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  1. MariaDB Server
  2. MDEV-35563

Users without any permissions could retrieve table names via the error message of DROP TRIGGER

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      Users without any permissions can retrieve table names via the error message of the DROP TRIGGER statement.
      For example, if the table `test.tbl` has a trigger named `before_insert_tbl`, a user without any permissions can retrieve the table name by executing the statement `DROP TRIGGER test.before_insert_tbl`.
      The error message displayed is "ERROR 1142 (42000): TRIGGER command denied to user 'foo'@'localhost' for table 'tbl'", which reveals the table name `tbl` to the user.

      The Proof of Concept (PoC):

      -- Use the root user to connect to MariaDB and create a trigger and an empty user
      		 
      -- Example:
      		 
      --   docker run -itd --name some-mariadb --env MARIADB_ALLOW_EMPTY_ROOT_PASSWORD=1 -p 3306:3306 mariadb:11.7.1-rc
      		 
      --   docker exec -it some-mariadb mariadb -uroot
      		 
       
      		 
      CREATE DATABASE test;
      		 
      CREATE TABLE test.tbl (x INT);
      		 
      CREATE TRIGGER test.before_insert_tbl -- Create a trigger
      		 
      BEFORE INSERT ON test.tbl FOR EACH ROW
      		 
      INSERT INTO test SELECT 1;
      		 
      CREATE USER foo; -- Create an empty user
      		 
      QUIT; -- Exit
      		 
       
      		 
      -- Login with the user `foo` and try to drop trigger
      		 
      -- Example:
      		 
      --   docker exec -it some-mariadb mariadb -ufoo
      		 
       
      		 
      DROP TRIGGER test.test; -- Drop a non-existing trigger
      		 
      -- Error message: ERROR 1360 (HY000): Trigger does not exist
      		 
      DROP TRIGGER test.before_insert_tbl; -- Drop an existing trigger
      		 
      -- ERROR 1142 (42000): TRIGGER command denied to user 'foo'@'localhost' for table `test`.`tbl`

      From the error message when dropping an existing trigger, the user `foo` (who has no permissions) can infer the existence of the database `test`, the table `test.tbl`, and the trigger `test.before_insert_tbl`.

      If the user can "guess" a trigger name (e.g., via brute-force enumeration or by attempting commonly-used names) and the trigger name exists, the user can infer the existence of the trigger and retrieve the corresponding table name via the `DROP TRIGGER` statement.

      Since the user has no permissions, it seems unreasonable that they can obtain information about databases, tables, and triggers. Maybe it is a bug or issue?

      Instead, other statements like the DROP INDEX statement can protect such information:

      # Create index with the root user
      		 
      CREATE INDEX w ON test.tbl(x);
      		 
      QUIT; -- Exit
      		 
       
      		 
      # Connect with the empty user
      		 
      # Example:
      		 
      #   docker exec -it some-mariadb mariadb -ufoo
      		 
      # Attempting DROP INDEX
      		 
      DROP INDEX w ON test.tbl;
      		 
      -- ERROR 1142 (42000): INDEX command denied to user 'foo'@'localhost' for table `test`.`tbl`
      		 
      DROP INDEX w ON testx.tbl;
      		 
      -- ERROR 1142 (42000): INDEX command denied to user 'foo'@'localhost' for table `testx`.`tbl`
      		 
      DROP INDEX w ON `???`.tbl;
      		 
      -- ERROR 1142 (42000): INDEX command denied to user 'foo'@'localhost' for table `???`.`tbl`
      		 
      DROP INDEX w ON `???`.`???`;
      		 
      -- ERROR 1142 (42000): INDEX command denied to user 'foo'@'localhost' for table `???`.`???`
      		 
      DROP INDEX w ON `test`.`???`;
      		 
      -- ERROR 1142 (42000): INDEX command denied to user 'foo'@'localhost' for table `test`.`???`
      		 
      DROP INDEX `???` ON testx.tbl;
      		 
      -- ERROR 1142 (42000): INDEX command denied to user 'foo'@'localhost' for table `test`.`tbl`

      For the `DROP INDEX` statement, the user without permissions cannot retrieve any information about the database, table, or index because the error messages are always generic. This seems to be the correct behavior for `DROP` statements.

      So, maybe the current error message of DROP TRIGGER needs to be improved?

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            sanja Oleksandr Byelkin
            fuboat Jingzhou Fu
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