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Ios XeOperating system · Cisco

CVE-2019-12664

HIGH · 7.5 CVSS v3.1 Published 2019-09-25
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
A vulnerability in the Dialer interface feature for ISDN connections in Cisco IOS XE Software for Cisco 4000 Series Integrated Services Routers (ISRs) could allow an unauthenticated, adjacent attacker to pass IPv4 traffic through an ISDN channel prior to successful PPP authentication. The vulnerability is due to insufficient validation of the state of the PPP IP Control Protocol (IPCP). An attacker could exploit this vulnerability by making an ISDN call to an affected device and sending traffic through the ISDN channel prior to successful PPP authentication. Alternatively, an unauthenticated, remote attacker could exploit this vulnerability by sending traffic through an affected device that is configured to exit via an ISDN connection for which both the Dialer interface and the Basic Rate Interface (BRI) have been configured, but the Challenge Handshake Authentication Protocol (CHAP) password for PPP does not match the remote end. A successful exploit could allow the attacker to pass IPv4 traffic through an unauthenticated ISDN connection for a few seconds, from initial ISDN call setup until PPP authentication fails.

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 confidence

This vulnerability in Cisco IOS XE Software's Dialer interface for ISDN connections allows an attacker to pass IPv4 traffic through an ISDN channel before PPP authentication completes. The flaw is due to insufficient validation of the PPP IPCP state, enabling traffic to traverse the connection during the authentication window of a few seconds.

MitigationApply the Cisco IOS XE software update that addresses this vulnerability. Additionally, ensure CHAP credentials are properly configured and consider disabling ISDN if not required, or implementing additional network segmentation controls around affected devices.

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
Ios XeOperating system
Affected:= 16.6.4

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
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/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 Cisco IOS XE version
    Run 'show version' or 'show running-config | include version' to determine the installed IOS XE version
    Affected if Version is 16.6.4 specifically (exact match)
  2. Verify ISDN interface configuration
    Run 'show running-config | include isdn' or 'show interface' to list ISDN-related interfaces on the device
    Affected if ISDN interfaces (BRI or PRI) are configured on the device
  3. Check Dialer interface configuration
    Run 'show running-config | include dialer' or 'show dialer interface' to examine Dialer interface settings used for ISDN
    Affected if Dialer interfaces are configured for ISDN connections
  4. Confirm PPP authentication settings
    Run 'show running-config interface [dialerX]' to inspect the PPP authentication configuration (CHAP or PAP) on the Dialer interface
    Affected if PPP authentication (CHAP or PAP) is configured on the Dialer interface and IPCP is enabled (via 'ip address negotiated' or static IPCP configuration)
  5. Review PPP IPCP negotiation timing
    Examine the Dialer interface configuration for 'ppp ipcp fast-start' or similar settings that may allow IPCP negotiation before authentication completes
    Affected if IPC P negotiation is set to 'fast-start' or similar timing that permits traffic before authentication phase concludes

A device is affected if it runs Cisco IOS XE version 16.6.4 exactly and has ISDN Dialer interfaces configured with PPP authentication, allowing IPCP to complete before authentication finishes.

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

Apply the Cisco IOS XE software update that addresses this vulnerability. Additionally, ensure CHAP credentials are properly configured and consider disabling ISDN if not required, or implementing additional network segmentation controls around affected devices.

Fix this in Ios Xe Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing4.0 h
  • Review / QA2.0 h
15.0 hours of engineering $2,640
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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-2019-12664 in production — separate from our analysis above.

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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
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  • Version or environment caveats, and links to real fixes
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