RHSA-2016:0620 - Security Advisory

Topic

An update for samba4 is now available for Red Hat Enterprise Linux 6.2 Advanced
Update Support, Red Hat Enterprise Linux 6.4 Advanced Update Support, Red Hat
Enterprise Linux 6.5 Advanced Update Support, and Red Hat Enterprise Linux 6.6
Extended Update Support.

Red Hat Product Security has rated this update as having a security impact of
Critical. A Common Vulnerability Scoring System (CVSS) base score, which gives a
detailed severity rating, is available for each vulnerability from the CVE
link(s) in the References section.

Description

Samba is an open-source implementation of the Server Message Block (SMB) or
Common Internet File System (CIFS) protocol, which allows PC-compatible machines
to share files, printers, and other information.

The following packages have been upgraded to a newer upstream version: Samba
(4.2.10). Refer to the Release Notes listed in the References section for a
complete list of changes.

Security Fix(es):

• Multiple flaws were found in Samba's DCE/RPC protocol implementation. A

remote, authenticated attacker could use these flaws to cause a denial of
service against the Samba server (high CPU load or a crash) or, possibly,
execute arbitrary code with the permissions of the user running Samba (root).
This flaw could also be used to downgrade a secure DCE/RPC connection by a
man-in-the-middle attacker taking control of an Active Directory (AD) object and
compromising the security of a Samba Active Directory Domain Controller (DC).
(CVE-2015-5370)

Note: While Samba packages as shipped in Red Hat Enterprise Linux do not support
running Samba as an AD DC, this flaw applies to all roles Samba implements.

• A protocol flaw, publicly referred to as Badlock, was found in the Security

Account Manager Remote Protocol (MS-SAMR) and the Local Security Authority
(Domain Policy) Remote Protocol (MS-LSAD). Any authenticated DCE/RPC connection
that a client initiates against a server could be used by a man-in-the-middle
attacker to impersonate the authenticated user against the SAMR or LSA service
on the server. As a result, the attacker would be able to get read/write access
to the Security Account Manager database, and use this to reveal all passwords
or any other potentially sensitive information in that database. (CVE-2016-2118)

• Several flaws were found in Samba's implementation of NTLMSSP authentication.

An unauthenticated, man-in-the-middle attacker could use this flaw to clear the
encryption and integrity flags of a connection, causing data to be transmitted
in plain text. The attacker could also force the client or server into sending
data in plain text even if encryption was explicitly requested for that
connection. (CVE-2016-2110)

• It was discovered that Samba configured as a Domain Controller would establish

a secure communication channel with a machine using a spoofed computer name. A
remote attacker able to observe network traffic could use this flaw to obtain
session-related information about the spoofed machine. (CVE-2016-2111)

• It was found that Samba's LDAP implementation did not enforce integrity

protection for LDAP connections. A man-in-the-middle attacker could use this
flaw to downgrade LDAP connections to use no integrity protection, allowing them
to hijack such connections. (CVE-2016-2112)

• It was found that Samba did not validate SSL/TLS certificates in certain

connections. A man-in-the-middle attacker could use this flaw to spoof a Samba
server using a specially crafted SSL/TLS certificate. (CVE-2016-2113)

• It was discovered that Samba did not enforce Server Message Block (SMB)

signing for clients using the SMB1 protocol. A man-in-the-middle attacker could
use this flaw to modify traffic between a client and a server. (CVE-2016-2114)

• It was found that Samba did not enable integrity protection for IPC traffic by

default. A man-in-the-middle attacker could use this flaw to view and modify the
data sent between a Samba server and a client. (CVE-2016-2115)

Red Hat would like to thank the Samba project for reporting these issues.
Upstream acknowledges Jouni Knuutinen (Synopsis) as the original reporter of
CVE-2015-5370; and Stefan Metzmacher (SerNet) as the original reporter of
CVE-2016-2118, CVE-2016-2110, CVE-2016-2112, CVE-2016-2113, CVE-2016-2114, and
CVE-2016-2115.

Solution

For details on how to apply this update, which includes the changes described in
this advisory, refer to:

https://access.redhat.com/articles/11258

After installing this update, the smb service will be restarted automatically.

Affected Products

• Red Hat Enterprise Linux for x86_64 - Extended Update Support 6.6 x86_64
• Red Hat Enterprise Linux for x86_64 - Extended Update Support 6.6 i386
• Red Hat Enterprise Linux Server - AUS 6.6 x86_64
• Red Hat Enterprise Linux Server - AUS 6.5 x86_64
• Red Hat Enterprise Linux Server - AUS 6.4 x86_64
• Red Hat Enterprise Linux Server - AUS 6.2 x86_64
• Red Hat Enterprise Linux for IBM z Systems - Extended Update Support 6.6 s390x
• Red Hat Enterprise Linux for Power, big endian - Extended Update Support 6.6 ppc64
• Red Hat Enterprise Linux Server - TUS 6.6 x86_64
• Red Hat Enterprise Linux Server - TUS 6.5 x86_64
• Red Hat Enterprise Linux Server - Extended Update Support from RHUI 6.6 x86_64
• Red Hat Enterprise Linux Server - Extended Update Support from RHUI 6.6 i386
• Red Hat Enterprise Linux EUS Compute Node 6.6 x86_64

Fixes

• BZ - 1309987 - CVE-2015-5370 samba: crash in dcesrv_auth_bind_ack due to missing error check
• BZ - 1311893 - CVE-2016-2110 samba: Man-in-the-middle attacks possible with NTLMSSP authentication
• BZ - 1311902 - CVE-2016-2111 samba: Spoofing vulnerability when domain controller is configured
• BZ - 1311903 - CVE-2016-2112 samba: Missing downgrade detection
• BZ - 1311910 - CVE-2016-2113 samba: Server certificates not validated at client side
• BZ - 1312082 - CVE-2016-2114 samba: Samba based active directory domain controller does not enforce smb signing
• BZ - 1312084 - CVE-2016-2115 samba: Smb signing not required by default when smb client connection is used for ipc usage
• BZ - 1317990 - CVE-2016-2118 samba: SAMR and LSA man in the middle attacks

CVEs

• CVE-2015-5370
• CVE-2016-2115
• CVE-2016-2112
• CVE-2016-2118
• CVE-2016-2111
• CVE-2016-2110
• CVE-2016-2114
• CVE-2016-2113

References

• https://access.redhat.com/security/updates/classification/#critical
• https://www.samba.org/samba/history/samba-4.2.10.html
• https://access.redhat.com/security/vulnerabilities/badlock
• https://access.redhat.com/articles/2253041
• http://badlock.org/
• https://access.redhat.com/articles/2243351