As per upstream:
Samba client code always requests a forwardable ticket when using Kerberos authentication. This means the target server, which must be in the current or trusted domain/realm, is given a valid general purpose Kerberos "Ticket Granting Ticket" (TGT), which can be used to fully impersonate the authenticated user or service.
The risks of impersonation of the client are similar to the well known risks from forwarding of NTLM credentials, with two important differences: - NTLM forwarding can and should be mitigated with packet signing - Kerberos forwarding can only be attempted after the trusted destination server decrypts the ticket.
Finally, it should be noted that typically the connections involved are either explicitly requested, or are between or to Domain Controllers already of ultimate privilege.
The NTLMSSP authentication implementation in Samba 3.x and 4.x before 4.2.11, 4.3.x before 4.3.8, and 4.4.x before 4.4.2 allows man-in-the-middle attackers to perform protocol-downgrade attacks by modifying the client-server data stream to remove application-layer flags or encryption settings, as demonstrated by clearing the NTLMSSPNEGOTIATESEAL or NTLMSSPNEGOTIATESIGN option to disrupt LDAP security.
client/mount.cifs.c in mount.cifs in smbfs in Samba 3.4.5 and earlier does not verify that the (1) device name and (2) mountpoint strings are composed of valid characters, which allows local users to cause a denial of service (mtab corruption) via a crafted string.
Stack-based buffer overflow in the sendmailslot function in nmbd in Samba 3.0.0 through 3.0.27a, when the "domain logons" option is enabled, allows remote attackers to execute arbitrary code via a GETDC mailslot request composed of a long GETDC string following an offset username in a SAMLOGON logon request.
Stack-based buffer overflow in the replynetbiospacket function in nmbd/nmbdpackets.c in nmbd in Samba 3.0.0 through 3.0.26a, when operating as a WINS server, allows remote attackers to execute arbitrary code via crafted WINS Name Registration requests followed by a WINS Name Query request.
Stack-based buffer overflow in nmbd in Samba 3.0.0 through 3.0.26a, when configured as a Primary or Backup Domain controller, allows remote attackers to have an unknown impact via crafted GETDC mailslot requests, related to handling of GETDC logon server requests.
The Winbind nssinfo extension (nsswitch/idmapad.c) in idmapad.so in Samba 3.0.25 through 3.0.25c, when the "winbind nss info" option is set to rfc2307 or sfu, grants all local users the privileges of gid 0 when the (1) RFC2307 or (2) Services for UNIX (SFU) primary group attribute is not defined.
The RPC code generator in Samba 3.x before 3.4.16, 3.5.x before 3.5.14, and 3.6.x before 3.6.4 does not implement validation of an array length in a manner consistent with validation of array memory allocation, which allows remote attackers to execute arbitrary code via a crafted RPC call.
An integer overflow flaw was found in the way samba read an EA list provided by the client. A malicious client could send a specially crafted EA list that wraps perfectly on a 32-bit boundary, causing the server to loop and re-process the list. This can cause Denial of Service via memory exhaustion.
Reference:
https://bugzilla.samba.org/showbug.cgi?id=10010 (curently private)
It was found that samba before 4.4.16, 4.5.x before 4.5.14, and 4.6.x before 4.6.8 did not enforce "SMB signing" when certain configuration options were enabled. A remote attacker could launch a man-in-the-middle attack and retrieve information in plain-text.