Yesterday, on April 12th, 2016, a new security bug named Badlock, has been disclosed.
The bug affects almost all current Samba releases.
Official site: http://badlock.org
Red Hat and CentOS already released the updates: https://access.redhat.com/security/vulnerabilities/badlock
Be aware that updating current NethServer installations could potentially lead to problems if Samba is configured in PDC mode and Windows workstations have joined the domain.
Actually all Windows machines joined to NethServer will not be able to login to the server after Samba update.
We are still investigating the issue, updates will be posted here, in the meanwhile we suggest not to update the Samba packages if you’re using NS as PDC.
Workaround 1: users who already updated the system, should downgrade all samba packages sign following command (edited, thanks to @maxbet):
yum downgrade samba* tdb-tools libtdb libtevent libtalloc pytalloc libldbWorkaround 2: use local cached credentials by disconnecting network cable from the Windows machine before login.