{"id":"CVE-2021-1402","title":"A vulnerability in the software-based SSL/TLS message handler of Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to trigger a reload of an affected device, resulting in a denial of service (D…","summary":"A vulnerability in the software-based SSL/TLS message handler of Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to trigger a reload of an affected device, resulting in a denial of service (D…","severity":"high","cvss":8.6,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H","cwe":["CWE-119","CWE-20"],"vendor":"cisco","product":"secure_firewall_threat_defense","affected":["secure_firewall_threat_defense >= 6.3.0, < 6.4.0","secure_firewall_threat_defense >= 6.5.0, < 6.6.0"],"patched":["secure_firewall_threat_defense 6.6.0"],"published":"2021-04-29","updated":"2026-08-11","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2021-1402","references":[{"url":"https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-ssl-decrypt-dos-DdyLuK6c","label":"psirt@cisco.com"},{"url":"https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-ssl-decrypt-dos-DdyLuK6c","label":"af854a3a-2127-422b-91ae-364da2661108"}],"tags":["nvd"],"epss":0.01386,"epssPercentile":0.70605,"ingestedAt":"2026-08-18T12:28:06.951Z","slug":"CVE-2021-1402","body":"## Overview\n\nA vulnerability in the software-based SSL/TLS message handler of Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to trigger a reload of an affected device, resulting in a denial of service (DoS) condition. The vulnerability is due to insufficient validation of SSL/TLS messages when the device performs software-based SSL decryption. An attacker could exploit this vulnerability by sending a crafted SSL/TLS message through an affected device. SSL/TLS messages sent to an affected device do not trigger this vulnerability. A successful exploit could allow the attacker to cause a process to crash. This crash would then trigger a reload of the device. No manual intervention is needed to recover the device after the reload.\n\n## Affected\n\n- `secure_firewall_threat_defense >= 6.3.0, < 6.4.0`\n- `secure_firewall_threat_defense >= 6.5.0, < 6.6.0`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `secure_firewall_threat_defense 6.6.0`","depth":"twilight","depthScore":48,"depthScoreParts":{"impact":47.3,"likelihood":0.3,"exploitation":0,"ransomware":0},"changes":[]}