The Windows SMB authentication protocol supports mutual authentication. Mutual authentication closes a "man-in-the-middle" attack. The Windows SMB authentication protocol also supports message authentication. Message authentication helps prevent active message attacks. The client and the server each verify the digital signature. If SMB signing is enabled on a server, clients that are also enabled for SMB signing use the packet signing protocol during all subsequent sessions.
If SMB signing is required on a server, a client cannot establish a session unless the client is enabled or required for SMB signing. Enabling digital signing in high-security networks helps prevent the impersonation of clients and of servers. This kind of impersonation is known as session hijacking. An attacker who has access to the same network as the client or the server uses session hijacking tools to interrupt, end, or steal a session in progress.
An attacker could intercept and modify unsigned SMB packets, modify the traffic, and then forward it so that the server might perform unwanted actions. Or, the attacker could pose as the server or as the client after a legitimate authentication and then gain unauthorized access to data.
Mutual authentication closes session hijacking attacks and supports message authentication. Therefore, it prevents man-in-the-middle attacks. The client and the server then verify the signature. As an alternative countermeasure, you can enable digital signatures with IPSec to help protect all network traffic.
There are hardware-based accelerators for IPSec encryption and signing that you can use to minimize the performance impact from the server's CPU. There are no such accelerators that are available for SMB signing. Configure SMB signing through Group Policy Object Editor because a change to a local registry value has no effect if there is an overriding domain policy.
Additionally, Windows servers do not respond to SMB signing requests from these clients. For more information, see item "Network security: Lan Manager authentication level. Risky configuration The following is a harmful configuration setting: Leaving both the Microsoft network client: Digitally sign communications always setting and the Microsoft network client: Digitally sign communications if server agrees setting set to "Not Defined" or disabled.
These settings allow the redirector to send plain text passwords to non-Microsoft SMB servers that do not support password encryption during authentication. Reasons to enable this setting Enabling Microsoft network client: Digitally sign communications always requires clients to sign SMB traffic when contacting servers that do not require SMB signing. This makes clients less vulnerable to session hijacking attacks. Enabling Microsoft network client: Digitally sign communications always prevents clients from communicating with target servers that do not support SMB signing.
Configuring computers to ignore all unsigned SMB communications prevents earlier programs and operating systems from connecting. You will not be able to map a network drive from a client with this setting enabled, and you will receive the following error message:.
Restart requirements Restart the computer, or restart the Workstation service. To do this, type the following commands at a command prompt. Press Enter after you type each command. An attacker could intercept and modify unsigned Subnet Bandwidth Manager SBM packets, modify the traffic, and then forward it so that the server might perform unwanted actions. Risky configuration The following is a harmful configuration setting: Enabling the Microsoft network server: Digitally sign communications always setting on servers and on domain controllers that are accessed by incompatible Windows-based computers and third-party operating system-based client computers in local or external domains.
All client computers that enable this setting directly through the registry or through the Group Policy setting support SMB signing. In other words, all client computers that have this setting enabled run either Windows 95 with the DS client installed, Windows 98, Windows NT 4. If Microsoft network server: Digitally sign communications always is disabled, SMB signing is completely disabled.
Completely disabling all SMB signing leaves computers more vulnerable to session hijacking attacks. Enabling this setting will prevent clients that cannot negotiate SMB signing from communicating with servers and with domain controllers. This causes operations such as domain joins, user and computer authentication, or network access by programs to fail.
Windows Windows 95 clients that do not have the Directory Services DS Client installed will fail logon authentication and will receive the following error message:. The system could not log you on.
Make sure your username and your domain are correct, then type your password again. Some non-Microsoft SMB servers support only unencrypted password exchanges during authentication. These exchanges also known as "plain text" exchanges. For Windows NT 4. The account is not authorized to login from this station. Windows Server By default, security settings on domain controllers that run Windows Server are configured to help prevent domain controller communications from being intercepted or tampered with by malicious users.
For users to successfully communicate with a domain controller that runs Windows Server , client computers must use both SMB signing and encryption or secure channel traffic signing. By default, clients that run Windows NT 4. Therefore, these clients may not be able to authenticate to a Windows Server based domain controller.
Windows and Windows Server policy settings: Depending on your specific installation needs and configuration, we recommend that you set the following policy settings at the lowest entity of necessary scope in the Microsoft Management Console Group Policy Editor snap-in hierarchy:.
Send unencrypted password to connect to third-party SMB servers this setting is for Windows Microsoft network client: Send unencrypted password to third-party SMB servers this setting is for Windows Server The following clients are incompatible with the Microsoft network server: Digitally sign communications always setting:.
Restart requirements Restart the computer, or restart the Server service. For example, the following operating systems, services, or applications may not work:.
Users in Windows NT 4. Reasons to disable this setting If this setting is enabled, a malicious user could use the well-known Administrators SID to obtain the real name of the built-in Administrator account, even if the account has been renamed.
That person could then use the account name to initiate a password-guessing attack. The Network access: Do not allow anonymous enumeration of SAM accounts setting determines which additional permissions will be granted for anonymous connections to the computer.
