Adaptive Security Appliance SoftwareOperating system · Cisco
CVE-2026-20082
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 · uneditedA vulnerability in the handling of the embryonic connection limits in Cisco Secure Firewall Adaptive Security Appliance (ASA) Software could allow an unauthenticated, remote attacker to cause incoming TCP SYN packets to be dropped incorrectly. This vulnerability is due to improper handling of new, incoming TCP connections that are destined to management or data interfaces when the device is under a TCP SYN flood attack. An attacker could exploit this vulnerability by sending a crafted stream of traffic to an affected device. A successful exploit could allow the attacker to prevent all incoming TCP connections to the device from being established, including remote management access, Remote Access VPN (RAVPN) connections, and all network protocols that are TCP-based. This results in a denial of service (DoS) condition for affected features.
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 confidenceA vulnerability in Cisco ASA Software's handling of embryonic (half-open) TCP connection limits allows an unauthenticated remote attacker to cause legitimate incoming TCP SYN packets to be incorrectly dropped during a SYN flood attack. This incorrectly triggers the embryonic connection limit threshold, causing all incoming TCP connections—including management access, Remote Access VPN, and TCP-based network protocols—to be blocked, resulting in a denial of service.
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
>= 9.20.4.14, < 9.20.4.19CVSS 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 checksWork through these to decide whether this CVE applies to you.
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Identify Cisco ASA deploymentLocate Cisco Adaptive Security Appliance devices in your network inventory or documentation. Check for ASA 5500-X series, ASAv, or Firepower ASA devices.Affected if Cisco ASA Software is not deployed in your environment, this CVE does not apply.
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Check ASA software versionConnect to the ASA CLI and run the command 'show version' to display the installed software version. Look for the version number in the output, typically displayed as 'Version 9.x.x'.Affected if The installed version is 9.20.4.14 through 9.20.4.18 (inclusive). Versions outside this range are not affected.
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Verify ASA is handling TCP connectionsConfirm the ASA is configured with interface(s) accepting TCP traffic. Check running configuration with 'show running-config' for active interface assignments and TCP-based services such as management access, Remote Access VPN, or TCP-based network protocols.Affected if The ASA must be actively processing incoming TCP connections for the embryonic connection limit flaw to be triggered during a SYN flood.
Your environment is affected if you run Cisco ASA Software versions 9.20.4.14 through 9.20.4.18 and the device accepts incoming TCP connections.
Generated from the published advisory. Verify against your own configuration.
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 · scoped9.20.4.19
Apply the Cisco security update for ASA Software that addresses the improper embryonic connection limit handling. Alternatively, implement SYN flood mitigation mechanisms (such as rate limiting, TCP interception, or SYN cookies) on upstream devices or enable ASA's built-in SYN flood protection features.
ASA Software 9.20.4.19 or later
- 1. Identify the current Cisco ASA software version by running 'show version' command
- 2. Confirm the current version is within the affected range: >= 9.20.4.14 and < 9.20.4.19
- 3. Schedule a maintenance window for the upgrade as this will require a device reload
- 4. Download the fixed ASA software version 9.20.4.19 or later from Cisco (requires valid CCO account)
- 5. Upload the new ASA software image to the device using 'copy tftp://' or other file transfer method
- 6. Configure the device to boot from the new image using 'boot system' command
- 7. Verify the boot system configuration with 'show bootvar'
- 8. Save the configuration with 'write memory'
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Adaptive Security Appliance Software
Scoped from the published advisory
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,600.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-20082 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-20082 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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