Samba CVE-2016-2110: Man in the middle attacks possible with NTLMSSP

There are several man in the middle attacks possible with NTLMSSP authentication. E.g. NTLMSSP_NEGOTIATE_SIGN and NTLMSSP_NEGOTIATE_SEAL can be cleared by a man in the middle. This was by protocol design in earlier Windows versions.

Windows Server 2003 RTM and Vista RTM introduced a way to protect against the trivial downgrade.

See MsvAvFlags and flag 0x00000002 in https://msdn.microsoft.com/en-us/library/cc236646.aspx

This new feature also implies support for a mechlistMIC when used within SPNEGO, which may prevent downgrades from other SPNEGO mechs, e.g. Kerberos, if sign or seal is finally negotiated.

The Samba implementation doesn't enforce the existence of required flags, which were requested by the application layer, e.g. LDAP or SMB1 encryption (via the unix extensions). As a result a man in the middle can take over the connection. It is also possible to misguide client and/or server to send unencrypted traffic even if encryption was explicitly requested.

LDAP (with NTLMSSP authentication) is used as a client by various admin tools of the Samba project, e.g. "net", "samba-tool", "ldbsearch", "ldbedit", ...

As an active directory member server LDAP is also used by the winbindd service when connecting to domain controllers.

Samba also offers an LDAP server when running as active directory domain controller.

The NTLMSSP authentication used by the SMB1 encryption is protected by smb signing, see CVE-2015-5296.

The following vulnerabilities are related: CVE-2016-2112 and CVE-2016-2113