12000 RouterHardware / appliance · Cisco
CVE-2001-0862
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 12000 with IOS 12.0 and line cards based on Engine 2 does not block non-initial packet fragments, which allows remote attackers to bypass the ACL.
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 confidenceThe Cisco 12000 series routers with IOS 12.0 and Engine 2 line cards fail to apply Access Control List (ACL) rules to non-initial IP packet fragments. Only the first fragment of a fragmented packet is checked against ACLs, while subsequent fragments are permitted regardless of the ACL rules, enabling attackers to bypass firewall restrictions by sending malicious payloads in fragment packets.
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
12000 RouterHardware / appliance
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
- Low
- Authentication
- None
- Confidentiality
- Partial
- Integrity
- Partial
- Availability
- Partial
AV:N/AC:L/Au:N/C:P/I:P/A:P
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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Identify the router modelUse the 'show version' or 'show hardware' command to confirm the device is a Cisco 12000 series routerAffected if The device is not a Cisco 12000 series router, then it is not affected by this specific CVE
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Check the IOS versionExecute 'show version' and look for the IOS version number in the 12.0 family (e.g., 12.0, 12.0S, 12.0ST, etc.)Affected if The IOS version is not in the 12.0 family, the device may not be affected by this specific vulnerability
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Verify Engine 2 line cards are presentUse 'show version' or 'show diag' to identify the line card engine types installed in the routerAffected if No Engine 2 line cards are present, the device is likely not affected by this vulnerability
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Check for configured ACLsUse 'show ip access-lists' to list all configured IP access control lists on the routerAffected if No ACLs are configured, the fragment bypass vulnerability cannot be exploited
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Verify ACL application to interfacesUse 'show ip interface' on relevant interfaces to confirm ACLs are applied to inbound or outbound trafficAffected if No ACLs are applied to any interface, the vulnerability cannot be exploited regardless of fragment handling
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Inspect fragment handling configurationReview ACL entries for 'fragments' keywords or use 'show running-config | include fragment' to check explicit fragment policiesAffected if ACLs lack explicit fragment handling rules (no 'fragment' keyword or 'deny fragment' statements), non-initial fragments can bypass the ACL filters
The environment is affected if it is a Cisco 12000 series router running IOS 12.0 with Engine 2 line cards and has ACLs applied to interfaces without explicit fragment handling rules.
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 dataUpgrade to a patched IOS version that properly filters all packet fragments and configure explicit fragment handling policies in ACLs.
Fix this in 12000 Router
Scoped from the published advisory
- Consultation3.0 h
- Implementation4.0 h
- Testing3.0 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 $3,408.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2001-0862 — 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-2001-0862 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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- Version or environment caveats, and links to real fixes
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