libcli/smb/smbXcli_base.c in Samba 4.x before 4.2.14, 4.3.x before 4.3.11, and 4.4.x before 4.4.5 allows man-in-the-middle attackers to bypass a client-signing protection mechanism, and consequently spoof SMB2 and SMB3 servers, via the (1) SMB2_SESSION_FLAG_IS_GUEST or (2) SMB2_SESSION_FLAG_IS_NULL flag.
Exploitability
AV:NAC:HPR:NUI:RScope
S:UImpact
C:HI:HA:H7.5/CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H