Zimbra Collaboration Suite: Missing authorization in ConfigureZimletRequest (CVE-2026-93639)

A missing authorization vulnerability in Zimbra Collaboration Suite (ZCS) allows a delegated administrator with no explicit administrative grants to overwrite global Zimlet configuration through ConfigureZimletRequest. This allows an attacker to add an attacker-controlled domain to the proxy allowlist. If a signed-in user opens a crafted /service/proxy URL, Zimbra serves attacker-controlled HTML under its own origin. The resulting JavaScript can read mailbox data and perform authenticated actions as the victim. Exploitation requires a delegated-administrator account and access to the admin SOAP service; the browser compromise requires the victim to open the crafted URL. ZCS 10.1.16 and 10.1.20 are affected.