Karolin Seeger
2016-Apr-12 17:12 UTC
[Announce] Samba 4.4.2, 4.3.8 and 4.2.11 Available for Download
Release Announcements --------------------- This is a security release in order to address the following CVEs: o CVE-2015-5370 (Multiple errors in DCE-RPC code) o CVE-2016-2110 (Man in the middle attacks possible with NTLMSSP) o CVE-2016-2111 (NETLOGON Spoofing Vulnerability) o CVE-2016-2112 (LDAP client and server don't enforce integrity) o CVE-2016-2113 (Missing TLS certificate validation) o CVE-2016-2114 ("server signing = mandatory" not enforced) o CVE-2016-2115 (SMB IPC traffic is not integrity protected) o CVE-2016-2118 (SAMR and LSA man in the middle attacks possible) The number of changes are rather huge for a security release, compared to typical security releases. Given the number of problems and the fact that they are all related to man in the middle attacks we decided to fix them all at once instead of splitting them. In order to prevent the man in the middle attacks it was required to change the (default) behavior for some protocols. Please see the "New smb.conf options" and "Behavior changes" sections below. Affected Versions: 3.6.x, 4.0.x, 4.1.x, 4.2.0-4.2.9, 4.3.0-4.3.6, 4.4.0 (earlier versions have not been assessed) Patched Versions: 4.2.10 / 4.2.11, 4.3.7 / 4.3.8 and 4.4.1 / 4.4.2 (both the interim and final security release have the patches). Some vendors may choose to ship 4.4.1, 4.3.7, and 4.2.10 versions and add regression patches on top of them, due to wide scale and complexity of this release. Some may also just backport the patches to older releases. Please contact your Samba supplier for details. Pre 4.2 versions have been discontinued (see https://wiki.samba.org/index.php/Samba_Release_Planning). Upgrading to a supported version is recommended. Some vendors have backported the patches to earlier versions. =======Summary: ======= These releases fix multiple security vulnerabilities in the software and change the default behavior for some protocols. The security vulnerabilities can be mostly categorised as man in the middle or denial of service attacks. 1. Man in the middle (MITM) attacks There are several MITM attacks that can be performed against a variety of protocols used by Samba. These would permit execution of arbitrary Samba network calls using the context of the intercepted user. Impact examples of intercepting administrator network traffic: * Samba AD server - view or modify secrets within an AD database, including user password hashes, or shutdown critical services. * standard Samba server - modify user permissions on files or directories. To execute a man in the middle attack requires an attacker to manipulate network traffic in the local network segment of the client or server. Mitigations: Network protections that could be used MITM attacks include DHCP snooping, ARP Inspection and 802.1x. Suggested further improvements after patching: It is recommended that administrators set these additional options, if compatible with their network environment: server signing = mandatory ntlm auth = no Without "server signing = mandatory", man in the middle attacks are still possible against our file server and classic/NT4-like/Samba3 Domain controller. (It is now enforced on Samba's AD DC.) Note that this has heavy impact on the file server performance, so you need to decide between performance and security. These man in the middle attacks for smb file servers are well known for decades. Without "ntlm auth = no", there may still be clients not using NTLMv2, and these observed passwords may be brute-forced easily using cloud-computing resources or rainbow tables. 2. Denial of Service (DoS) Samba services are vulnerable to a denial of service from an attacker with remote network connectivity to the Samba service. Mitigation: Apply firewall rules on the server to permit connectivity only from trusted addresses. Will encryption protect against these attacks? The SMB protocol, by default, only encrypts credentials and commands while files are transferred in plaintext. It is recommended that in security / privacy sensitive scenarios encryption is used to protect all communications. Samba added encryption in version 3.2 in 2008, but only for Samba clients. Microsoft added SMB encryption support to SMB 3.0 in Windows 8 and Windows Server 2012. However, both of these types of encryption only protect communications, such a file transfers, after SMB negotiation and commands have been completed. It is this phase that contains the