Windows allows anonymous users to perform certain activities, such as enumerating the names of workstation and server Security Accounts Manager SAM accounts and of network shares. For example, an administrator can use this to grant access to users in a trusted domain that does not maintain a reciprocal trust.
Once a session is made, an anonymous user may have the same access that is granted to the Everyone group based on the setting in the Network access: Let Everyone permissions apply to anonymous users setting or the discretionary access control list DACL of the object. Typically, anonymous connections are requested by earlier versions of clients down-level clients during SMB session setup.
RPC may also try to make anonymous connections. Important This setting has no impact on domain controllers. In Windows , a similar setting called Additional Restrictions for Anonymous Connections manages the RestrictAnonymous registry value.
The location of this value is as follows. Risky configurations Enabling the Network access: Do not allow anonymous enumeration of SAM accounts setting is a harmful configuration setting from a compatibility perspective. Disabling it is a harmful configuration setting from a security perspective. Reasons to enable this setting An unauthorized user could anonymously list account names and then use the information to try to guess passwords or to perform social engineering attacks.
Social engineering is jargon that means tricking people into revealing their passwords or some form of security information. Reasons to disable this setting If this setting is enabled, it is impossible to establish trusts with Windows NT 4. This setting also causes problems with down-level clients such as Windows NT 3.
Windows 95, Windows Windows 95 clients and Windows 98 clients will not be able to change their passwords. Windows 95, Windows Windows based and Windows based computers will not be able to be authenticated by Microsoft domain controllers. Windows 95, Windows Users on Windows based and Windows based computers will not be able to change the passwords for their user accounts. Windows allows anonymous users to perform certain activities, such as enumerating the names of domain accounts users, computers, and groups and of network shares.
This is convenient, for example, when an administrator wants to grant access to users in a trusted domain that does not maintain a reciprocal trust. If you do not want to allow anonymous enumeration of SAM accounts and of shares, enable this setting.
The location of this value is as follows:. Risky configuration Enabling the Network access: Do not allow anonymous enumeration of SAM accounts and shares setting is a harmful configuration setting.
Enabling the Network access: Do not allow anonymous enumeration of SAM accounts and shares setting prevents enumeration of SAM accounts and shares by users and computers that are using anonymous accounts.
If this setting is enabled, an unauthorized user could anonymously list account names and then use the information to try to guess passwords or to perform social engineering attacks. Social engineering is jargon that means tricking people into revealing their password or some form of security information.
If this setting is enabled, it will be impossible to establish trusts with Windows NT 4. This setting will also cause problems with down-level clients such as Windows NT 3. It will be impossible to grant access to users of resource domains because administrators in the trusting domain will not be able to enumerate lists of accounts in the other domain. Users who access file and print servers anonymously will not be able to list the shared network resources on those servers.
The users must authenticate before they can view the lists of shared folders and printers. The following error message will appear when RestrictAnonymous is enabled on the trusted domain:. Windows Windows based member computers in Windows NT 4. Windows Windows domain users will not be able to add network printers from Active Directory; however, they will be able to add printers after they select them from the tree view. Outlook clients: The global address list will appear empty to Microsoft Exchange Outlook clients.
Additionally, Advanced clients cannot communicate with the Management Point. Anonymous access is required on the Management Point. Background LAN Manager LM authentication is the protocol that is used to authenticate Windows clients for network operations, including domain joins, accessing network resources, and user or computer authentication.
Specifically, the LM authentication level determines which authentication protocols that the client will try to negotiate or that the server will accept.
This value affects the level of authentication protocol that clients use, the level of session security negotiated, and the level of authentication accepted by servers. I have recently inherited a SQL Instance containing a number of databases.
But I don't understand what this user account is Who uses it? Who is able to connect to the database with this user account? Any thoughts? Services that run as the Network Service account access network resources by using the credentials of the computer account. This group implicitly includes all users who are logged on to the system through a dial-up connection.
A group that represents the current owner of the object. When you grant permissions to Principal Self, you grant them to the security principal that is represented by the object. During an access check, the operating system replaces the SID for Principal Self with the SID for the security principal that is represented by the object. This identity represents all users who are currently logged on to a computer by using a Remote Desktop connection.
This group is a subset of the Interactive group. Users and computers with restricted capabilities have the Restricted identity. This identity group is used by a process that is running in a restricted security context, such as running an application with the RunAs service. Any service that accesses the system has the Service identity. This identity group includes all security principals that are signed in as a service.
This identity grants access to processes that are being run by Windows Server services. This identity allows users to access Terminal Server applications and to perform other necessary tasks with Terminal Server services.
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Specifies whether Anonymous authentication is enabled. The default value is true. Optional enum attribute. The logonMethod attribute can be one of the following possible values.
The default is ClearText. Value Description Batch This logon type is intended for batch servers, where processes may be executing on behalf of a user without that user's direct intervention. The numeric value is 1. This logon type preserves the name and password in the authentication package, which allows the server to make connections to other network servers while impersonating the client. The numeric value is 3. This logon type is intended for users who will be using the computer interactively.
The numeric value is 0. This logon type is intended for high performance servers to authenticate plaintext passwords.
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