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iOSOperating system · Cisco

CVE-2019-12655

HIGH · 7.5 CVSS v3.1 Published 2019-09-25
Fix available
A fix is available. Upgrade to 16.3.8 / 16.11.1 or later.
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 FTP application layer gateway (ALG) functionality used by Network Address Translation (NAT), NAT IPv6 to IPv4 (NAT64), and the Zone-Based Policy Firewall (ZBFW) in Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause an affected device to reload. The vulnerability is due to a buffer overflow that occurs when an affected device inspects certain FTP traffic. An attacker could exploit this vulnerability by performing a specific FTP transfer through the device. A successful exploit could allow the attacker to cause the device to reload.

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

A buffer overflow vulnerability exists in the FTP Application Layer Gateway (ALG) functionality within Cisco IOS XE Software when inspecting FTP traffic. The flaw affects devices using NAT, NAT64, or Zone-Based Policy Firewall (ZBFW) features. An unauthenticated remote attacker can trigger the overflow by sending crafted FTP traffic through the affected device, causing it to reload.

MitigationApply the Cisco IOS XE security patch when available; alternatively, disable FTP ALG inspection or filter/block FTP traffic through the affected device as a temporary workaround until patching can be completed.

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:>= 3.16.8s, < 16.3.8>= 16.10.1, < 16.11.1= 16.6.4= 16.6.5= 16.9.1= 16.9.2

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

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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 IOS XE version
    Run 'show version' on the device CLI and locate the version string (for example, 16.6.4 or 16.9.1)
    Affected if The installed version matches one of the affected ranges: >= 3.16.8s and < 16.3.8, >= 16.10.1 and < 16.11.1, or exactly 16.6.4, 16.6.5, 16.9.1, or 16.9.2
  2. Verify if NAT is configured and active
    Run 'show running-config | include ip nat' or 'show ip nat translations' to check for NAT configuration
    Affected if NAT is enabled on the device (the vulnerability requires NAT, NAT64, or ZBFW to be in use)
  3. Verify if NAT64 is configured
    Run 'show running-config | include nat64' to check for NAT64 configuration
    Affected if NAT64 is enabled on the device
  4. Verify if Zone-Based Policy Firewall is configured
    Run 'show zone-pair' or 'show class-map type inspect' to check for ZBFW policies
    Affected if ZBFW policies are configured on the device
  5. Confirm FTP ALG inspection status
    Run 'show ip alg' or check ALG module status; FTP ALG is typically enabled automatically when NAT or ZBFW inspects FTP traffic
    Affected if FTP ALG inspection is active (automatically enabled when NAT or ZBFW processes FTP traffic)

The device is affected if it runs a vulnerable IOS XE version from the listed ranges AND has NAT, NAT64, or ZBFW enabled, with FTP traffic being inspected by those features.

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
Upgrade available Upgrade to 16.3.8 / 16.11.1 or later
Fixed in 16.3.816.11.1
Interim mitigation

Apply the Cisco IOS XE security patch when available; alternatively, disable FTP ALG inspection or filter/block FTP traffic through the affected device as a temporary workaround until patching can be completed.

Fix this in iOS Scoped from the published advisory
  • Consultation6.0 h
  • Implementation8.0 h
  • Testing8.0 h
  • Review / QA4.0 h
26.0 hours of engineering $4,560
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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-2019-12655 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