fixed vulnerabilities. Samba/SMB encryption is good practice but is not sufficient for protection against these vulnerabilities. Network-level encryption, such as IPSec, is required for full protection as a workaround. ===================================New Options and Defaults (highlevel) =================================== The security updates include new smb.conf options and a number of stricter behaviors to prevent Man in the Middle attacks on our network services, as a client and as a server. Between these changes, compatibility with a large number of older software versions has been lost in the default configuration. See https://www.samba.org/samba/history/samba-4.4.2.html for more information. Here are some additional hints how to work around the new stricter default behaviors: * As an AD DC server, only Windows 2000 and Samba 3.6 and above as a domain member are supported out of the box. Other smb file servers as domain members are also fine out of the box. * As an AD DC server, with default setting of "ldap server require strong auth", LDAP clients connecting over ldaps:// or START_TLS will be allowed to perform simple LDAP bind only. The preferred configuration for LDAP clients is to use SASL GSSAPI directly over ldap:// without using ldaps:// or START_TLS. To use LDAP with START_TLS and SASL GSSAPI (either Kerberos or NTLMSSP) sign/seal protection must be used by the client and server should be configured with "ldap server require strong auth = allow_sasl_over_tls". Consult OpenLDAP documentation how to set sign/seal protection in ldap.conf. For SSSD client configured with "id_provider = ad" or "id_provider = ldap" with "auth_provider = krb5", see sssd-ldap(5) manual for details on TLS session handling. * As a File Server, compatibility with the Linux Kernel cifs client depends on which configuration options are selected, please use "sec=krb5(i)" or "sec=ntlmssp(i)", not "sec=ntlmv2". * As a file or printer client and as a domain member, out of the box compatibility with Samba less than 4.0 and other SMB/CIFS servers, depends on support for SMB signing or SMB2 on the server, which is often disabled or absent. You may need to adjust the "client ipc signing" to "no" in these cases. * In case of an upgrade from versions before 4.2.0, you might run into problems as a domain member. The out of the box compatibility with Samba 3.x domain controllers requires NETLOGON features only available in Samba 3.2 and above. However, all of these can be worked around by setting smb.conf options in Samba, see https://www.samba.org/samba/history/samba-4.2.0.html and the Samba wiki for details, workarounds and suggested security-improving changes to these and other software packages. You might run into a regression that will prevent users from trusted domains to be authenticated on a domain member server and related problems. You can indentify the bug by debug messages at log level 1 in log.wb-* similar to: Unwilling to make connection to domain OTHERDOMAIN without connection level security, must set "winbind sealed pipes = false" and "require strong key = false" to proceed: NT_STATUS_DOWNGRADE_DETECTED Note that there is a workaround by changing the configuration: The workaround consists in adding the following to the [global] section of the smb.conf on the domain member server. In the example you would have "workgroup = PRIMARYDOMAIN". winbind sealed pipes = false require strong key = false winbind sealed pipes:PRIMARYDOMAIN = true require strong key:PRIMARYDOMAIN = true For further information see https://bugzilla.samba.org/show_bug.cgi?id=11830 Some vendors may already include a patch that changes the default values for these options. Typically if they upgraded from versions before 4.2.0. ======Details ====== o CVE-2015-5370 Versions of Samba from 3.6.0 to 4.4.0 inclusive are vulnerable to denial of service attacks (crashes and high cpu consumption) in the DCE-RPC client and server implementations. In addition, errors in validation of the DCE-RPC packets can lead to a downgrade of a secure connection to an insecure one. While we think it is unlikely, there's a nonzero chance for a remote code execution attack against the client components, which are used by smbd, winbindd and tools like net, rpcclient and others. This may gain root access to the attacker. The above applies all possible server roles Samba can operate in. Note that versions before 3.6.0 had completely different marshalling functions for the generic DCE-RPC layer. It's quite possible