"rpcecho" development server allows Denial

Description

Samba developers have built a non-Windows RPC server known as
“rpcecho” to test elements of the Samba DCE/RPC stack under their full
control.

One RPC function provided by “rpcecho” can block, essentially
indefinitely, and because the “rpcecho” service is provided from the
main RPC task, which has only one worker, this denies essentially all
service on the AD DC.

To address this problem, the rpcecho server is removed from our
production binaries and is restricted to selftest builds only.

Patch Availability

Patches addressing both these issues have been posted to:

https://www.samba.org/samba/security/

Additionally, Samba 4.19.1, 4.18.8 and 4.17.12 have been issued
as security releases to correct the defect. Samba administrators are
advised to upgrade to these releases or apply the patch as soon
as possible.

CVSSv3 calculation

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H (6.5)

Workaround

Setting “dcerpc endpoint servers = -rpcecho” will disable the rpcecho
service on the AD DC.

Credits

Originally reported by Andrew Bartlett of Catalyst and the Samba Team.

Patches provided by Andrew Bartlett of Catalyst and the Samba Team.

Catalyst thanks Planet Innovation for supporting the production of
this security fix.

== Our Code, Our Bugs, Our Responsibility.
== The Samba Team