CLR strict security

Applies to: SQL Server

Controls the interpretation of the SAFE, EXTERNAL ACCESS, UNSAFE permission in SQL Server.

Value Description
0 Disabled - Provided for backwards compatibility. Disabled value is not recommended.
1 Enabled - Causes the Database Engine to ignore the PERMISSION_SET information on the assemblies, and always interpret them as UNSAFE. Enabled is the default value, starting with SQL Server 2017 (14.x).


CLR uses Code Access Security (CAS) in the .NET Framework, which is no longer supported as a security boundary. A CLR assembly created with PERMISSION_SET = SAFE may be able to access external system resources, call unmanaged code, and acquire sysadmin privileges. Beginning with SQL Server 2017 (14.x), an sp_configure option called clr strict security is introduced to enhance the security of CLR assemblies. clr strict security is enabled by default, and treats SAFE and EXTERNAL_ACCESS assemblies as if they were marked UNSAFE. The clr strict security option can be disabled for backward compatibility, but this is not recommended. Microsoft recommends that all assemblies be signed by a certificate or asymmetric key with a corresponding login that has been granted UNSAFE ASSEMBLY permission in the master database. SQL Server administrators can also add assemblies to a list of assemblies, which the Database Engine should trust. For more information, see sys.sp_add_trusted_assembly.


When enabled, the PERMISSION_SET option in the CREATE ASSEMBLY and ALTER ASSEMBLY statements is ignored at run-time, but the PERMISSION_SET options are preserved in metadata. Ignoring the option, minimizes breaking existing code statements.

CLR strict security is an advanced option.


After enabling strict security, any assemblies that are not signed will fail to load. You must either alter or drop and recreate each assembly so that it is signed with a certificate or asymmetric key that has a corresponding login with the UNSAFE ASSEMBLY permission on the server.


To change this option

Requires CONTROL SERVER permission, or membership in the sysadmin fixed server role.

To create an CLR assembly

The following permissions required to create a CLR assembly when CLR strict security is enabled:

  • The user must have the CREATE ASSEMBLY permission
  • And one of the following conditions must also be true:
    • The assembly is signed with a certificate or asymmetric key that has a corresponding login with the UNSAFE ASSEMBLY permission on the server. Signing the assembly is recommended.
    • The database has the TRUSTWORTHY property set to ON, and the database is owned by a login that has the UNSAFE ASSEMBLY permission on the server. This option is not recommended.

See Also

Server Configuration Options (SQL Server)
sp_configure (Transact-SQL)
clr enabled Server Configuration Option