Published 2015-06-23
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
63/100
Remediation priority · Elevated
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
Race condition in Cisco IOS 12.2SCH in the Performance Routing Engine (PRE) module on uBR10000 devices, when NetFlow and an MPLS IPv6 VPN are configured, allows remote attackers to cause a denial of service (PXF process crash) by sending malformed MPLS 6VPE packets quickly, aka Bug ID CSCud83396.

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 · moderate confidence

Race condition in Cisco IOS 12.2SCH Performance Routing Engine (PRE) module on uBR10000 devices causes denial of service (PXF process crash) when NetFlow and MPLS IPv6 VPN (6VPE) are both configured, triggered by remote attackers sending malformed MPLS 6VPE packets rapidly.

MitigationUpgrade Cisco IOS to a version beyond 12.2SCH that addresses CSCud83396; if patching is not immediately feasible, consider disabling NetFlow or MPLS 6VPE if either feature is not essential, or implement traffic filtering at network edges to block malformed MPLS packets.

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:= 12.2\(33\)sch= 12.2sch

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
High
Authentication
None
Confidentiality
None
Integrity
None
Availability
Complete

AV:N/AC:H/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. Confirm device is a uBR10000 series router
    Execute 'show version' or 'show hardware' and verify the model number indicates uBR10012 or uBR10000 series
    Affected if Device is not a uBR10000 series router - not affected
  2. Check the IOS version
    Run 'show version' and locate the IOS release string; verify it contains '12.2SCH' or '12.2(33)SCH'
    Affected if IOS version is not in the 12.2SCH train - not affected
  3. Verify NetFlow is enabled
    Run 'show ip flow interface' or examine the running configuration with 'show run | include flow'; look for ip flow-export or ip flow-cache commands
    Affected if NetFlow is not configured on any interface - not affected
  4. Verify MPLS 6VPE is configured
    Examine the running configuration for 'ipv6 vpn' statements under the MPLS section, and check for VRF instances with IPv6 routing enabled using 'show vrf'
    Affected if MPLS 6VPE is not configured - not affected

The device is affected only if it is a uBR10000 running IOS 12.2SCH with BOTH NetFlow and MPLS 6VPE simultaneously enabled.

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

Upgrade Cisco IOS to a version beyond 12.2SCH that addresses CSCud83396; if patching is not immediately feasible, consider disabling NetFlow or MPLS 6VPE if either feature is not essential, or implement traffic filtering at network edges to block malformed MPLS packets.

Fix this in iOS Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA2.0 h
20.0 hours of engineering $3,500
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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-2015-4203 in production — separate from our analysis above.

No notes yet

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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