that that code has similar problems! The downgrade of a secure connection to an insecure one may allow an attacker to take control of Active Directory object handles created on a connection created from an Administrator account and re-use them on the now non-privileged connection, compromising the security of the Samba AD-DC. o CVE-2016-2110: 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. o CVE-2016-2111: It's basically the same as CVE-2015-0005 for Windows: The NETLOGON service in Microsoft Windows Server 2003 SP2, Windows Server 2008 SP2 and R2 SP1, and Windows Server 2012 Gold and R2, when a Domain Controller is configured, allows remote attackers to spoof the computer name of a secure channel's endpoint, and obtain sensitive session information, by running a crafted application and leveraging the ability to sniff network traffic, aka "NETLOGON Spoofing Vulnerability". The vulnerability in Samba is worse as it doesn't require credentials of a computer account in the domain. This only applies to Samba running as classic primary domain controller, classic backup domain controller or active directory domain controller. The security patches introduce a new option called "raw NTLMv2 auth" ("yes" or "no") for the [global] section in smb.conf. Samba (the smbd process) will reject client using raw NTLMv2 without using NTLMSSP. Note that this option also applies to Samba running as standalone server and member server. You should also consider using "lanman auth = no" (which is already the default) and "ntlm auth = no". Have a look at the smb.conf manpage for further details, as they might impact compatibility with older clients. These also apply for all server roles. o CVE-2016-2112: Samba uses various LDAP client libraries, a builtin one and/or the system ldap libraries (typically openldap). As active directory domain controller Samba also provides an LDAP server. Samba takes care of doing SASL (GSS-SPNEGO) authentication with Kerberos or NTLMSSP for LDAP connections, including possible integrity (sign) and privacy (seal) protection. Samba has support for an option called "client ldap sasl wrapping" since version 3.2.0. Its default value has changed from "plain" to "sign" with version 4.2.0. Tools using the builtin LDAP client library do not obey the "client ldap sasl wrapping" option. This applies to tools like: "samba-tool", "ldbsearch", "ldbedit" and more. Some of them have command line options like "--sign" and "--encrypt". With the security update they will also obey the "client ldap sasl wrapping" option as default. In all cases, even if explicitly request via "client ldap sasl wrapping", "--sign" or "--encrypt", the protection can be downgraded by a man in the middle. The LDAP server doesn't have an option to enforce strong authentication yet. The security patches will introduce a new option called "ldap server require strong auth", possible values are "no", "allow_sasl_over_tls" and "yes". As the default behavior was as "no" before, you may have to explicitly change this option until all clients have been adjusted to handle LDAP_STRONG_AUTH_REQUIRED errors. Windows clients and Samba member servers already use integrity protection. o CVE-2016-2113: Samba has support for TLS/SSL for some protocols: ldap and http, but currently certificates are not validated at all. While we have a "tls cafile" option, the configured certificate is not used to validate the server certificate. This applies to ldaps:// connections triggered by tools like: "ldbsearch", "ldbedit" and more. Note that it only applies to the ldb tools when they are built as part of Samba or with Samba extensions installed, which means the Samba builtin LDAP client library is used. It also applies to dcerpc client connections using ncacn_http (with https://), which are only used by the openchange project. Support for ncacn_http was introduced in version 4.2.0. The security patches will introduce a new option called "tls verify peer". Possible values are "no_check", "ca_only", "ca_and_name_if_available", "ca_and_name" and "as_strict_as_possible". If you use the self-signed certificates which are auto-generated by Samba, you won't have a crl file and need to explicitly set "tls verify peer = ca_and_name". o CVE-2016-2114 Due to a regression introduced in Samba 4.0.0, an explicit "server signing = mandatory" in the [global] section of the smb.conf was not enforced for clients using the SMB1 protocol. As a result it does not enforce smb signing and allows man in the middle attacks. This