Using a Certificate Signed Stored Procedure to Execute sp_send_dbmail

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Using a Certificate Signed Stored Procedure to Execute sp_send_dbmail

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FreeHansje SSChampion Points: 11751 More actions · Answer 1

I thought I had found the solution for my problem, but alas...

I need to call master.sys.dm_exec_sql_text(to find the last used sql-statement) from a trigger, or sp, in another database, by ordinary users without SA-rights; please don't ask why.

I changed reference in your article from msdb into master, used GRANT VIEW SERVER STATE as authorization, but alas, no succes. For days now I am looking for a way to allow non-SA users to view DMV's. Any1 here can help me out?!

Greetz,
Hans Brouwer

Jonathan Kehayias One Orange Chip Points: 26778 More actions · Answer 2

FreeHansje (1/11/2010)
I thought I had found the solution for my problem, but alas...
I need to call master.sys.dm_exec_sql_text(to find the last used sql-statement) from a trigger, or sp, in another database, by ordinary users without SA-rights; please don't ask why.
I changed reference in your article from msdb into master, used GRANT VIEW SERVER STATE as authorization, but alas, no succes. For days now I am looking for a way to allow non-SA users to view DMV's. Any1 here can help me out?!

You actually don't need any kind of special permissions to solve your problem. First sys.dm_exec_sql_text isn't going to give you the information that you probably want. If you run that for a session_id in a trigger, it is going to return the CREATE TRIGGER statement of the trigger firing the request. As long as the need to get the SQL Statement that was executed to cause the trigger to fire is self session scoped, you can get it without added permissions using DBCC INPUTBUFFER() like follows:

CREATE TABLE PermsTest

(RowID int identity primary key)

GO

CREATE TRIGGER Audit_PermsTest

ON PermsTest

WITH EXECUTE AS OWNER

FOR INSERT, UPDATE, DELETE

AS

BEGIN

DECLARE @TEMP TABLE

(EventType nvarchar(30), Parameters int, EventInfo nvarchar(4000))

INSERT INTO @TEMP EXEC('DBCC INPUTBUFFER(@@SPID)')

SELECT EventInfo FROM @TEMP

END

GO

If you want to get information from another session that is executing that would require the additional permissions. As long as it stays self scoped it can be called without GRANT VIEW SERVER STATE.

Jonathan Kehayias One Orange Chip Points: 26778 More actions · Answer 3

For those interested, you can use the same method to give SA rights or access like VIEW SERVER STATE to users with no access. For example to call sys.dm_exec_sql_text() as originally requested:

USE [master]

GO

CREATE DATABASE SAPermsTest

GO

CREATE LOGIN [PermsTestLogin]

WITH PASSWORD=N'c0mpl3xp@$$'

GO

USE [SAPermsTest]

GO

CREATE USER [PermsTestLogin] FROM LOGIN [PermsTestLogin]

GO

CREATE TABLE PermsTest

(RowID int identity primary key)

GO

GRANT INSERT ON PermsTest TO PermsTestLogin

GO

CREATE TRIGGER Audit_PermsTest

ON PermsTest

WITH EXECUTE AS OWNER

FOR INSERT, UPDATE, DELETE

AS

BEGIN

DECLARE @TEMP TABLE

(EventType nvarchar(30), Parameters int, EventInfo nvarchar(4000))

INSERT INTO @TEMP EXEC('DBCC INPUTBUFFER(@@SPID)')

SELECT EventInfo FROM @TEMP

SELECT SYSTEM_USER

SELECT text

FROM sys.dm_exec_requests

CROSS APPLY sys.dm_exec_sql_text(sql_handle)

WHERE session_id = @@SPID

END

GO

-- Test the trigger will fail. Make sure to revert

EXECUTE AS LOGIN='PermsTestLogin'

INSERT INTO PermsTest default values;

REVERT

GO

-- Revert Fails when trigger execution fails so do it now.

REVERT

GO

-- Create a certificate to sign stored procedures with

CREATE CERTIFICATE [SAPermsCertificate]

ENCRYPTION BY PASSWORD = '$tr0ngp@$$w0rd'

WITH SUBJECT = 'Certificate for signing Audit Triggers';

GO

-- Backup certificate so it can be create in master database

BACKUP CERTIFICATE [SAPermsCertificate]

TO FILE = 'D:\SQLBackups\SAPermsCertificate.CER';

GO

-- Add Certificate to Master Database

USE [master]

GO

CREATE CERTIFICATE [SAPermsCertificate]

FROM FILE = 'D:\SQLBackups\SAPermsCertificate.CER';

GO

-- Create a login from the certificate

CREATE LOGIN [SAPermsLogin]

FROM CERTIFICATE [SAPermsCertificate];

GO

-- The Login must have Authenticate Sever to access server scoped system tables

-- per http://msdn.microsoft.com/en-us/library/ms190785.aspx

GRANT AUTHENTICATE SERVER TO [SAPermsLogin]

GO

-- Add the VIEW Server State permission to the Certificate login.

