{"id":2055,"date":"2014-02-15T11:00:33","date_gmt":"2014-02-15T16:00:33","guid":{"rendered":"http:\/\/sqlity.net\/en\/?p=2055"},"modified":"2014-11-13T13:16:37","modified_gmt":"2014-11-13T18:16:37","slug":"undoing-a-deny","status":"publish","type":"post","link":"https:\/\/sqlity.net\/en\/2055\/undoing-a-deny\/","title":{"rendered":"How to undo a DENY"},"content":{"rendered":"
\n

Introduction<\/h3>\n

\nYesterday I showed you that a DENY<\/span> is durable<\/a>, meaning a DENY<\/span> gets persisted by SQL Server the same way a GRANT<\/span> does. If you have used the DENY<\/span> statement before, or maybe while reading yesterday's post, you might have had the question what you can do if you change your mind on a DENY<\/span> and what to undo it now.\n<\/p>\n

Undoing a DENY<\/h3>\n

\nOne way to deal with this is to just GRANT<\/span> the same permission, as successive GRANT<\/span> and DENY<\/span> statements overwrite each other. However that might have other side effects down the road that you do not want, especially if you are dealing with roles.\n<\/p>\n

\nYou could go and REVOKE<\/span> the GRANT<\/span> after you used it to overwrite the DENY<\/span>. However, there is a much simpler way. I said yesterday that a DENY<\/span> is stored in the same permissions list that a GRANT<\/span> would be stored in. The only difference between the two is actually just a \"state\" value on the entry, that is either \"G\" for GRANT<\/span> or \"D\" for DENY<\/span>. That means that you can REVOKE<\/span> a DENY<\/span> the same way you REVOKE<\/span> a GRANT<\/span>.\n<\/p>\n

\nSo far you might have had the impression that a REVOKE<\/span> always reduces permissions. But that is not actually accurate. Instead, the REVOKE<\/span> statement removes an entry from SQL Server's internal permissions list, no matter if that entry was a GRANT<\/span> or a DENY<\/span>. So after executing a REVOKE<\/span> the target principal might just have more permissions than before.\n<\/p>\n

REVOKE a DENY<\/h3>\n

\nLet's look at an example. First I am going to create our schema, table and user that we have become accustomed to over the last few posts:\n<\/p>\n

\n[sql]\nCREATE LOGIN TestLogin1 WITH PASSWORD='********', CHECK_POLICY = OFF;
\nCREATE USER TestUser1 FOR LOGIN TestLogin1;
\nGO
\nCREATE SCHEMA TestSchema1;
\nGO
\nCREATE TABLE TestSchema1.tst(id INT);
\nINSERT INTO TestSchema1.tst VALUES(42);
\n[\/sql]\n<\/div>\n

\nNow we can use a DENY SELECT<\/span> on the schema to override a GRANT SELECT<\/span> on the table:\n<\/p>\n

\n\"DENY<\/a>\n<\/p>\n

\nSo far this is not surprising. Now let's see what happens if we REVOKE SELECT<\/span> on the schema from our user:\n<\/p>\n

\n\"REVOKE<\/a>\n<\/p>\n

\nBecause the REVOKE<\/span> removed the existing DENY<\/span>, TestUser1<\/span> can now access the table.\n<\/p>\n

\n- Let that sink in for a second. -\n<\/p>\n

\nThe REVOKE<\/span> actually increased the active permissions for TestUser1<\/span> as it removed the preexisting DENY<\/span>. Also, there is no way to tell just by looking at the REVOKE<\/span> statement itself. The syntax to remove a granted permission is exactly the same as the syntax to remove a denied permission.\n<\/p>\n

\nWhen revoking permissions you need to therefore always pay attention to actually revoking the intended permission. Just executing a REVOKE<\/span> might otherwise have the totally opposite effect of what you were looking for.\n<\/p>\n

Summary<\/h3>\n

\nThe REVOKE<\/span> statement can be used to remove not only prior grants but also prior denies. That means that executing a REVOKE<\/span> statement can effectively increase the active permissions.\n<\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"

Undoing a DENY that has become obsolete is actually quite simple. Read on to see how you can remove a DENY the same way you would remove a GRANT.<\/p>\n

[more…]<\/a><\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[5,34],"tags":[],"class_list":["post-2055","post","type-post","status-publish","format-standard","hentry","category-general","category-security"],"acf":[],"yoast_head":"\nHow to undo a DENY - sqlity.net<\/title>\n<meta name=\"description\" content=\"Undoing a DENY that has become obsolete is actually quite simple. 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