problem applies to all possible server roles: standalone server, member server, classic primary domain controller, classic backup domain controller and active directory domain controller. In addition, when Samba is configured with "server role = active directory domain controller" the effective default for the "server signing" option should be "mandatory". During the early development of Samba 4 we had a new experimental file server located under source4/smb_server. But before the final 4.0.0 release we switched back to the file server under source3/smbd. But the logic for the correct default of "server signing" was not ported correctly ported. Note that the default for server roles other than active directory domain controller, is "off" because of performance reasons. o CVE-2016-2115: Samba has an option called "client signing", this is turned off by default for performance reasons on file transfers. This option is also used when using DCERPC with ncacn_np. In order to get integrity protection for ipc related communication by default the "client ipc signing" option is introduced. The effective default for this new option is "mandatory". In order to be compatible with more SMB server implementations, the following additional options are introduced: "client ipc min protocol" ("NT1" by default) and "client ipc max protocol" (the highest support SMB2/3 dialect by default). These options overwrite the "client min protocol" and "client max protocol" options, because the default for "client max protocol" is still "NT1". The reason for this is the fact that all SMB2/3 support SMB signing, while there are still SMB1 implementations which don't offer SMB signing by default (this includes Samba versions before 4.0.0). Note that winbindd (in versions 4.2.0 and higher) enforces SMB signing against active directory domain controllers despite of the "client signing" and "client ipc signing" options. o CVE-2016-2118 (a.k.a. BADLOCK): The Security Account Manager Remote Protocol [MS-SAMR] and the Local Security Authority (Domain Policy) Remote Protocol [MS-LSAD] are both vulnerable to man in the middle attacks. Both are application level protocols based on the generic DCE 1.1 Remote Procedure Call (DCERPC) protocol. These protocols are typically available on all Windows installations as well as every Samba server. They are used to maintain the Security Account Manager Database. This applies to all roles, e.g. standalone, domain member, domain controller. Any authenticated DCERPC connection a client initiates against a server can be used by a man in the middle to impersonate the authenticated user against the SAMR or LSAD service on the server. The client chosen application protocol, auth type (e.g. Kerberos or NTLMSSP) and auth level (NONE, CONNECT, PKT_INTEGRITY, PKT_PRIVACY) do not matter in this case. A man in the middle can change auth level to CONNECT (which means authentication without message protection) and take over the connection. As a result, a man in the middle is able to get read/write access to the Security Account Manager Database, which reveals all passwords and any other potential sensitive information. Samba running as an active directory domain controller is additionally missing checks to enforce PKT_PRIVACY for the Directory Replication Service Remote Protocol [MS-DRSR] (drsuapi) and the BackupKey Remote Protocol [MS-BKRP] (backupkey). The Domain Name Service Server Management Protocol [MS-DNSP] (dnsserver) is not enforcing at least PKT_INTEGRITY. ===================New smb.conf options =================== allow dcerpc auth level connect (G) This option controls whether DCERPC services are allowed to be used with DCERPC_AUTH_LEVEL_CONNECT, which provides authentication, but no per message integrity nor privacy protection. Some interfaces like samr, lsarpc and netlogon have a hard-coded default of no and epmapper, mgmt and rpcecho have a hard-coded default of yes. The behavior can be overwritten per interface name (e.g. lsarpc, netlogon, samr, srvsvc, winreg, wkssvc ...) by using 'allow dcerpc auth level connect:interface = yes' as option. This option yields precedence to the implementation specific restrictions. E.g. the drsuapi and backupkey protocols require DCERPC_AUTH_LEVEL_PRIVACY. The dnsserver protocol requires DCERPC_AUTH_LEVEL_INTEGRITY. Default: allow dcerpc auth level connect = no Example: allow dcerpc auth level connect = yes client ipc signing (G) This controls whether the client is allowed or required to use SMB signing