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Secure Firewall Threat DefenseApplication · Cisco

CVE-2020-3373

HIGH · 8.6 CVSS v3.1 Published 2020-10-21
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
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 the IP fragment-handling implementation of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a memory leak on an affected device. This memory leak could prevent traffic from being processed through the device, resulting in a denial of service (DoS) condition. The vulnerability is due to improper error handling when specific failures occur during IP fragment reassembly. An attacker could exploit this vulnerability by sending crafted, fragmented IP traffic to a targeted device. A successful exploit could allow the attacker to continuously consume memory on the affected device and eventually impact traffic, resulting in a DoS condition. The device could require a manual reboot to recover from the DoS condition. Note: This vulnerability applies to both IP Version 4 (IPv4) and IP Version 6 (IPv6) traffic.

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

Memory leak vulnerability in Cisco ASA/FTD IP fragment-handling implementation. Due to improper error handling during IP fragment reassembly, sending crafted fragmented IPv4/IPv6 packets allows an unauthenticated remote attacker to continuously consume memory until traffic processing fails, requiring manual reboot.

MitigationApply Cisco's security patches for this vulnerability; implement IP fragment reassembly limits or rate limiting as a compensating control until patches are deployed.

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:= 6.6.0.1
Adaptive Security Appliance SoftwareOperating system
Affected:= 9.8.4.22= 9.8.4.25= 9.12.4.2= 9.12.4.3= 9.13.1.12= 9.14.1.15

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 the Cisco device product type
    Log into the device CLI and run 'show version' or 'show inventory' to confirm whether the device is running Cisco Adaptive Security Appliance (ASA) or Cisco Firepower Threat Defense (FTD) software.
    Affected if The device runs ASA or FTD software.
  2. Check the installed ASA software version
    Run 'show version' and locate the version string (for example: 9.8.4.22, 9.12.4.2, 9.13.1.12, or 9.14.1.15). Compare this exact version to the list of affected versions.
    Affected if The ASA version matches exactly 9.8.4.22, 9.8.4.25, 9.12.4.2, 9.12.4.3, 9.13.1.12, or 9.14.1.15.
  3. Check the installed FTD software version
    Run 'show version' from the FTD CLI (or use FMC/ASDM) and locate the FTD version (for example: 6.6.0.1). Compare this exact version to the affected version.
    Affected if The FTD version matches exactly 6.6.0.1.
  4. Confirm IP fragment processing is enabled
    Verify the device is configured to process IPv4 and IPv6 traffic. This is the default state for ASA/FTD firewalls. Check with 'show run | include ip' or confirm the device has active IPv4/IPv6 interfaces and traffic flow.
    Affected if The device processes IPv4 or IPv6 traffic (default configuration for ASA/FTD).

You are affected if your device runs Cisco ASA software version 9.8.4.22, 9.8.4.25, 9.12.4.2, 9.12.4.3, 9.13.1.12, or 9.14.1.15, or Cisco FTD version 6.6.0.1, and the device is actively processing IPv4 or IPv6 traffic (which is the default state).

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 Cisco's security patches for this vulnerability; implement IP fragment reassembly limits or rate limiting as a compensating control until patches are deployed.

Fix this in Secure Firewall Threat Defense Scoped from the published advisory
  • Consultation4.0 h
  • Implementation6.0 h
  • Testing4.0 h
  • Review / QA2.0 h
16.0 hours of engineering $2,840
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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-2020-3373 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