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iOSOperating system · Cisco

CVE-1999-0445

MEDIUM · 5.0 CVSS v2.0 Published 1999-04-01
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
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
In Cisco routers under some versions of IOS 12.0 running NAT, some packets may not be filtered by input access list filters.

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 · low confidence

In Cisco IOS 12.0 versions with NAT enabled, input access control lists fail to properly filter certain packets. This appears to be a packet filtering bypass where NAT processing may cause some traffic to circumvent input ACL inspection, potentially allowing unauthorized network access.

MitigationUpgrade to a patched IOS version beyond the affected 12.0 releases, and review ACL configurations when NAT is in use to ensure proper filtering. Consider additional filtering layers or zone-based policies as a compensating control.

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
iOSOperating system
Affected:= 12.0= 12.0\(1\)w= 12.0\(1\)xa3= 12.0\(1\)xb= 12.0\(1\)xe= 12.0\(2\)xc= 12.0\(2\)xd= 12.0\(2\)xf= 12.0\(2\)xg= 12.0db= 12.0s= 12.0t

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 the Cisco IOS version
    Run 'show version' on the device and locate the IOS release line (typically shows as something like '12.0(1)w' or '12.0s')
    Affected if The running IOS version exactly matches one of these: 12.0, 12.0(1)w, 12.0(1)xa3, 12.0(1)xb, 12.0(1)xe, 12.0(2)xc, 12.0(2)xd, 12.0(2)xf, 12.0(2)xg, 12.0db, 12.0s, or 12.0t
  2. Verify NAT is enabled
    Run 'show ip nat translations' or 'show ip nat statistics' to confirm NAT is configured and active
    Affected if NAT is actively translating packets or has active translations
  3. Confirm input ACLs are applied to NAT interfaces
    Run 'show ip interface' on each interface to check for 'Input access list' entries, or use 'show running-config | include access-group' to list all ACL bindings
    Affected if Input access lists (access-group in) are applied to interfaces where NAT is also configured
  4. Check the NAT and ACL configuration relationship
    Review the running-config to see if NAT and input ACLs are applied to the same interface(s)
    Affected if The device has NAT enabled on an interface that also has an input ACL applied for filtering

You are affected only if your device runs an exact 12.0.x version matching one of the listed releases AND has both NAT enabled AND input ACLs applied to NAT-configured interfaces simultaneously.

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 to a patched IOS version beyond the affected 12.0 releases, and review ACL configurations when NAT is in use to ensure proper filtering. Consider additional filtering layers or zone-based policies as a compensating control.

Fix this in iOS Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA2.0 h
20.0 hours of engineering $3,500
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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-1999-0445 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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