CVE-2019-14870

All Samba versions 4.x.x before 4.9.17, 4.10.x before 4.10.11 and 4.11.x before 4.11.3 have an issue, where the S4U (MS-SFU) Kerberos delegation model includes a feature allowing for a subset of clients to be opted out of constrained delegation in any way, either S4U2Self or regular Kerberos authentication, by forcing all tickets for these clients to be non-forwardable. In AD this is implemented by a user attribute delegation_not_allowed (aka not-delegated), which translates to disallow-forwardable. However the Samba AD DC does not do that for S4U2Self and does set the forwardable flag even if the impersonated client has the not-delegated flag set.

All Samba versions 4.x.x before 4.9.17, 4.10.x before 4.10.11 and 4.11.x before 4.11.3 have an issue, where the S4U (MS-SFU) Kerberos delegation model includes a feature allowing for a subset of clients to be opted out of constrained delegation in any way, either S4U2Self or regular Kerberos authentication, by forcing all tickets for these clients to be non-forwardable. In AD this is implemented by a user attribute delegation_not_allowed (aka not-delegated), which translates to disallow-forwardable. However the Samba AD DC does not do that for S4U2Self and does set the forwardable flag even if the impersonated client has the not-delegated flag set.

Todas las versiones de Samba 4.xx anteriores a 4.9.17, versiones 4.10.x anteriores a 4.10.11 y versiones 4.11.x anteriores a 4.11.3, presentan un problema, donde el modelo de delegación de Kerberos S4U (MS-SFU) incluye una funcionalidad que permite a un subconjunto de clientes ser excluidos de la delegación restringida de cualquier manera, ya sea S4U2Self o autenticación Kerberos regular, al forzar que todos los tickets para estos clientes no sean reenviables. En AD, esto es implementado mediante un atributo de usuario delegation_not_allowed (también se conoce como no delegado), que se traduce como no permitido-reenviable. Sin embargo, el AD DC Samba no hace eso para S4U2Self y establece el flag reenviable inclusive si el cliente suplantado tiene el conjunto de flags no delegados.