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Secure Firewall Threat DefenseApplication · Cisco

CVE-2020-3191

HIGH · 8.6 CVSS v3.1 Published 2020-05-06
Fix available
A fix is available. Upgrade to 6.2.3.16 / 6.3.0.6 or later.
See remediation →
95/100
Remediation priority · Urgent
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 DNS over IPv6 packet processing for Cisco Adaptive Security Appliance (ASA) Software and Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the device to unexpectedly reload, resulting in a denial of service (DoS) condition. The vulnerability is due to improper length validation of a field in an IPv6 DNS packet. An attacker could exploit this vulnerability by sending a crafted DNS query over IPv6, which traverses the affected device. An exploit could allow the attacker to cause the device to reload, resulting in a DoS condition. This vulnerability is specific to DNS over IPv6 traffic only.

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 vulnerability in Cisco ASA and FTD software's DNS over IPv6 packet processing allows unauthenticated remote attackers to cause device reloads (DoS) due to improper length validation of a field in IPv6 DNS packets. The attacker sends a crafted DNS query over IPv6 that traverses the affected device.

MitigationApply the relevant Cisco security patch for ASA and FTD software when available. Until patched, consider filtering or blocking DNS over IPv6 traffic if not operationally required, or implement rate-limiting on IPv6 DNS traffic as a temporary workaround.

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
Secure Firewall Threat DefenseApplication
Affected:>= 6.2.3, < 6.2.3.16>= 6.3.0, < 6.3.0.6>= 6.4.0, < 6.4.0.6
Asa 5505 FirmwareOperating system
Affected:= 9.4\(1\)= 96.4\(0.42\)
Asa 5510 FirmwareOperating system
Affected:= 9.4\(1\)= 96.4\(0.42\)
Asa 5512 X FirmwareOperating system
Affected:= 9.4\(1\)= 96.4\(0.42\)
Asa 5515 X FirmwareOperating system
Affected:= 9.4\(1\)= 96.4\(0.42\)
Asa 5520 FirmwareOperating system
Affected:= 9.4\(1\)= 96.4\(0.42\)
Asa 5525 X FirmwareOperating system
Affected:= 9.4\(1\)= 96.4\(0.42\)
Asa 5540 FirmwareOperating system
Affected:= 9.4\(1\)= 96.4\(0.42\)

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
Changed
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/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 device model and software type
    Run 'show version' or 'show inventory' to determine if the device is a Cisco ASA or Firepower Threat Defense (FTD) appliance
    Affected if Device is an ASA or FTD model listed in the affected products
  2. Determine installed software version
    Run 'show version' and locate the running software version number (e.g., 9.4(1), 6.2.3.x, 6.3.0.x, or 6.4.0.x)
    Affected if Version falls within the affected ranges: FTD 6.2.3 through 6.2.3.15, 6.3.0 through 6.3.0.5, or 6.4.0 through 6.4.0.5; ASA firmware 9.4(1) or 96.4(0.42)
  3. Verify IPv6 is enabled on the device
    Run 'show ipv6 interface' or check configuration for 'ipv6 enable' under each interface
    Affected if IPv6 is enabled on any interface, allowing DNS over IPv6 packets to be processed
  4. Confirm DNS inspection is active
    Run 'show service-policy' or examine the configuration for 'inspect dns' in policy maps
    Affected if DNS inspection is enabled and applied to traffic traversing the device

The device is affected if it runs a vulnerable ASA or FTD version AND has IPv6 enabled with DNS inspection configured, allowing IPv6 DNS packets to traverse the device.

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 6.2.3.16 / 6.3.0.6 / 6.4.0.6 or later
Fixed in 6.2.3.166.3.0.66.4.0.6
Interim mitigation

Apply the relevant Cisco security patch for ASA and FTD software when available. Until patched, consider filtering or blocking DNS over IPv6 traffic if not operationally required, or implement rate-limiting on IPv6 DNS traffic as a temporary workaround.

Fix this in Secure Firewall Threat Defense Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,240
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Scan for this in your stack

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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-2020-3191 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