for IPC$ connections as DCERPC transport. Possible values are auto, mandatory and disabled. When set to mandatory or default, SMB signing is required. When set to auto, SMB signing is offered, but not enforced and if set to disabled, SMB signing is not offered either. Connections from winbindd to Active Directory Domain Controllers always enforce signing. Default: client ipc signing = default client ipc max protocol (G) The value of the parameter (a string) is the highest protocol level that will be supported for IPC$ connections as DCERPC transport. Normally this option should not be set as the automatic negotiation phase in the SMB protocol takes care of choosing the appropriate protocol. The value default refers to the latest supported protocol, currently SMB3_11. See client max protocol for a full list of available protocols. The values CORE, COREPLUS, LANMAN1, LANMAN2 are silently upgraded to NT1. Default: client ipc max protocol = default Example: client ipc max protocol = SMB2_10 client ipc min protocol (G) This setting controls the minimum protocol version that the will be attempted to use for IPC$ connections as DCERPC transport. Normally this option should not be set as the automatic negotiation phase in the SMB protocol takes care of choosing the appropriate protocol. The value default refers to the higher value of NT1 and the effective value of "client min protocol". See client max protocol for a full list of available protocols. The values CORE, COREPLUS, LANMAN1, LANMAN2 are silently upgraded to NT1. Default: client ipc min protocol = default Example: client ipc min protocol = SMB3_11 ldap server require strong auth (G) The ldap server require strong auth defines whether the ldap server requires ldap traffic to be signed or signed and encrypted (sealed). Possible values are no, allow_sasl_over_tls and yes. A value of no allows simple and sasl binds over all transports. A value of allow_sasl_over_tls allows simple and sasl binds (without sign or seal) over TLS encrypted connections. Unencrypted connections only allow sasl binds with sign or seal. A value of yes allows only simple binds over TLS encrypted connections. Unencrypted connections only allow sasl binds with sign or seal. Default: ldap server require strong auth = yes raw NTLMv2 auth (G) This parameter determines whether or not smbd(8) will allow SMB1 clients without extended security (without SPNEGO) to use NTLMv2 authentication. If this option, lanman auth and ntlm auth are all disabled, then only clients with SPNEGO support will be permitted. That means NTLMv2 is only supported within NTLMSSP. Default: raw NTLMv2 auth = no tls verify peer (G) This controls if and how strict the client will verify the peer's certificate and name. Possible values are (in increasing order): no_check, ca_only, ca_and_name_if_available, ca_and_name and as_strict_as_possible. When set to no_check the certificate is not verified at all, which allows trivial man in the middle attacks. When set to ca_only the certificate is verified to be signed from a ca specified in the "tls ca file" option. Setting "tls ca file" to a valid file is required. The certificate lifetime is also verified. If the "tls crl file" option is configured, the certificate is also verified against the ca crl. When set to ca_and_name_if_available all checks from ca_only are performed. In addition, the peer hostname is verified against the certificate's name, if it is provided by the application layer and not given as an ip address string. When set to ca_and_name all checks from ca_and_name_if_available are performed. In addition the peer hostname needs to be provided and even an ip address is checked against the certificate's name. When set to as_strict_as_possible all checks from ca_and_name are performed. In addition the "tls crl file" needs to be configured. Future versions of Samba may implement additional checks. Default: tls verify peer = as_strict_as_possible tls priority (G) (backported from Samba 4.3 to Samba 4.2) This option can be set to a string describing the TLS protocols to be supported in the parts of Samba that use GnuTLS, specifically the AD DC. The default turns off SSLv3, as this protocol is no longer considered secure after CVE-2014-3566 (otherwise known as POODLE) impacted SSLv3 use in HTTPS applications. The valid options are described in the GNUTLS Priority-Strings documentation at http://gnutls.org/manual/html_node/Priority-Strings.html Default: tls priority = NORMAL:-VERS-SSL3.0 ===============Behavior