dbcve.org
iOSOperating system · Cisco

CVE-1999-0161

HIGH · 7.5 CVSS v2.0 Published 1995-07-31
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
84/100
Remediation priority · High
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 IOS 10.3, with the tacacs-ds or tacacs keyword, an extended IP access control list could bypass filtering.

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

In Cisco IOS 10.3, the presence of the 'tacacs-ds' or 'tacacs' keyword in an extended IP access control list allows the ACL to bypass intended filtering, permitting unauthorized traffic to pass through security controls.

MitigationUpgrade from Cisco IOS 10.3 to a supported, patched version; for end-of-life IOS versions, consider replacing the legacy infrastructure with modern equipment.

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:= 10.3\(3.4\)= 10.3\(4.2\)

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
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 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 (e.g., 'Cisco IOS Software, Version 10.3(4.2)')
    Affected if The device runs Cisco IOS version 10.3, specifically versions 10.3(3.4) or 10.3(4.2)
  2. Confirm the exact IOS release
    Extract the full version string from the 'show version' output, noting both the main release (10.3) and the subrelease in parentheses
    Affected if The version shows exactly 10.3(3.4) or 10.3(4.2)
  3. Locate extended IP access control lists
    Run 'show ip access-lists' to list all configured IP access lists; identify any extended ACLs (those with entries starting with 'permit' or 'deny' and including protocol specifications like 'tcp', 'udp', 'icmp', or 'ip')
    Affected if Extended IP ACLs are configured on the device
  4. Inspect ACLs for vulnerable keywords
    Within each extended ACL, search for the keywords 'tacacs-ds' or 'tacacs' appearing in any ACL entry (typically as part of 'permit' or 'deny' statements with these keywords)
    Affected if Any extended IP ACL contains the 'tacacs-ds' or 'tacacs' keyword, which would trigger the bypass vulnerability

A device is affected if it runs Cisco IOS 10.3(3.4) or 10.3(4.2) AND has extended IP access control lists configured that include the 'tacacs-ds' or 'tacacs' keywords.

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 from Cisco IOS 10.3 to a supported, patched version; for end-of-life IOS versions, consider replacing the legacy infrastructure with modern equipment.

Fix this in iOS Scoped from the published advisory
  • Consultation12.0 h
  • Implementation24.0 h
  • Testing16.0 h
  • Review / QA8.0 h
60.0 hours of engineering $10,560
Get help mitigating

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $16,896.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-1999-0161 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-1999-0161 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

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
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data