CVE-2024-20353
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.
- CVSS
- 8.6Highscored by the publisher (CNA)
- Exploited in the wild
- Yes, in CISA KEV since 24 Apr 2024CISA deadline for US federal agencies: 1 May 2024
- EPSS
- 69.8%chance of exploitation in the next 30 daystop 0.7% of scored CVEsFIRST score of 11 Nov 2026
- Fix
- Patch availablesee the advisories in the references
- Published
- 24 Apr 2024analysed here 12 Nov 2026
Do first. Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable. (CISA's required action for this KEV entry)
Summary
Triage
- Exploitable
- At runtime
- Attack vector
- network
- Weakness
- CWE-835 Common Weakness
The summary, impact and action text on this page are written by our AI analysis pipeline, or taken from the NVD description when a CVE was imported from NVD. They are not the vendor's wording: check them against the sources. A longer AI executive summary and technical analysis are generated for signed-in accounts on the Max plan.
Affected products
| Product | Affected versions | Vendor says fixed in |
|---|---|---|
| Cisco Cisco Adaptive Security Appliance (ASA) Software | 9.8.19.8.1.59.8.1.79.8.29.8.2.89.8.2.149.8.2.159.8.2.179.8.2.209.8.2.249.8.2.269.8.2.289.8.2.339.8.2.359.8.2.389.8.3.89.8.3.119.8.3.149.8.3.169.8.3.189.8.3.219.8.39.8.3.269.8.3.299.8.49.8.4.39.8.4.79.8.4.89.8.4.109.8.4.129.8.4.159.8.4.179.8.4.259.8.4.209.8.4.229.8.4.269.8.4.299.8.4.329.8.4.339.8.4.349.8.4.359.8.4.399.8.4.409.8.4.419.8.4.439.8.4.449.8.4.459.8.4.469.8.4.489.12.19.12.1.29.12.1.39.12.29.12.2.49.12.2.59.12.2.99.12.39.12.3.29.12.3.79.12.49.12.3.129.12.3.99.12.2.19.12.4.29.12.4.49.12.4.79.12.4.109.12.4.139.12.4.89.12.4.189.12.4.249.12.4.269.12.4.299.12.4.309.12.4.359.12.4.379.12.4.389.12.4.399.12.4.409.12.4.419.12.4.479.12.4.489.12.4.509.12.4.529.12.4.549.12.4.559.12.4.569.12.4.589.12.4.629.12.4.659.14.19.14.1.109.14.1.69.14.1.159.14.1.199.14.1.309.14.29.14.2.49.14.2.89.14.2.139.14.2.159.14.39.14.3.19.14.3.99.14.3.119.14.3.139.14.3.189.14.3.159.14.49.14.4.69.14.4.79.14.4.129.14.4.139.14.4.149.14.4.159.14.4.179.14.4.229.14.4.239.15.19.15.1.79.15.1.109.15.1.159.15.1.169.15.1.179.15.1.19.15.1.219.16.19.16.1.289.16.29.16.2.39.16.2.79.16.2.119.16.2.139.16.2.149.16.39.16.3.39.16.3.149.16.3.159.16.3.199.16.3.239.16.49.16.4.99.16.4.149.16.4.189.16.4.199.16.4.279.16.4.389.16.4.399.16.4.429.16.4.489.16.4.559.17.19.17.1.79.17.1.99.17.1.109.17.1.119.17.1.139.17.1.159.17.1.209.17.1.309.17.1.339.18.19.18.1.39.18.29.18.2.59.18.2.79.18.2.89.18.39.18.3.399.18.3.469.18.3.539.18.3.559.18.3.569.18.49.18.4.59.18.4.89.19.19.19.1.59.19.1.99.19.1.129.19.1.189.19.1.229.19.1.249.19.1.279.20.19.20.1.59.20.2Vendor says fixed in: not stated | |
| Cisco Cisco Firepower Threat Defense Software | 6.2.36.2.3.16.2.3.26.2.3.36.2.3.46.2.3.56.2.3.66.2.3.76.2.3.86.2.3.106.2.3.116.2.3.96.2.3.126.2.3.136.2.3.146.2.3.156.2.3.166.2.3.176.2.3.186.6.06.6.0.16.6.16.6.36.6.46.6.56.6.5.16.6.5.26.6.76.6.7.16.4.06.4.0.16.4.0.36.4.0.26.4.0.46.4.0.56.4.0.66.4.0.76.4.0.86.4.0.96.4.0.106.4.0.116.4.0.126.4.0.136.4.0.146.4.0.156.4.0.166.4.0.176.7.06.7.0.16.7.0.26.7.0.37.0.07.0.0.17.0.17.0.1.17.0.27.0.2.17.0.37.0.47.0.57.0.67.0.6.17.1.07.1.0.17.1.0.27.1.0.37.2.07.2.0.17.2.17.2.27.2.37.2.47.2.4.17.2.57.2.5.17.3.07.3.17.3.1.17.4.07.4.1Vendor says fixed in: not stated |
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.