changes =============== o The default auth level for authenticated binds has changed from DCERPC_AUTH_LEVEL_CONNECT to DCERPC_AUTH_LEVEL_INTEGRITY. That means ncacn_ip_tcp:server is now implicitly the same as ncacn_ip_tcp:server[sign] and offers a similar protection as ncacn_np:server, which relies on smb signing. o The following constraints are applied to SMB1 connections: - "client lanman auth = yes" is now consistently required for authenticated connections using the SMB1 LANMAN2 dialect. - "client ntlmv2 auth = yes" and "client use spnego = yes" (both the default values), require extended security (SPNEGO) support from the server. That means NTLMv2 is only used within NTLMSSP. o Tools like "samba-tool", "ldbsearch", "ldbedit" and more obey the default of "client ldap sasl wrapping = sign". Even with "client ldap sasl wrapping = plain" they will automatically upgrade to "sign" when getting LDAP_STRONG_AUTH_REQUIRED from the LDAP server. Changes since 4.4.0: =================== o Jeremy Allison <jra at samba.org> * Bug 11344 - CVE-2015-5370: Multiple errors in DCE-RPC code. o Christian Ambach <ambi at samba.org> * Bug 11804 - prerequisite backports for the security release on April 12th, 2016. o Ralph Boehme <slow at samba.org> * Bug 11644 - CVE-2016-2112: The LDAP client and server don't enforce integrity protection. o Günther Deschner <gd at samba.org> * Bug 11749 - CVE-2016-2111: NETLOGON Spoofing Vulnerability. * Bug 11804 - prerequisite backports for the security release on April 12th, 2016. o Volker Lendecke <vl at samba.org> * Bug 11804 - prerequisite backports for the security release on April 12th, 2016. o Stefan Metzmacher <metze at samba.org> * Bug 11344 - CVE-2015-5370: Multiple errors in DCE-RPC code. * Bug 11616 - CVE-2016-2118: SAMR and LSA man in the middle attacks possible. * Bug 11644 - CVE-2016-2112: The LDAP client and server doesn't enforce integrity protection. * Bug 11687 - CVE-2016-2114: "server signing = mandatory" not enforced. * Bug 11688 - CVE-2016-2110: Man in the middle attacks possible with NTLMSSP. * Bug 11749 - CVE-2016-2111: NETLOGON Spoofing Vulnerability. * Bug 11752 - CVE-2016-2113: Missing TLS certificate validation allows man in the middle attacks. * Bug 11756 - CVE-2016-2115: SMB client connections for IPC traffic are not integrity protected. * Bug 11804 - prerequisite backports for the security release on April 12th, 2016. ####################################### Reporting bugs & Development Discussion ####################################### Please discuss this release on the samba-technical mailing list or by joining the #samba-technical IRC channel on irc.freenode.net. If you do report problems then please try to send high quality feedback. If you don't provide vital information to help us track down the problem then you will probably be ignored. All bug reports should be filed under the "Samba 4.1 and newer" product in the project's Bugzilla database (https://bugzilla.samba.org/). ======================================================================= Our Code, Our Bugs, Our Responsibility. == The Samba Team ===================================================================== ==========================Attention for Samba vendors ========================== If you represent an existing vendor that ships Samba in their products, consider registering with Samba Team. To do so, please send details about your product, security contact person list (with individual email addresses), and GPG key fingerprint to security at samba.org, from your official corporate email address. Please register with the Samba Bugzilla instance using the same email address(es). ===============Download Details =============== The uncompressed tarballs and patch files have been signed using GnuPG (ID 6568B7EA). The source code can be downloaded from: https://download.samba.org/pub/samba/stable/ Patches addressing this defect have been posted to https://www.samba.org/samba/history/security.html The release notes are available online at: https://www.samba.org/samba/history/samba-4.4.2.html https://www.samba.org/samba/history/samba-4.3.8.html https://www.samba.org/samba/history/samba-4.2.11.html Our Code, Our Bugs, Our Responsibility. (https://bugzilla.samba.org/) --Enjoy The Samba Team -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 181 bytes Desc: Digital signature URL: <http://lists.samba.org/pipermail/samba-announce/attachments/20160412/bd162e43/signature-0001.sig>
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