Category: Security

Monica Rathbun finds trouble with Always Encrypted:

The real challenges started when the client began to test their application code. The first thing we hit was triggers.

The table had several insert triggers associated with the columns that were now encrypted. Since the data was now encrypted the insert triggers would fail. Again, we lucked out and they were able to recode somethings in order to remove the triggers. Of course, since troubles always come in threes, this was no different. First the constraint problem, then the triggers, then we hit the biggest road block that halted our Always Encrypted implementation.

Read on for more information about the things you cannot do with Always Encrypted, including some limitations which will eventually go away.

Bert Wagner hits on the most common reason why you might fail to connect with a SQL authentication login:

I thought it would be best to start with a clean slate so I created a new SQL login and database user so that I could definitively figure out which permissions are needed.

Normally I use Windows Authentication for my logins, but this time I thought “since I’m getting crazy learning new things, let me try creating a SQL Login instead.”

After I created my login, I decided to test connecting to my server before digging into the permissions. Result?

After the fifth or sixth time it happens to you, you start making that the first thing you check.

Eric Blinn shows that dynamic SQL in stored procedures changes the security paradigm a bit:

Security was controlled by granting EXECUTE permissions only to appropriate stored procedures and by explicitly not granting permission to any tables or views within the database.

One of the procedures was getting a bad query plan and timing out. This is when I was called in. The procedure was performing a search based on an unknown number of up to 10 search parameters. The code was filled with many AND/OR combinations to account for the users’ ability to include any combination of search parameters. I found this procedure to be a prime candidate for dynamic SQL where I would create the select statement including only the search parameters entered by the user into the WHERE clause.

Immediately upon testing the users started to receive SELECT permission denied errors. It turns out that when you change to dynamic SQL and call your statement through sp_ExecuteSQL that the permissions are lost. Our options were to grant explicit select permission on the objects or to refactor the code such that it does not use dynamic SQL anymore.

The best solution here would probably be to use a certificate to sign the procedure and give that certificate user rights to select from the tables used in dynamic SQL.

Solomon Rutzky explains how you can use module signing to avoid the security risks which come with impersonation and setting Trustworthy on:

Admittedly, using Cross-Database Ownership Chaining and/or Impersonation and/or TRUSTWORTHY are quicker and easier to implement than Module Signing. However, the relative simplicity in understanding and implementing these options comes at a cost: the security of your system.

• Cross-DB Ownership Chaining:
  • security risk (can spoof User / DB-level)
  • db_ddladmin & db_owner users can create objects for other owners
  • Users with CREATE DATABASE permission can create new databases and attach existing databases
• Impersonation:
  • If IMPERSONATE permission is required:
    • can be used any time
    • No granular control over permissions
  • Cross-DB operations need TRUSTWORTHY ON
  • Need to use ORIGINAL_LOGIN() for Auditing
  • Elevated permissions last until process / sub-process ends or REVERT
• TRUSTWORTHY:
  • Bigger security risk
    • can also spoof Logins, such as “sa” !
    • If using SQLCLR Assemblies, no per-Assembly control of ability to be marked as either EXTERNAL_ACCESS or UNSAFE; all Assemblies are eligible to be marked as either of those elevated permission sets.

The common theme across all three areas is no control, within a Database, over who or what can make use of the feature / option, or when it can be used.

Read the whole thing.