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RouterHardware / appliance · Cisco

CVE-1999-0453

MEDIUM · 5.0 CVSS v2.0 Published 1999-01-01
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
An attacker can identify a CISCO device by sending a SYN packet to port 1999, which is for the Cisco Discovery Protocol (CDP).

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

An attacker can perform device fingerprinting by sending a SYN packet to TCP port 1999, which responds and reveals that the target is a Cisco device. This information disclosure enables reconnaissance and helps attackers identify potential Cisco infrastructure for further exploitation.

MitigationBlock port 1999 at the network perimeter firewall or disable Cisco Discovery Protocol (CDP) on untrusted network interfaces to prevent device identification.

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
RouterHardware / appliance
Affected:all versions

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. Verify if TCP port 1999 is listening
    Run 'show ip sockets' or 'show tcp brief' on the Cisco device to see if any service is bound to port 1999
    Affected if Port 1999 shows as listening or established in the output
  2. Test external response on port 1999
    From an external host, send a SYN packet to port 1999 of the Cisco device (e.g., using nmap -sS -p 1999 <device-ip>)
    Affected if The port responds with a SYN-ACK, revealing the device accepts connections on port 1999
  3. Check inbound access control lists
    Review all inbound ACLs on external-facing interfaces with 'show ip access-lists' and search for any permit statements allowing TCP port 1999
    Affected if An ACL permits traffic to port 1999 on any externally-facing interface
  4. Verify firewall or port filtering configuration
    Check if any interface-level traffic filters or zone-based firewall policies allow port 1999 traffic with 'show running-config | include access-list' or similar filtering commands
    Affected if No filter exists to block port 1999, or an explicit permit for port 1999 is found

The environment is affected if TCP port 1999 is accessible from untrusted networks and responds to connection attempts, revealing the device as Cisco infrastructure.

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

Block port 1999 at the network perimeter firewall or disable Cisco Discovery Protocol (CDP) on untrusted network interfaces to prevent device identification.

Fix this in Router Scoped from the published advisory
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing1.0 h
  • Review / QA1.0 h
5.0 hours of engineering $890
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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-1999-0453 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
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data