The SMB1 protocol implementation in Samba 4.x before 4.2.11, 4.3.x before 4.3.8, and 4.4.x before 4.4.2 does not recognize the "server signing = mandatory" setting, which allows man-in-the-middle attackers to spoof SMB servers by modifying the client-server data stream.
http://lists.fedoraproject.org/pipermail/package-announce/2016-April/182185.html
http://lists.fedoraproject.org/pipermail/package-announce/2016-April/182272.html
http://lists.fedoraproject.org/pipermail/package-announce/2016-April/182288.html
http://lists.opensuse.org/opensuse-security-announce/2016-04/msg00047.html
http://lists.opensuse.org/opensuse-security-announce/2016-04/msg00048.html
http://rhn.redhat.com/errata/RHSA-2016-0612.html
http://rhn.redhat.com/errata/RHSA-2016-0614.html
http://rhn.redhat.com/errata/RHSA-2016-0618.html
http://rhn.redhat.com/errata/RHSA-2016-0620.html
http://www.debian.org/security/2016/dsa-3548
http://www.oracle.com/technetwork/topics/security/linuxbulletinapr2016-2952096.html
http://www.securityfocus.com/bid/86011
http://www.securitytracker.com/id/1035533
http://www.slackware.com/security/viewer.php?l=slackware-security&y=2016&m=slackware-security.458012
http://www.ubuntu.com/usn/USN-2950-1
http://www.ubuntu.com/usn/USN-2950-2
http://www.ubuntu.com/usn/USN-2950-3
http://www.ubuntu.com/usn/USN-2950-4
http://www.ubuntu.com/usn/USN-2950-5
https://bto.bluecoat.com/security-advisory/sa122
https://security.gentoo.org/glsa/201612-47
https://www.samba.org/samba/history/samba-4.2.10.html
Source: MITRE
Published: 2016-04-25
Updated: 2016-12-31
Type: CWE-254
Base Score: 4.3
Vector: AV:N/AC:M/Au:N/C:N/I:P/A:N
Impact Score: 2.9
Exploitability Score: 8.6
Severity: MEDIUM
Base Score: 5.9
Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
Impact Score: 3.6
Exploitability Score: 2.2
Severity: MEDIUM