Nx OsOperating system · Cisco
CVE-2013-1121
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 · uneditedThe regex engine in the BGP implementation in Cisco NX-OS, when a complex regular expression is configured for inbound routes, allows remote attackers to cause a denial of service (device reload) via a crafted AS path set, aka Bug ID CSCuf49554.
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 confidenceA denial of service vulnerability exists in the BGP regex engine of Cisco NX-OS. When a complex regular expression is configured for inbound route filtering, processing a crafted AS path set triggers the vulnerability, causing the device to reload unexpectedly.
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 OsOperating system
all versionsCVSS 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 checksWork through these to decide whether this CVE applies to you.
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Confirm Cisco NX-OS is runningUse 'show version' to identify the operating system and its versionAffected if The device runs any version of Cisco NX-OS
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Verify BGP is enabledCheck the configuration with 'show running-config | include router bgp' or 'show bgp process'Affected if BGP is configured and active on the device
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Identify AS path access-listsRun 'show ip as-path access-list' to list any AS path access-lists configuredAffected if Any AS path access-lists exist in the configuration
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Inspect route-maps for BGP regex matchingExamine route-maps with 'show route-map' and check for 'match as-path' clauses referencing AS path access-listsAffected if Route-maps use AS path matching for inbound route filtering
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Review regex complexity in AS path filtersExamine the regex patterns in the AS path access-lists identified, looking for complex constructs like nested groups, alternations, or extensive repetitionAffected if Complex regular expressions are configured in AS path filters used for inbound BGP route filtering
The device is affected if it runs Cisco NX-OS with BGP enabled and has complex AS path regex filters configured for inbound route filtering, as processing a crafted AS path set against these filters can trigger the reload.
Generated from the published advisory. Verify against your own configuration.
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 dataApply the relevant Cisco NX-OS patch for Bug ID CSCuf49554. Until patches are available, consider restricting BGP peer relationships to trusted sources and reviewing regex-based AS path filters for necessity and complexity.
Fix this in Nx Os
Scoped from the published advisory
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,600.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2013-1121 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2013-1121 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
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