CVE-2018-15460: Cisco Email Security Appliance URL Filtering Denial of Service Vulnerability

Security readout for executives and security teams

Cisco ESA email filtering can be forced into a denial-of-service state by a remote unauthenticated sender. A malicious email containing many whitelisted URL references can drive CPU to 100%, potentially stopping the appliance from scanning and forwarding mail. The main business risk is email security gateway outage and mail-flow disruption, not data theft. Exposure is most likely where Cisco ESA appliances process inbound or outbound email with URL filtering and URL whitelist behavior enabled. The source bundle does not provide affected AsyncOS version details, so teams must verify appliance versions and configurations against Cisco's advisory. Prioritize this for organizations dependent on Cisco ESA for mail security or continuity. A successful attack can interrupt email delivery and security scanning without credentials. Treat as high operational risk, especially for internet-facing mail gateways. Mitigation focus: Review Cisco's advisory for affected AsyncOS versions and vendor-directed remediation.; Inventory Cisco ESA appliances and confirm whether URL filtering is enabled.; Apply Cisco-recommended fixed software or mitigations where applicable..

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.