Products named in our analysis
- cisco:adaptive_security_appliance_software
- cisco:secure_firewall_threat_defense
Fix and mitigation
WAF and other mitigations
Can a WAF block it? Partly. The attack is delivered via a crafted HTTP request header to the device's web server. A WAF could partially detect this by matching unusual or malformed HTTP headers that normal users do not send, but some legitimate requests might also have uncommon headers, so filtering is only partly reliable. A custom WAF rule can filter crafted HTTP header with malformed or unexpected content, but attackers can vary the request. No tracked WAF vendor has published a rule for this CVE yet.
What a custom rule would match: crafted HTTP header with malformed or unexpected content
Also consider: patch · custom WAF rule
Based on an AI reading of the CVE description, and no vendor rule found yet. We check Cloudflare, AWS, Google Cloud Armor and Azure; for Akamai, Imperva, Fastly, F5, ask your vendor.
Remediation steps (AI-written)
Step-by-step remediation is generated for accounts on the Max plan, for CVEs that match a technology in their stack. Add this technology to your stack to see the fix checklist.
Exploitation evidence
- CISA KEV catalog
- Listed since 24 Apr 2024.
- CISA due date
- 1 May 2024, the remediation deadline for US federal agencies
- CISA required action
- Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.
- Public exploit code
- None on record in Exploit-DB, Metasploit, Nuclei templates or PoC-in-GitHub.
- CISA SSVC
- exploitation active, automatable yes, technical impact partialAssessed by CISA 29 Apr 2024 (SSVC 2.0.3). Exploitation is none, poc (public proof of concept) or active.
Timeline
- 24 Apr 2024Added to CISA KEV (exploited in the wild)
- 24 Apr 2024Published1 day later
- 29 Apr 2024CISA SSVC assessment: exploitation active5 days later
- 1 May 2024CISA remediation due date (US federal agencies)1 day later
- 21 Oct 2025CVE record last updated539 days (about 1 year) later
- 12 Nov 2026Analysed by vulneraibility.com387 days (about 1 year) later
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
| Metric | Value | What it means |
|---|---|---|
| Attack vector | NetworkReachable over the internet or any routable network. | Reachable over the internet or any routable network. |
| Attack complexity | LowRepeatable attack, no special conditions. | Repeatable attack, no special conditions. |
| Privileges required | NoneThe attacker needs no prior access. | The attacker needs no prior access. |
| User interaction | NoneNo victim action needed. | No victim action needed. |
| Scope | ChangedImpact crosses a security boundary into other components. | Impact crosses a security boundary into other components. |
| Confidentiality | NoneNo data disclosure. | No data disclosure. |
| Integrity | NoneNo unauthorised modification. | No unauthorised modification. |
| Availability | HighFull outage possible. | Full outage possible. |
Common questions
Is CVE-2024-20353 being exploited?
Yes. CVE-2024-20353 appears in CISA's Known Exploited Vulnerabilities catalog, which means exploitation in the wild has been confirmed and reported. Treat it as active rather than theoretical, and patch it ahead of higher-scoring vulnerabilities that carry no exploitation evidence.
How severe is CVE-2024-20353?
CVE-2024-20353 is rated High with a CVSS score of 8.6. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2024-20353?
Yes. A fix has been recorded for CVE-2024-20353. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2024-20353 affect?
CVE-2024-20353 affects cisco:adaptive_security_appliance_software, cisco:secure_firewall_threat_defense. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
References
3 references in the CVE record, grouped by the tags the record gives them.
Exploits (1)
- blog.talosintelligence.com /arcanedoor-new-espionage-focused-campaign-found-targeting-perimeter-network-dev
Other links (2)
- sec.cloudapps.cisco.com /security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-websrvs-dos-X8gNu
- cisa.gov /known-exploited-vulnerabilities-catalog?field_cve=CVE-2024-20353
Where the data on this page comes from
- CVE List (CVE.org): description, affected versions, references; CVE Terms of Use
- NVD: CVSS and CPE data
- CISA KEV catalog: exploitation, date added, due date
- CISA Vulnrichment (ADP): SSVC decision points
- FIRST EPSS: exploit probability and percentile
Summary, impact and triage tags: written by our AI analysis pipeline from the sources above. Check them against the sources.
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