Open redirect in Umbraco CMS - CVE-2026-117553
Published: November 3, 2026
Vulnerability details
The vulnerability allows a remote attacker to take over a back-office account and, if the victim is an administrator, gain full control of the back-office and potentially execute code on the server.
The vulnerability exists due to insufficient validation of redirect destinations and inadequate handling of sign-in codes in the Umbraco CMS back-office sign-in flow when processing sign-in requests. A remote attacker can manipulate sign-in redirects and trick a signed-in back-office user into opening a crafted link to obtain an authenticated session with that user's privileges.
The full attack chain requires a web server or hosting setup that passes requests for unrecognised host names through to Umbraco.