Carrier Routing SystemApplication · Cisco
CVE-2012-1342
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 · uneditedCisco Carrier Routing System (CRS) 3.9, 4.0, and 4.1 allows remote attackers to bypass ACL entries via fragmented packets, aka Bug ID CSCtj10975.
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 confidenceCisco Carrier Routing System (CRS) versions 3.9, 4.0, and 4.1 contain an ACL bypass vulnerability where specially crafted fragmented packets can bypass configured Access Control List entries, potentially allowing unauthorized network access.
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
Carrier Routing SystemApplication
= 3.9.0= 4.0.0= 4.1.0CVSS 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
- Privileges
- None
- User interaction
- None
- Scope
- Changed
- Confidentiality
- None
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/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 checksWork through these to decide whether this CVE applies to you.
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Confirm Cisco CRS platformRun 'show version' or 'show hardware' to identify the system type. Look for 'Carrier Routing System' or 'CRS' in the output.Affected if The device is not a Cisco CRS platform (this CVE only affects CRS)
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Identify installed CRS versionExecute 'show version' and locate the software version number in the output. The version will appear as IOS XR release like 3.9.0, 4.0.0, or 4.1.0.Affected if The version equals exactly 3.9.0, 4.0.0, or 4.1.0
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Verify ACL configuration existsRun 'show access-lists' or 'show configuration access-list' to list any configured Access Control Lists.Affected if ACLs are configured on any interface (the bypass only matters if ACLs are in use)
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Inspect fragmented packet handlingReview ACL entries and test environment with fragmented packets matching blocked traffic to see if they bypass the ACL.Affected if Specially crafted fragments pass through when they should be denied by the configured ACL rules
You are affected if you run Cisco CRS versions 3.9.0, 4.0.0, or 4.1.0 AND have ACLs configured that could be bypassed by malicious fragmented packets.
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 Cisco software updates for CRS to patch this vulnerability; meanwhile, implement additional packet filtering at network boundaries to inspect and properly handle fragmented traffic until the vendor patch can be deployed.
Fix this in Carrier Routing System
Scoped from the published advisory
- Consultation6.0 h
- Implementation12.0 h
- Testing8.0 h
- Review / QA4.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $8,448.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2012-1342 — 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-2012-1342 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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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.
- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
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