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Cisco Email Security Appliance DNS Verification Denial of Service Vulnerability

A vulnerability in the DNS-based Authentication of Named Entities (DANE) email verification component of Cisco AsyncOS Software for Cisco Email Security Appliance (ESA) could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to insufficient error handling in DNS name resolution by the affected software. An attacker could exploit this vulnerability by sending specially formatted email messages that are processed by an affected device. A successful exploit could allow the attacker to cause the device to become unreachable from management interfaces or to process additional email messages for a period of time until the device recovers, resulting in a DoS condition. Continued attacks could cause the device to become completely unavailable, resulting in a persistent DoS condition. Cisco has released software updates that address this vulnerability. There are workarounds that address this vulnerability.