Server-Side Template Injection in SecureTransport's Apache Velocity mail templates

A Server-Side Template Injection (SSTI) vulnerability was identified in the mail template functionality of the Axway SecureTransport product in version 5.5-20260326. This flaw allows an attacker with admin privileges to inject arbitrary Java code expressions, which are executed server-side when the template is rendered (i.e., during email sending). Successful exploitation of this flaw allows an attacker to execute arbitrary code on the server that results in full host compromise. This issue affects all Axway SecureTransport versions prior 5.5-20260528 update.