SQL Security

1. +
Housekeeping
Project/assignment 6/quiz 6 questions?
Quiz 6: Query optimization, database
security
 At 9:10, you’ll have 15 minutes to do on-
line student ratings
Office hours today: 10:30-12:30
Offce hours next week:
M/W/F 10:30-12:30

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Security:
Access Control, SQL Injection Attacks
Based upon slides from: classes.soe.ucsc.edu/.../SQL%20Injection%20Attacks.ppt
homes.cs.washington.edu/~suciu/current-trends.ppt
www.cse.iitb.ac.in/dbms/Data/.../DBSecurity-Overview.ppt

3. +
Data Security
Protection from malicious attempts to
steal (view) or modify data.
The science and study of methods of
protecting data (...) from unauthorized
disclosure and modification
Data Security = Confidentiality +
Integrity

4. + 4
Traditional Data Security
Security in statistical databases = Theory
 http://en.wikipedia.org/wiki/Statistical_database
 In a statistical database, it is often desired to allow
query access only to aggregate data, not individual
records. Securing such a database is a difficult
problem, since intelligent users can use a
combination of aggregate queries to derive
information about a single individual.
Security in SQL = Access control + Views

5. + 5
Access Control in SQL
GRANT privileges ON object TO users
[WITH GRANT OPTIONS]
privileges = SELECT | INSERT | DELETE | . . .
object = table | attribute
REVOKE privileges ON object FROM users
[CASCADE ]
[Griffith&Wade'76, Fagin'78]

6. +
Access Control in MySQL
 http://dev.mysql.com/doc/refman/5.0/en/privilege-system.html
 The primary function of the MySQL privilege system is to authenticate
a user who connects from a given host and to associate that user with
privileges on a database such as SELECT, INSERT, UPDATE, and
DELETE
 There are some things that you cannot do with the MySQL privilege
system:
 You cannot explicitly specify that a given user should be denied access. That
is, you cannot explicitly match a user and then refuse the connection.
 You cannot specify that a user has privileges to create or drop tables in a
database but not to create or drop the database itself.
 A password applies globally to an account. You cannot associate a password
with a specific object such as a database, table, or routine.

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Views in SQL
A SQL View = (almost) any SQL query
 Typically used as:
GRANT SELECT ON pmpStudents TO DavidRispoli
CREATE VIEW pmpStudents AS
SELECT * FROM Students WHERE…

8. +
Views in MySQL
 http://dev.mysql.com/doc/refman/5.0/en/create-view.html
 CREATE [OR REPLACE]
[ALGORITHM = {UNDEFINED | MERGE | TEMPTABLE}]
[DEFINER = { user | CURRENT_USER }]
[SQL SECURITY { DEFINER | INVOKER }]
VIEW view_name [(column_list)]
AS select_statement
[WITH [CASCADED | LOCAL] CHECK OPTION]
 The DEFINER and SQL SECURITY clauses determine which
MySQL account to use when checking access privileges for the
view when a statement is executed that references the view.

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Summary of SQL Security
Limitations:
 Often no row level access control
 Note: DB specific – fine-grained access control is an
active area of improvement
 Table creator owns the data (not always fair)
… or spectacular failure:
 Only ~30% assign privileges to users/roles
 And then to protect entire tables, not columns
Access control = great success story of the DB
community...

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MySQL security
 http://dev.mysql.com/doc/refman/5.0/en/security.html
Many aspects:
 General factors that affect security. These include
choosing good passwords, not granting unnecessary
privileges to users, ensuring application security by
preventing SQL injections and data corruption, and others.
See Section 6.1, “General Security Issues”.
 Security of the installation itself. The data files, log files,
and the all the application files of your installation should be
protected to ensure that they are not readable or writable by
unauthorized parties. For more information, see Section
2.18, “Postinstallation Setup and Testing”.

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MySQL security
 Access control and security within the database system itself,
including the users and databases granted with access to the
databases, views and stored programs in use within the database. For
more information, see Section 6.2, “The MySQL Access Privilege
System”, and Section 6.3, “MySQL User Account Management”.
 Network security of MySQL and your system. The security is related
to the grants for individual users, but you may also wish to restrict
MySQL so that it is available only locally on the MySQL server host, or
to a limited set of other hosts.
 Ensure that you have adequate and appropriate backups of your
database files, configuration and log files. Also be sure that you have a
recovery solution in place and test that you are able to successfully
recover the information from your backups. See Chapter 7, Backup
and Recovery.

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SQL Injection Attacks

13. +
http://www.circleid.com/posts/20130325_sql_injection_in
_the_wild/

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What is a SQL Injection Attack?
Many web applications take user input from
a form
Often this user input is used literally in the
construction of a SQL query submitted to a
database. For example:
 SELECT productdata FROM table WHERE
productname = ‘user input product name’;
A SQL injection attack involves placing SQL
statements in the user input

15. +
SQL Injection Attacks on the rise
 https://www.net-security.org/secworld.php?id=13313
 “Many, many sites have lost customer data in this way,” said
Chris Hinkley, Senior Security Engineer at FireHost. “SQL
Injection attacks are often automated and many website
owners may be blissfully unaware that their data could actively
be at risk. These attacks can be detected and businesses
should be taking basic and blanket steps to block attempted
SQL Injection, as well as the other types of attacks we
frequently see.”