GRANT VIEW SERVER STATE TO [SAPermsLogin]

GO

USE [SAPermsTest]

GO

-- Sign the procedure with the certificate's private key

ADD SIGNATURE TO OBJECT::Audit_PermsTest

BY CERTIFICATE [SAPermsCertificate]

WITH PASSWORD = '$tr0ngp@$$w0rd';

GO

-- Retest the Trigger function and it will work returning

-- CREATE TRIGGER statement for the sys.dm_exec_sql_text()

EXECUTE AS LOGIN='PermsTestLogin'

INSERT INTO PermsTest default values;

REVERT

GO

-- Cleanup

/*

USE [master]

GO

DROP LOGIN [SAPermsLogin]

DROP CERTIFICATE [SAPermsCertificate]

DROP DATABASE [SAPermsTest]

-- Delete the certificate backup from disk

*/

If you run the above, you will note that as I stated in my last response the sys.dm_exec_sql_text() DMF will not output the last statement called by the client it will output the last statement executed by the session which happens to be the execution of the trigger itself. Kind of self defeating code, at least in my opinion which is why I still fall back on good ole' trusty DBCC INPUTBUFFER to get the last input statement from the client.

FreeHansje SSChampion Points: 11751 More actions · Answer 4

Tnx Jonathan, this is really hel;pful, in several ways.

Greetz,
Hans Brouwer

FreeHansje SSChampion Points: 11751 More actions · Answer 5

Jonathan,

I wish to say thanks again. I must have done something wrong, different then you describe in your solution. I could have sworn I used the same construction to test permission on the DMV's, but could not get it working. But as I said, I must have donw something different, and since there is no1 at my current position with the knowledge to talk this over I could not pinpoint the error.

Also tnx for showing that my initial 'solution' did not work. With your suggestion I can get things working.

Tnx again, I have learned a lot today.

Greetz,
Hans Brouwer

ChiragNS One Orange Chip Points: 26137 More actions · Answer 6

Great article and here comes another dumb question!

After signing the procedure with certificate can the procedure be executed only by the login/user created from the certificate? Can other users execute the procedure.

"Keep Trying"

ChiragNS One Orange Chip Points: 26137 More actions · Answer 7

ChiragNS

One Orange Chip

Points: 26137

January 22, 2010 at 5:33 am

#1107254

Hi anyone there!!

"Keep Trying"

Jonathan Kehayias One Orange Chip Points: 26778 More actions · Answer 8

ChiragNS (1/18/2010)
Great article and here comes another dumb question!
After signing the procedure with certificate can the procedure be executed only by the login/user created from the certificate? Can other users execute the procedure.

No, you can GRANT EXECUTE on the stored procedure that is signed by the certificate to any database user. That's the point behind using the certificate signed stored procedure to grant access. The users don't have to have elevated rights, they only need the ability to EXECUTE the signed stored procedure, or a parent procedure in the ownership chain.

Jonathan Kehayias One Orange Chip Points: 26778 More actions · Answer 9

FreeHansje (1/18/2010)
Jonathan,
I wish to say thanks again. I must have done something wrong, different then you describe in your solution. I could have sworn I used the same construction to test permission on the DMV's, but could not get it working. But as I said, I must have donw something different, and since there is no1 at my current position with the knowledge to talk this over I could not pinpoint the error.
Also tnx for showing that my initial 'solution' did not work. With your suggestion I can get things working.
Tnx again, I have learned a lot today.

Did you figure your problem out? If not, DM me or shoot me a contact through my blog on SQLBlog and I'll see if I can help you troubleshoot the issue further.

ChiragNS One Orange Chip Points: 26137 More actions · Answer 10

Jonathan Kehayias (1/22/2010)
ChiragNS (1/18/2010)
Great article and here comes another dumb question!
After signing the procedure with certificate can the procedure be executed only by the login/user created from the certificate? Can other users execute the procedure.
No, you can GRANT EXECUTE on the stored procedure that is signed by the certificate to any database user. That's the point behind using the certificate signed stored procedure to grant access. The users don't have to have elevated rights, they only need the ability to EXECUTE the signed stored procedure, or a parent procedure in the ownership chain.

Thank you.

