Adaptive Security ApplianceApplication · Cisco
CVE-2021-1573
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 web services interface of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to trigger a denial of service (DoS) condition. This vulnerability is due to improper input validation when parsing HTTPS requests. An attacker could exploit this vulnerability by sending a malicious HTTPS request 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 · high confidenceThe vulnerability exists in the web services interface of Cisco ASA and FTD Software due to improper input validation during HTTPS request parsing. An unauthenticated remote attacker can send specially crafted malicious HTTPS requests that trigger a device reload, causing 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 ApplianceApplication
<= 9.7
Secure Firewall Threat DefenseApplication
<= 6.2.2>= 6.2.3, < 6.4.0.13>= 6.5.0, < 6.6.5>= 6.7.0, < 6.7.0.3= 7.0.0
Adaptive Security Appliance SoftwareOperating system
>= 9.8, < 9.8.4.40>= 9.9, < 9.12.4.26>= 9.13, < 9.14.3>= 9.15, < 9.15.1.17>= 9.16, < 9.16.1.28CVSS 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
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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.
-
Identify the product typeLog into the device CLI and run `show version` to determine if the device is running Cisco Adaptive Security Appliance (ASA) or Cisco Firepower Threat Defense (FTD). Look for the software name in the output.Affected if The device is either Cisco ASA or Cisco FTD
-
Determine the ASA software versionIf the device is ASA, run `show version` and locate the version string (for example, it may show 'Version 9.8(4)40' or similar). Compare your version number against the affected ranges: <= 9.7, >= 9.8 and < 9.8.4.40, >= 9.9 and < 9.12.4.26, >= 9.13 and < 9.14.3, >= 9.15 and < 9.15.1.17, or >= 9.16 and < 9.16.1.28.Affected if Your ASA version falls into any of the affected version ranges listed above
-
Determine the FTD software versionIf the device is FTD, run `show version` and locate the FTD version number (for example, it may show 'Version 6.4.0.13'). Compare your version against the affected ranges: <= 6.2.2, >= 6.2.3 and < 6.4.0.13, >= 6.5.0 and < 6.6.5, >= 6.7.0 and < 6.7.0.3, or = 7.0.0.Affected if Your FTD version matches any of the affected version ranges listed above
-
Verify web services interface exposureRun `show running-config | include http` or `show running-config | include management` to check if the HTTPS management interface is enabled and accessible. Also check access lists with `show access-list` to see if external networks are permitted to reach the web services interface.Affected if The HTTPS management interface (web services) is enabled and accessible from untrusted networks (not limited to localhost or management-only VLANs)
A device is affected if it runs a vulnerable ASA or FTD version AND has the web services interface exposed to network traffic from untrusted sources.
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 · scoped6.4.0.136.6.56.7.0.3
Apply the Cisco software updates for ASA and FTD that address this vulnerability. If patches are unavailable, consider restricting web services interface access to trusted networks or using access lists to limit exposure.
Upgrade to the minimum fixed version for your product line (ASA: 9.8.4.40/9.12.4.26/9.14.3/9.15.1.17 or later; FTD: 6.4.0.13/6.6.5/6.7.0.3 or later). For ASA 9.15.x, upgrade to 9.15.1.17 or later. For FTD 6.7.0, upgrade to 6.7.0.3 or later.
- 1. Identify the current Cisco ASA or FTD software version using 'show version' command
- 2. Based on current version, determine the minimum fixed release needed from: ASA 9.8.4.40+, 9.12.4.26+, 9.14.3+, or 9.15.1.17+; FTD 6.4.0.13+, 6.6.5+, or 6.7.0.3+
- 3. Download the appropriate fixed software image from Cisco (requires valid Cisco service contract)
- 4. Transfer the new image to the device using 'copy' command or through the device management interface
- 5. Install the upgrade using 'install' command (for ASA) or via FMC/FP appliance for FTD
- 6. Verify the upgrade was successful and the device is operational with 'show version'
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Adaptive Security Appliance
Scoped from the published advisory
- Consultation4.0 h
- Implementation4.0 h
- Testing4.0 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 $3,968.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-1573 — 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-2021-1573 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
Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.
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.
- 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