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Nx OsApplication · Cisco

CVE-2011-2581

MEDIUM · 5.0 CVSS v2.0 Published 2011-09-14
Fix available
A fix is available. Upgrade to after 5.0 or later.
See remediation →
59/100
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
The ACL implementation in Cisco NX-OS 5.0(2) and 5.0(3) before 5.0(3)N2(1) on Nexus 5000 series switches, and NX-OS before 5.0(3)U1(2a) on Nexus 3000 series switches, does not properly handle comments in conjunction with deny statements, which allows remote attackers to bypass intended access restrictions in opportunistic circumstances by sending packets, aka Bug IDs CSCto09813 and CSCtr61490.

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

The ACL (Access Control List) implementation in Cisco NX-OS versions 5.0(2) and 5.0(3) on Nexus 5000 and 3000 series switches fails to properly parse comments when used in conjunction with deny statements. This parsing error causes the deny rules to be ineffective, allowing traffic that should be blocked to pass through the switch in certain configurations.

MitigationUpgrade NX-OS to version 5.0(3)N2(1) or later for Nexus 5000 series, or 5.0(3)U1(2a) or later for Nexus 3000 series. As a temporary workaround, avoid using comments within ACL configurations that contain deny statements until the firmware upgrade can be performed.

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
Nx OsApplication
Affected:= 5.0\(2\)= 5.0\(3\)n1\(1\)= 5.0\(3\)n1\(1a\)= 5.0\(3\)n1\(1b\)= 5.0\(3\)= 5.0\(3\)n1\(1c\)<= 5.0\(3\)u1\(2\)= 5.0\(3\)u1\(1a\)= 5.0\(3\)u1\(1b\)= 5.0\(3\)u1\(1d\)
Nexus 5000Hardware / appliance
Affected:all versions
Nexus 3000Hardware / appliance
Affected:all versions

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
Partial
Integrity
None
Availability
None

AV:N/AC:L/Au:N/C:P/I:N/A:N

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 NX-OS version
    Run 'show version' on the switch CLI to display the installed NX-OS version
    Affected if The version displayed is 5.0(2), 5.0(3), 5.0(3)n1(1), 5.0(3)n1(1a), 5.0(3)n1(1b), 5.0(3)n1(1c), 5.0(3)u1(1a), 5.0(3)u1(1b), 5.0(3)u1(1d), or any version 5.0(3)u1(2) or earlier
  2. Confirm hardware model
    Run 'show inventory' or 'show module' to identify the switch model
    Affected if The device is a Nexus 5000 series or Nexus 3000 series switch
  3. Review ACL configurations for comments
    Run 'show running-config | include "ip access-list|remark|!"' or 'show ip access-lists' to view ACL definitions. Examine each ACL for the presence of comment lines (remark statements or exclamation points) in the same access-list that contains deny statements
    Affected if An ACL contains both comment lines and deny statements in its configuration
  4. Verify ACL is actively applied
    Run 'show ip access-lists' to see applied ACLs, then run 'show running-config interface' for each interface to confirm where the ACL is bound (using 'ip access-group' in interface config)
    Affected if An ACL containing comments and deny statements is applied to one or more interfaces via 'ip access-group'

The environment is affected if the NX-OS version matches the listed affected versions, the hardware is a Nexus 5000 or 3000 series, and an ACL with both comments and deny statements is configured and actively applied to an interface.

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
Upgrade available Upgrade to a release after 5.0
Interim mitigation

Upgrade NX-OS to version 5.0(3)N2(1) or later for Nexus 5000 series, or 5.0(3)U1(2a) or later for Nexus 3000 series. As a temporary workaround, avoid using comments within ACL configurations that contain deny statements until the firmware upgrade can be performed.

Fix this in Nx Os Scoped from the published advisory
  • Consultation6.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA3.0 h
21.0 hours of engineering $3,780
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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-2011-2581 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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