A flaw was found in the way samba implemented an RPC endpoint emulating the Windows registry service API. An unprivileged attacker could use this flaw to create a new registry hive file anywhere they have unix permissions which could lead to creation of a new file in the Samba share.
As per samba upstream advisory:
Samba contains an RPC endpoint emulating the Windows registry service API. One of the requests, "winreg_SaveKey", is susceptible to a path/symlink traversal vulnerability. Unprivileged users can use it to create a new registry hive file anywhere they have unix permissions to create a new file within a Samba share. If they are able to create symlinks on a Samba share, they can create a new registry hive file anywhere they have write access, even outside a Samba share definition.
Note - existing share restrictions such as "read only" or share ACLs do *not* prevent new registry hive files being written to the filesystem. A file may be written under any share definition wherever the user has unix permissions to create a file.
Existing files cannot be overwritten using this vulnerability, only new registry hive files can be created, however the presence of existing files with a specific name can be detected.
Samba writes or detects the file as the authenticated user, not as root.
Name: Michael Hanselmann
openshift-online-3 does not provision samba endpoints.
This affects not only Linux <> Windows configurations but may also affect Linux <> Linux configurations using Samba as RPC endpoints. (since winreg_SaveKey RPC call is also implemented on the client side)
Either turn off SMB1 by setting the global parameter:
'min protocol = SMB2'
or if SMB1 is required turn off unix extensions by setting the global parameter:
'unix extensions = no'
in the smb.conf file.
Created samba tracking bugs for this issue:
Affects: fedora-all [bug 1697717]
This issue affects the version of samba shipped with Red Hat Gluster Storage 3, as it contains the vulnerable functionality.