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Ios XrOperating system · Cisco

CVE-2015-4205

MEDIUM · 5.7 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 →
62/100
Remediation priority · Elevated
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
Cisco IOS XR 5.3.1 on ASR 9000 devices allows remote attackers to cause a denial of service (NPU chip reset or line-card reload) by sending crafted IEEE 802.3x flow-control PAUSE frames on the local network, aka Bug ID CSCut19959.

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 the handling of IEEE 802.3x flow-control PAUSE frames in Cisco IOS XR 5.3.1 on ASR 9000 devices allows remote attackers on the local network to cause denial of service by sending specially crafted PAUSE frames, resulting in NPU chip reset or line-card reload.

MitigationApply the Cisco IOS XR patch for bug ID CSCut19959 to address the flawed PAUSE frame handling; additionally, implement network segmentation and port-level filtering to restrict unauthorized access to vulnerable network segments.

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
Ios XrOperating system
Affected:= 5.3.1

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
Adjacent
Complexity
M
Authentication
None
Confidentiality
None
Integrity
None
Availability
Complete

AV:A/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 the device hardware platform
    Run 'show platform' or check the chassis hardware to confirm if the device is an ASR 9000 series router
    Affected if The device is an ASR 9000 series router - this is required for the vulnerability to apply
  2. Check the IOS XR software version
    Run 'show version' or 'admin show version' to display the installed IOS XR version
    Affected if The version displayed is exactly 5.3.1 - this is the only affected version listed
  3. Verify if flow control is enabled on interfaces
    Run 'show controllers <interface> flowcontrol' or 'show interfaces' to check if IEEE 802.3x flow-control is configured on any interface
    Affected if Flow control is enabled on one or more interfaces - the vulnerability requires PAUSE frame handling to be active
  4. Assess local network accessibility
    Review access controls and network segmentation to determine if untrusted local attackers can send frames to the device interfaces
    Affected if The device is accessible to untrusted local attackers who can send crafted Ethernet frames

The environment is affected if the device is an ASR 9000 running exactly IOS XR version 5.3.1 with flow control enabled on accessible interfaces, allowing untrusted local network attackers to send malicious PAUSE frames.

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 XR patch for bug ID CSCut19959 to address the flawed PAUSE frame handling; additionally, implement network segmentation and port-level filtering to restrict unauthorized access to vulnerable network segments.

Fix this in Ios Xr Scoped from the published advisory
  • Consultation4.0 h
  • Implementation6.0 h
  • Testing3.0 h
  • Review / QA2.0 h
15.0 hours of engineering $2,690
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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-2015-4205 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
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data