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Adaptive Security Appliance SoftwareOperating system · Cisco

CVE-2026-20039

HIGH · 8.6 CVSS v3.1 Published 2026-03-04
Fix available
A fix is available. Upgrade to 7.0.9 / 7.2.10 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 the VPN web server of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to ineffective memory management of the VPN web server. An attacker could exploit this vulnerability by sending a large number of crafted HTTP requests to an affected device. A successful exploit could allow the attacker to cause the device to reload, resulting in a DoS condition.

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

A memory management vulnerability in the VPN web server of Cisco ASA and FTD software allows unauthenticated remote attackers to trigger device reloads by sending crafted HTTP requests, causing denial of service.

MitigationApply Cisco security updates for ASA/FTD software; as an interim measure, restrict VPN web server access to trusted networks or implement rate limiting on the affected interface.

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
Adaptive Security Appliance SoftwareOperating system
Affected:>= 9.12.1, < 9.16.4.84>= 9.17.1, < 9.18.4.57>= 9.19.1, < 9.20.3.16>= 9.22.1.1, < 9.22.2.4>= 9.23.1, < 9.23.1.3
Secure Firewall Threat DefenseApplication
Affected:>= 6.4.0, < 7.0.9>= 7.1.0, < 7.2.10>= 7.3.0, < 7.4.3>= 7.6.0, < 7.6.1>= 7.7.0, < 7.7.10

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 product type and version
    Run 'show version' or 'show version | include (ASA|Firepower)' to determine if the device is Cisco ASA or Firepower Threat Defense and note the exact software version number.
    Affected if The device runs Cisco ASA Software version 9.12.1 to 9.16.4.83, 9.17.1 to 9.18.4.56, 9.19.1 to 9.20.3.15, 9.22.1.1 to 9.22.2.3, or 9.23.1 to 9.23.1.2; OR runs Cisco FTD Software version 6.4.0 to 7.0.8, 7.1.0 to 7.2.9, 7.3.0 to 7.4.2, 7.6.0, or 7.7.0 to 7.7.9.
  2. Confirm VPN web server is enabled
    Run 'show run webvpn' or 'show webvpn' to check if WebVPN (webvpn) feature is configured and active on the device.
    Affected if WebVPN is enabled and configured on the device.
  3. Identify VPN web server interface binding
    Run 'show run webvpn' and check for 'interface' statements under webvpn configuration to determine which interface the VPN web server is listening on (typically the outside or external interface).
    Affected if The VPN web server is bound to an external or untrusted interface accessible from the internet.
  4. Check external access control on VPN interface
    Run 'show run access-list' and inspect any access lists applied to the interface where webvpn is bound. Look for rules permitting HTTP/HTTPS from untrusted sources.
    Affected if There are no access lists or rate-limiting configured to restrict HTTP/HTTPS access to the VPN web server interface from external networks.

You are affected if your Cisco ASA or FTD device runs a vulnerable software version AND has WebVPN enabled on an externally accessible interface without adequate access controls.

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.

dbcve · scoped
Upgrade available Upgrade to 7.0.9 / 7.2.10 / 7.4.3 or later
Fixed in 7.0.97.2.107.4.3
Interim mitigation

Apply Cisco security updates for ASA/FTD software; as an interim measure, restrict VPN web server access to trusted networks or implement rate limiting on the affected interface.

Recommended fix Moderate confidence

ASA: 9.16.4.84, 9.18.4.57, 9.20.3.16, or 9.22.2.4 (depending on your release train); FTD: 7.0.9, 7.2.10, 7.4.3, or 7.6.1 (depending on your release train)

  1. 1. Identify the current version of Cisco ASA or FTD software running on the device using 'show version' command
  2. 2. For ASA Software: If running >= 9.12.1 and < 9.16.4.84, upgrade to 9.16.4.84 or later; or if running >= 9.17.1 and < 9.18.4.57, upgrade to 9.18.4.57 or later; or if running >= 9.19.1 and < 9.20.3.16, upgrade to 9.20.3.16 or later; or if running >= 9.22.1.1 and < 9.22.2.4, upgrade to 9.22.2.4 or later
  3. 3. For FTD Software: If running >= 6.4.0 and < 7.0.9, upgrade to 7.0.9 or later; or if running >= 7.1.0 and < 7.2.10, upgrade to 7.2.10 or later; or if running >= 7.3.0 and < 7.4.3, upgrade to 7.4.3 or later; or if running >= 7.6.0 and < 7.6.1, upgrade to 7.6.1 or later
  4. 4. Download the appropriate software from Cisco's download center at sec.cloudapps.cisco.com or via your Cisco smart account
  5. 5. Upload the new software to the device and follow standard Cisco upgrade procedures
  6. 6. Verify the upgrade was successful and the device is functioning normally
  7. 7. Test VPN functionality to ensure the vulnerability is remediated
Caveat Review Cisco release notes for any compatibility concerns or configuration changes before upgrading

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Adaptive Security Appliance Software Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA2.0 h
15.0 hours of engineering $2,580
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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-2026-20039 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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