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Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 1 May 2024.
Adaptive Security Appliance SoftwareOperating system · Cisco

CVE-2024-20353

HIGH · 8.6 CVSS v3.1 Published 2024-04-24
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
In the wild High EPSS Public exploit 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 management and VPN web servers for Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the device to reload unexpectedly, resulting in a denial of service (DoS) condition. This vulnerability is due to incomplete error checking when parsing an HTTP header. An attacker could exploit this vulnerability by sending a crafted HTTP request to a targeted web server on a device. A successful exploit could allow the attacker to cause a DoS condition when the device reloads.

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 vulnerability in the management and VPN web servers of Cisco ASA and FTD software allows unauthenticated remote attackers to trigger unexpected device reloads via crafted HTTP requests. The root cause is incomplete error checking during HTTP header parsing, leading to a denial of service when the malformed request is processed.

MitigationApply Cisco-provided patches or software updates for ASA and FTD. If immediate patching is not possible, consider restricting access to management and VPN web servers via ACLs to reduce attack surface.

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:= 9.8.1= 9.8.1.5= 9.8.1.7= 9.8.2= 9.8.2.8= 9.8.2.14= 9.8.2.15= 9.8.2.17= 9.8.2.20= 9.8.2.24= 9.8.2.26= 9.8.2.28
Secure Firewall Threat DefenseApplication
Affected:= 6.2.3= 6.2.3.1= 6.2.3.2= 6.2.3.3= 6.2.3.4= 6.2.3.5= 6.2.3.6= 6.2.3.7= 6.2.3.8= 6.2.3.9= 6.2.3.10= 6.2.3.11

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
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 the Cisco product running
    Run 'show version' on the device CLI to determine if it is Cisco ASA or Cisco Firepower Threat Defense (FTD)
    Affected if The device is running Cisco ASA Software or Cisco Firepower Threat Defense
  2. Check the installed ASA version
    Run 'show version | include Version' in ASA CLI or check 'show version' output for the software version number
    Affected if The ASA version matches any of: 9.8.1, 9.8.1.5, 9.8.1.7, 9.8.2, 9.8.2.8, 9.8.2.14, 9.8.2.15, 9.8.2.17, 9.8.2.20, 9.8.2.24, 9.8.2.26, or 9.8.2.28
  3. Check the installed FTD version
    Run 'show version' in FTD CLI or check the device manager for the FTD software version
    Affected if The FTD version matches any of: 6.2.3, 6.2.3.1, 6.2.3.2, 6.2.3.3, 6.2.3.4, 6.2.3.5, 6.2.3.6, 6.2.3.7, 6.2.3.8, 6.2.3.9, 6.2.3.10, or 6.2.3.11
  4. Determine if the web management interface is accessible
    Check if the ASA/FTD web server is reachable by testing TCP port 443 or 80 on the device interface IP addresses
    Affected if The management or VPN web interface is exposed to network where attackers can send HTTP requests

The device is affected if it runs Cisco ASA Software version 9.8.1 through 9.8.2.28 (specific builds listed) or Cisco FTD version 6.2.3.x (specific builds listed) AND has the management or VPN web interface accessible to untrusted networks.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply Cisco-provided patches or software updates for ASA and FTD. If immediate patching is not possible, consider restricting access to management and VPN web servers via ACLs to reduce attack surface.

Recommended fix Moderate confidence

Contact Cisco TAC or check sec.cloudapps.cisco.com for the specific fixed release; Cisco typically addresses ASA vulnerabilities in subsequent 9.x releases and FTD in subsequent 6.x releases

  1. 1. Identify the exact Cisco ASA or FTD version currently installed using 'show version' command
  2. 2. Contact Cisco Technical Assistance Center (TAC) or check Cisco's Security Advisory portal at sec.cloudapps.cisco.com for the specific fixed release for your product version
  3. 3. Download the appropriate fixed software release from Cisco's Software Download center
  4. 4. Plan maintenance window as the device will need to be reloaded after software upgrade
  5. 5. Back up current configuration using 'write mem' or 'copy running-config startup-config'
  6. 6. Upgrade the device using the appropriate method (ASDM, CLI, or ROMMON for failsafe)
  7. 7. Verify the upgrade completed successfully with 'show version'
  8. 8. Confirm the vulnerability is remediated by checking the new version matches Cisco's fixed release
Caveat Review Cisco release notes for any compatibility or configuration changes between your current version and the fixed release; some upgrades may require ASDM version updates

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

Fix this in Adaptive Security Appliance Software Exploited in the wild — priority engagement
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA2.0 h
20.0 hours of engineering $3,500
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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-2024-20353 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
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data