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Adaptive Security ApplianceApplication · Cisco

CVE-2021-40118

HIGH · 7.5 CVSS v3.1 Published 2021-10-27
Fix available
A fix is available. Upgrade to 6.4.0.13 / 6.6.5 or later.
See remediation →
84/100
Remediation priority · High
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 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 confidence

A vulnerability in the web services interface of Cisco ASA and FTD software allows an unauthenticated remote attacker to cause a denial of service by sending specially crafted HTTPS requests. The improper input validation during HTTPS request parsing triggers a device reload.

MitigationApply the relevant Cisco security updates for ASA and FTD software. Until patched, restrict management interface access to trusted networks via ACLs or VPN.

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
Affected:< 9.8.4.40
Secure Firewall Threat DefenseApplication
Affected:< 6.4.0.13>= 6.5.0, < 6.6.5>= 6.7.0, < 6.7.0.3>= 7.0.0, < 7.0.1
Adaptive Security Appliance SoftwareOperating system
Affected:>= 9.9.0, < 9.12.4.29>= 9.13.0, < 9.14.3.9>= 9.15.0, < 9.15.1.17>= 9.16.0, < 9.16.2.3
Asa 5512 X FirmwareOperating system
Affected:= 009.012\(004.024\)= 009.015\(001\)= 009.015\(001.015\)= 009.015\(001.016\)= 009.016\(001\)
Asa 5505 FirmwareOperating system
Affected:= 009.012\(004.024\)= 009.015\(001\)= 009.015\(001.015\)= 009.015\(001.016\)= 009.016\(001\)
Asa 5515 X FirmwareOperating system
Affected:= 009.012\(004.024\)= 009.015\(001\)= 009.015\(001.015\)= 009.015\(001.016\)= 009.016\(001\)
Asa 5525 X FirmwareOperating system
Affected:= 009.012\(004.024\)= 009.015\(001\)= 009.015\(001.015\)= 009.015\(001.016\)= 009.016\(001\)
Asa 5545 X FirmwareOperating system
Affected:= 009.012\(004.024\)= 009.015\(001\)= 009.015\(001.015\)= 009.015\(001.016\)= 009.016\(001\)

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
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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify device model and type
    Run 'show version' or 'show inventory' on the ASA/FTD device CLI to confirm the hardware model and software type (ASA or FTD)
    Affected if Device is not a Cisco ASA or Firepower Threat Defense appliance
  2. Check the software version
    Run 'show version' and look for the 'Software Version' line. For FTD, you may need to check via 'show version' in FTD CLI or the FMC interface
    Affected if Version falls within any of these ranges: ASA < 9.8.4.40; ASA 9.9.0 to < 9.12.4.29; ASA 9.13.0 to < 9.14.3.9; ASA 9.15.0 to < 9.15.1.17; ASA 9.16.0 to < 9.16.2.3; FTD < 6.4.0.13; FTD 6.5.0 to < 6.6.5; FTD 6.7.0 to < 6.7.0.3; FTD 7.0.0 to < 7.0.1; or if the specific firmware versions listed for ASA 5
  3. Verify HTTPS web services interface is enabled
    Run 'show running-config http' to see if HTTP server is enabled. Run 'show running-config | include http server' to check HTTPS server configuration
    Affected if HTTP or HTTPS server is enabled and the management interface is accessible from the network where the attack would originate
  4. Check management interface access control
    Run 'show running-config http' and 'show access-list' to determine which IP addresses or networks can reach the web services interface
    Affected if The management HTTPS interface is exposed to untrusted networks or the internet without ACL restrictions
  5. Confirm vulnerability trigger condition
    This vulnerability is triggered by sending specially crafted HTTPS requests to the web services interface. If your device has HTTPS management enabled and is reachable, it could be exploited
    Affected if Both the software version is in the affected range AND the HTTPS web services interface is accessible

A user is affected if they are running a vulnerable Cisco ASA or FTD version AND the device HTTPS web services interface is enabled and reachable from the network where the attack would originate.

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 6.4.0.13 / 6.6.5 / 6.7.0.3 or later
Fixed in 6.4.0.136.6.56.7.0.3
Interim mitigation

Apply the relevant Cisco security updates for ASA and FTD software. Until patched, restrict management interface access to trusted networks via ACLs or VPN.

Recommended fix High confidence

Upgrade to the minimum fixed version for your product line: ASA 9.8.4.40+, ASA 9.12.4.29+, ASA 9.14.3.9+, ASA 9.15.1.17+, ASA 9.16.2.3+, FTD 6.4.0.13+, FTD 6.6.5+, FTD 6.7.0.3+, or FTD 7.0.1+

  1. 1. Identify the exact version of Cisco ASA Software or FTD currently running on the affected device using the 'show version' command
  2. 2. Based on the product type, determine the minimum fixed version required: For Adaptive Security Appliance (ASA) <9.8.4.40, upgrade to 9.8.4.40 or later; For ASA Software 9.9.x-9.12.x, upgrade to 9.12.4.29 or later; For ASA Software 9.13.x-9.14.x, upgrade to 9.14.3.9 or later; For ASA Software 9.15.x, upgrade to 9.15.1.17 or later; For ASA Software 9.16.x, upgrade to 9.16.2.3 or later; For FTD <6
  3. 3. Download the appropriate software image from Cisco's software download center (tools.cisco.com) using valid Cisco credentials
  4. 4. Upload the new software image to the device using the 'copy' command or through the device's web interface
  5. 5. Perform the upgrade using the 'install' command (for ASA) or 'upgrade' command (for FTD), or schedule via the device manager
  6. 6. After installation completes, verify the new version using 'show version' and confirm the device is functioning normally
  7. 7. Test that the web services interface responds correctly to HTTPS requests to verify the vulnerability is remediated
Caveat Review Cisco release notes for each target version for any compatibility caveats, feature changes, or upgrade path requirements—some upgrades may require intermediate steps

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
  • Implementation3.0 h
  • Testing2.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,820
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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-2021-40118 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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