DSA-3740-1

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.

A flaw was found in samba versions 4.0.0 to 4.5.2. The Samba routine ndr_pull_dnsp_name contains an integer wrap problem, leading to an attacker-controlled memory overwrite. ndr_pull_dnsp_name parses data from the Samba Active Directory ldb database. Any user who can write to the dnsRecord attribute over LDAP can trigger this memory corruption. By default, all authenticated LDAP users can write to the dnsRecord attribute on new DNS objects. This makes the defect a remote privilege escalation.

It was found that Samba before versions 4.5.3, 4.4.8, 4.3.13 always requested forwardable tickets when using Kerberos authentication. A service to which Samba authenticated using Kerberos could subsequently use the ticket to impersonate Samba to other services or domain users.

Samba version 4.0.0 up to 4.5.2 is vulnerable to privilege elevation due to incorrect handling of the PAC (Privilege Attribute Certificate) checksum. A remote, authenticated, attacker can cause the winbindd process to crash using a legitimate Kerberos ticket. A local service with access to the winbindd privileged pipe can cause winbindd to cache elevated access permissions.