"Keep Trying"

Rachel Byford Hall of Fame Points: 3437 More actions · Answer 11

Brilliant article.

Only one thing which is a bit of a shame - this only works if the SP is execute as owner, not if it's execute as caller.

As a result, if you look in msdb.dbo.sysmail_allitems, all items sent with this method say they were sent by sa. Also it's allowed to send using private profiles to which nobody has been granted access.

If you send the mail by adding the user to the msdb role instead, then msdb.dbo.sysmail_allitems details the correct sender.

DatabaseMail is great, but the permissions are a real struggle. In addition to the sp_send_dbmail permission problem, it's hard to get the permissions sorted out for private profiles. All the documentation says that you can grant permissions on private profiles to database roles in msdb, but in actual fact it won't let you do this.

Rachel.

FreeHansje SSChampion Points: 11751 More actions · Answer 12

Another question, I'm stupified by the following:

I wish to allow non-sa users to run a bcp string with xp_cmdshell. The option to use this XP is by default turned off. I can get these non-sa users to run the xp_cmdshell, it's the turning on and off of the configuration which I cannot resolve.

What I'm looking at is a SP like this:

CREATE PROCEDURE testSP1

BEGIN

EXEC SP_CONFIGURE 'xp_cmdshell', 1;

RECONFIGURE WITH OVERRIDE;

EXEC XP_CMDSHELL 'DIR c:\' -- some VBCP command, but for a simple example...

EXEC SP_CONFIGURE 'xp_cmdshell', 0;

RECONFIGURE WITH OVERRIDE;

END

GO

I have tried constructions with EXECUTE AS and Certificates, but sofar nada. Scoured the Internet, no example specifically on permissions on SP_CONFIGURE.

Any suggestions?

Greetz,
Hans Brouwer

sam bryant Right there with Babe Points: 792 More actions · Answer 13

I have created a stored procedure in the msdb that will basically start a job and wait for completion. I have implemented the certificate signed stored procedure in one database successfully, but would now like to incorporate it into a second database. I was thinking I would be able to use the same certificate to make this happen (create in second database from file).

This does not seem to be the case though. Doing a select on sys.certificates in the second database shows NA for pvt_key_encryption_type and NO_PRIVATE_KEY for pvt_key_encryption_type_desc. I receive the following error when trying to sign the stored procedure in the second database from this certificate

Msg 15556, Level 16, State 1, Line 1

Cannot decrypt or encrypt using the specified certificate, either because it has no private key or because the password provided for the private key is incorrect.

I was wondering if this is possible. And if so if there are any reasons not to do this.

I could see this expanding to other databases in the future and would like to use one certificate (since everything will be targeting the same stored procedure in the msdb database) instead of having to create numerous certificates, logins, users, etc.

Any advise/information is much appreciated.

Thanks,

Sam

Jonathan Kehayias One Orange Chip Points: 26778 More actions · Answer 14

ssb-402814 (3/30/2011)
I have created a stored procedure in the msdb that will basically start a job and wait for completion. I have implemented the certificate signed stored procedure in one database successfully, but would now like to incorporate it into a second database. I was thinking I would be able to use the same certificate to make this happen (create in second database from file).
This does not seem to be the case though. Doing a select on sys.certificates in the second database shows NA for pvt_key_encryption_type and NO_PRIVATE_KEY for pvt_key_encryption_type_desc. I receive the following error when trying to sign the stored procedure in the second database from this certificate
Msg 15556, Level 16, State 1, Line 1
Cannot decrypt or encrypt using the specified certificate, either because it has no private key or because the password provided for the private key is incorrect.
I was wondering if this is possible. And if so if there are any reasons not to do this.
I could see this expanding to other databases in the future and would like to use one certificate (since everything will be targeting the same stored procedure in the msdb database) instead of having to create numerous certificates, logins, users, etc.
Any advise/information is much appreciated.
Thanks,
Sam

Sam,

While you and I have passed emails to resolve the problem, I wanted to post an update here in the comments as well so that anyone else encountering this issue has the reference to how to resolve it. I posted a blog post that details the problem with a repro and then shows how to fix the issue by backing up the private key for the certificate when the certificate is backed up so that the private key can be created with the certificate from the backup files in the new database.

Certificate Signing Stored Procedures in Multiple Databases

Bob hopw SSC Journeyman Points: 90 More actions · Answer 15

Excellent article.

I was having a permission denied on db_mail when sending a email from a sp that was being executed by Service Broker, and this was despite the user who was was executing existing in msdb.DatabaseMailUserRole and set trustworthy was on.

Ran through the article, created the certificate and assigned it .... success.

ty

Murtagh