CVE-2018-15453: Cisco Email Security Appliance Memory Corruption Denial of Service Vulnerability

Security readout for executives and security teams

This flaw can let an unauthenticated remote sender disrupt a Cisco Email Security Appliance by sending a malformed S/MIME-signed email. If affected S/MIME features are enabled, the mail filtering process can repeatedly crash and restart, potentially causing sustained email security outage requiring manual recovery. Exposure is most likely on Cisco ESA deployments that process inbound or transit mail and have S/MIME Decryption and Verification or S/MIME Public Key Harvesting configured. The source bundle does not provide affected AsyncOS version ranges. Treat as high priority where Cisco ESA is business-critical for email security or mail delivery. The main risk is availability loss, not data theft, but sustained gateway disruption can affect inbound email, security filtering, and operational continuity. Mitigation focus: Check Cisco's advisory for supported update or workaround guidance.; Inventory Cisco ESA appliances and AsyncOS versions in production.; Disable affected S/MIME features if unused and operationally acceptable..

Prepared

May 23, 2026, 09:01 UTC (UTC+00:00)

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.