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A vulnerability in SSL/TLS message handler for Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability exists because incoming SSL/TLS packets are not properly processed. An attacker could exploit this vulnerability by sending a crafted SSL/TLS packet to an affected device. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a DoS condition.
Use CWE-119, Cisco vendor hub and Adaptive Security Appliance product page to widen CVE-2021-40117 into its surrounding weakness, vendor, and product context.
Compare it with CVE-2021-1573, CVE-2021-40118 and CVE-2021-34793 for nearby disclosures in the same product family. Additional editorial context is available in Cybersecurity Weekly Roundup: April 27, 2026 — Critical Zero-Days and Framework Failures.