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Adaptive Security Appliance SoftwareOperating system · Cisco

CVE-2026-20100

HIGH · 7.7 CVSS v3.1 Published 2026-03-04
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
83/100
Remediation priority · High
Remotely reachable 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 LUA interperter of the Remote Access SSL VPN feature of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Secure Firewall Threat Defense (FTD) Software could allow an authenticated, remote attacker with a valid VPN connection to cause the device to reload unexpectedly, resulting in a denial of service (DoS) condition. This does not affect the management or MUS interfaces. This vulnerability is due to trusting user input without validation in the LUA interprerter. An attacker could exploit this vulnerability by sending crafted HTTP packets to the Remote Access SSL VPN server. 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 · high confidence

A vulnerability in the LUA interpreter of the Remote Access SSL VPN in Cisco ASA and FTD software allows an authenticated remote attacker with a valid VPN connection to send crafted HTTP packets that cause the device to reload, resulting in denial of service. The root cause is improper validation of user input passed to the LUA interpreter.

MitigationApply the vendor patch when available. As a defensive measure, limit VPN user permissions and monitor for unexpected device reloads. Consider restricting VPN access to essential personnel until the patch is applied.

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= 9.12.1.2= 9.12.1.3= 9.12.2= 9.12.2.1= 9.12.2.4= 9.12.2.5= 9.12.2.9= 9.12.3= 9.12.3.2= 9.12.3.7= 9.12.3.9
Secure Firewall Threat DefenseApplication
Affected:= 6.4.0= 6.4.0.1= 6.4.0.2= 6.4.0.3= 6.4.0.4= 6.4.0.5= 6.4.0.6= 6.4.0.7= 6.4.0.8= 6.4.0.9= 6.4.0.10= 6.4.0.11

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
Low
User interaction
None
Scope
Changed
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:L/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 installed ASA software version
    Log into the ASA CLI and run 'show version' to display the running software version. For FTD, access through FMC or run 'show version' in FTD CLI.
    Affected if The version matches any of: 9.12.1, 9.12.1.2, 9.12.1.3, 9.12.2, 9.12.2.1, 9.12.2.4, 9.12.2.5, 9.12.2.9, 9.12.3, 9.12.3.2, 9.12.3.7, or 9.12.3.9
  2. Identify installed FTD software version
    Log into the Firepower Threat Defense CLI via SSH or console and run 'show version' to display the running software version.
    Affected if The version matches any of: 6.4.0, 6.4.0.1, 6.4.0.2, 6.4.0.3, 6.4.0.4, 6.4.0.5, 6.4.0.6, 6.4.0.7, 6.4.0.8, 6.4.0.9, 6.4.0.10, or 6.4.0.11
  3. Confirm Remote Access SSL VPN is enabled
    Run 'show vpn-sessiondb' or 'show run webvpn' in ASA CLI to check for active VPN sessions and webvpn configuration. For FTD, check via FMC or run 'show vpn-sessiondb' in FTD CLI.
    Affected if Remote Access SSL VPN (webvpn) is configured and active on the device
  4. Check for unexpected device reloads
    Run 'show crashinfo' or check system logs for recent reload events. Review 'show version' for last reload reason and timestamps.
    Affected if Device has reloaded unexpectedly or shows crash information without a known cause
  5. Review VPN user authentication logs
    Examine logs for VPN authentication events using 'show log' or syslogserver data. Look for authenticated VPN users sending HTTP traffic.
    Affected if There are authenticated VPN users whose sessions coincide with device reload events

You are affected if the device runs an affected ASA version (9.12.1 through 9.12.3.9) or FTD version (6.4.0 through 6.4.0.11) AND has Remote Access SSL VPN enabled, with the attack requiring an authenticated VPN user to send crafted HTTP packets.

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 vendor patch when available. As a defensive measure, limit VPN user permissions and monitor for unexpected device reloads. Consider restricting VPN access to essential personnel until the patch is applied.

Fix this in Adaptive Security Appliance Software Scoped from the published advisory
  • Consultation3.0 h
  • Implementation2.0 h
  • Testing4.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,920
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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-2026-20100 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
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