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Ios XrOperating system · Cisco

CVE-2011-0949

HIGH · 7.8 CVSS v2.0 Published 2011-05-31
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
Cisco IOS XR 3.6.x, 3.8.x before 3.8.3, and 3.9.x before 3.9.1 does not properly remove sshd_lock files from /tmp/, which allows remote attackers to cause a denial of service (disk consumption) by making many SSHv1 connections, aka Bug ID CSCtd64417.

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

Cisco IOS XR versions 3.6.x, 3.8.x before 3.8.3, and 3.9.x before 3.9.1 fail to properly remove sshd_lock files from /tmp/ after SSHv1 connections terminate. Remote attackers can exploit this by initiating many SSHv1 connections, causing accumulation of lock files that consume disk space and lead to denial of service.

MitigationUpgrade Cisco IOS XR to version 3.8.3, 3.9.1, or later. As a workaround, implement periodic cleanup of /tmp/sshd_lock files via scheduled task or monitoring to prevent disk exhaustion.

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:= 3.6.0= 3.6.1= 3.6.2= 3.6.3= 3.8.0= 3.8.1= 3.8.2= 3.9.0

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 IOS XR version
    Run 'show version' or 'admin show version' to retrieve the installed Cisco IOS XR version
    Affected if Version matches 3.6.0-3.6.3, 3.8.0-3.8.2, or 3.9.0 (the affected versions listed)
  2. Check for accumulated lock files
    Run 'ls -la /tmp/sshd_lock*' or 'dir /tmp/sshd_lock*' to list any sshd_lock files in /tmp
    Affected if Multiple sshd_lock files are present in /tmp, indicating the cleanup failure is occurring
  3. Verify SSHv1 is enabled
    Run 'show ssh server' or check the SSH configuration to see if SSH Protocol Version 1 is enabled
    Affected if SSHv1 is enabled, as the vulnerability specifically affects SSHv1 connections

You are affected if running a listed affected version (3.6.0-3.6.3, 3.8.0-3.8.2, or 3.9.0) and SSHv1 is enabled with accumulated /tmp/sshd_lock files present on the system.

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 XR to version 3.8.3, 3.9.1, or later. As a workaround, implement periodic cleanup of /tmp/sshd_lock files via scheduled task or monitoring to prevent disk exhaustion.

Fix this in Ios Xr Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
18.0 hours of engineering $3,200
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Scan for this in your stack

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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-2011-0949 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