SQL Server must limit the number of concurrent sessions to an organization-defined number per user for all accounts and/or account types.

An XCCDF Rule

Description

Database management includes the ability to control the number of users and user sessions utilizing SQL Server. Unlimited concurrent connections to SQL Server could allow a successful denial-of-service (DoS) attack by exhausting connection resources; and a system can also fail or be degraded by an overload of legitimate users. Limiting the number of concurrent sessions is helpful in reducing these risks. This requirement addresses concurrent session control for a single account. It does not address concurrent sessions by a single user via multiple system accounts. The capability to limit the number of concurrent sessions per user must be configured in or added to SQL Server (for example, by use of a logon trigger), when this is technically feasible. Note that it is not sufficient to limit sessions via a web server or application server alone, because legitimate users and adversaries can potentially connect to SQL Server by other means. The organization will need to define the maximum number of concurrent sessions by account type, by account, or a combination thereof. In deciding on the appropriate number, it is important to consider the work requirements of the various types of users. For example, 2 might be an acceptable limit for general users accessing the database via an application; but 10 might be too few for a database administrator using a database management GUI tool, where each query tab and navigation pane may count as a separate session. (Sessions may also be referred to as connections or logons, which for the purposes of this requirement are synonyms.)

ID: SV-213929r1018580_rule
Version: SQL6-D0-003600
Severity: Medium
References: CCI-000054
Updated: about 2 months ago

Remediation Templates

If a trigger consumes too much CPU, an example alternative method for limiting the concurrent users is setting the max connection limit on SQL Server.

In SQL Server Management Studio's Object Explorer tree, right-click on the Server Name >> Select Properties >> Select Connections Tab >> Set the Maximum Number of Concurrent Connections to a value other than 0 (0 = unlimited), and document it.

OR
Run the query:

EXEC sys.sp_configure N'user connections','5000' /* this is an example max limit */
GO
RECONFIGURE WITH OVERRIDE
GO

Restart SQL Server for the setting to take effect.

Reference: https://learn.microsoft.com/en-us/sql/database-engine/configure-windows/configure-the-user-connections-server-configuration-option?

Otherwise, establish the limit(s) appropriate to the type(s) of user account accessing the SQL Server instance, and record them in the system documentation. Implement one or more logon triggers to enforce the limit(s), without exposing the dynamic management views to general users.  

Example script below:
 
CREATE TRIGGER SQL_STIG_Connection_Limit 
ON ALL SERVER WITH EXECUTE AS 'renamed_sa' /*Make sure to use the renamed SA account here*/ 
FOR LOGON 
AS 
BEGIN 
If (Select COUNT(1) from sys.dm_exec_sessions WHERE is_user_process = 1 AND original_login_name = ORIGINAL_LOGIN() ) > 
  (CASE ORIGINAL_LOGIN()
              WHEN 'domain/ima.dba' THEN 150    /*this is a busy DBA’s domain account */
              WHEN 'application1_login' THEN 6  /* this is a SQL login for an application */
              WHEN 'application2_login' THEN 20 /* this is a SQL login for another application */
              …
              ELSE 1 /* All unspecified users are restricted to a single login */
  END)
              BEGIN 
                             PRINT 'The login [' + ORIGINAL_LOGIN() + '] has exceeded its concurrent session limit.' 
                             ROLLBACK; 
              END
END; 
  
Reference:  https://msdn.microsoft.com/en-us/library/ms189799.aspx

SQL Server must limit the number of concurrent sessions to an organization-defined number per user for all accounts and/or account types.

Description

Remediation Templates

A Manual Procedure