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iOSOperating system · Cisco

CVE-2015-4200

HIGH · 7.8 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 →
87/100
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
Memory leak 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 (memory consumption) by triggering an error during CPE negotiation, aka Bug ID CSCug00885.

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 memory leak exists in Cisco IOS 15.3S within the Performance Routing Engine (PRE) module on UBR devices. The vulnerability is in the IPv6-to-IPv4 functionality and is triggered when an error occurs during CPE (Customer Premises Equipment) negotiation. Remote attackers can exploit this by causing repeated negotiation errors, leading to memory exhaustion and denial of service.

MitigationApply the Cisco IOS 15.3S patch or upgrade to a fixed version that addresses Bug ID CSCug00885. If immediate patching is not feasible, consider isolating affected UBR devices or implementing network-level controls to limit CPE negotiation attempts from untrusted sources.

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:= 15.3\(3\)s= 15.3s

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
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 checks

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

  1. Identify device model
    Run 'show version' or 'show hardware' and look for UBR platform identifiers (e.g., UBR10012, UBR7200, UBR10K) in the output
    Affected if Device is not a Cisco UBR series cable termination system
  2. Check IOS version
    Run 'show version' and examine the firmware version string. Look for version 15.3S or 15.3(3)S
    Affected if IOS version matches 15.3S family (specifically 15.3(3)S or any 15.3S release)
  3. Verify PRE module status
    Run 'show module' or 'show diagnostic result' to confirm the Performance Routing Engine module is present and loaded on the device
    Affected if PRE module is installed and active on the UBR device
  4. Check IPv6 configuration
    Run 'show running-config | include ipv6' or 'show ipv6 interface' to see if IPv6 is enabled on any interfaces
    Affected if IPv6 is configured and operational on the device
  5. Monitor memory usage
    Run 'show memory summary' or 'show process memory' repeatedly over time to observe if memory is steadily decreasing without recovery
    Affected if Memory allocation shows continuous growth or failure to reclaim during CPE negotiation events

A Cisco UBR device running IOS 15.3S with an active PRE module and IPv6 enabled is potentially vulnerable if CPE negotiation errors are occurring and causing memory exhaustion.

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

Apply the Cisco IOS 15.3S patch or upgrade to a fixed version that addresses Bug ID CSCug00885. If immediate patching is not feasible, consider isolating affected UBR devices or implementing network-level controls to limit CPE negotiation attempts from untrusted sources.

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-2015-4200 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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