16. +
2012 News of SQL attacks
 http://www.mysqlperformanceblog.com/2012/07/18/sql-injection-still-a-
problem/
 An SQL injection vulnerability resulted in an urgent June bugfix release
of Ruby on Rails 3.x.
 Yahoo! Voices was hacked in July. The attack acquired 453,000 user
email addresses and passwords. The perpetrators claimed to have
used union-based SQL injection to break in.
 LinkedIn.com leaked 6.5 million user credentials in June. A class action
lawsuit alleges that the attack was accomplished with SQL injection.
 SQL injection was documented as a security threat in 1998, but new
incidents still occur every month. Making honest mistakes, developers
fail to defend against this means of attack, and the security of online
data is at risk for all of us because of it.

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Some good sites to learn more
Prevention guide (with sample code in many languages):
http://bobby-tables.com/
Tutorials:
(webinar) http://www.percona.com/webinars/2012-07-25-sql-injection-myths-and-
fallacies
http://www.netrostar.com/SQL-Injection-Attack
http://www.unixwiz.net/techtips/sql-injection.html
Cool site that let’s you try out attacks on a sample DB and explains
why they work
http://sqlzoo.net/hack/
Research paper on how to retrofit existing websites to combat SQL
injection attacks
http://lersse-dl.ece.ubc.ca/record/205/files/paper.pdf

18. +
An Example SQL Injection Attack
Product Search:
 This input is put directly into the SQL statement within the
Web application:
 $query = “SELECT prodinfo FROM prodtable WHERE prodname =
‘” . $_POST[‘prod_search’] . “’”;
 Creates the following SQL:
 SELECT prodinfo FROM prodtable WHERE prodname = ‘blah‘ OR ‘x’
= ‘x’
 Attacker has now successfully caused the entire database to be
returned.
blah‘ OR ‘x’ = ‘x

19. +
A More Malicious Example
 What if the attacker had instead entered:
 blah‘; DROP TABLE prodinfo; --
 Results in the following SQL:
 SELECT prodinfo FROM prodtable WHERE prodname = ‘blah’; DROP TABLE
prodinfo; --’
 Note how comment (--) consumes the final quote
 Causes the entire database to be deleted
 Depends on knowledge of table name
 This is sometimes exposed to the user in debug code called during a
database error
 Use non-obvious table names, and never expose them to user
 Usually data destruction is not your worst fear, as there is low economic
motivation

20. +
Other injection possibilities
Using SQL injections, attackers can:
 Add new data to the database
 Could be embarrassing to find yourself selling
politically incorrect items on an eCommerce site
 Perform an INSERT in the injected SQL
 Modify data currently in the database
 Could be very costly to have an expensive item
suddenly be deeply ‘discounted’
 Perform an UPDATE in the injected SQL
 Often can gain access to other user’s system
capabilities by obtaining their password

21. +
Best defence
If possible, use bound variables with
prepared statements
 Many libraries allow you to bind inputs to variables
inside a SQL statement
 PERL example (from
http://www.unixwiz.net/techtips/sql-injection.html)
$sth = $dbh->prepare("SELECT email, userid FROM members
WHERE email = ?;");
$sth->execute($email);
See http://bobby-tables.com for example code in many
languages

22. +
How does this prevent an attack?
 The SQL statement you pass to prepare is parsed and
compiled by the database server.
 By specifying parameters (either a ? or a named parameter
like :name) you tell the database engine what to filter on.
 Then when you call execute the prepared statement is
combined with the parameter values you specify.
 It works because the parameter values are combined with
the compiled statement, not a SQL string.
 SQL injection works by tricking the script into including malicious
strings when it creates SQL to send to the database. So by sending
the actual SQL separately from the parameters you limit the risk of
ending up with something you didn't intend.

23. +
Other Defenses
Use provided functions for escaping strings
 Many attacks can be thwarted by simply using the SQL
string escaping mechanism
 ‘  ’ and “  ”
 mysql_real_escape_string() is the preferred function for
this
Will not guard against all attacks
 Consider:
 SELECT fields FROM table WHERE id = 23 OR 1=1
 No quotes here!

24. +
More Defenses
Check syntax of input for validity
 Many classes of input have fixed languages
 Email addresses, dates, part numbers, etc.
 Verify that the input is a valid string in the language
 Some languages allow problematic characters (e.g.,
‘*’ in email); may decide to not allow these
 Exclude quotes and semicolons
 Not always possible: consider the name Bill O’Reilly
 Want to allow the use of single quotes in names
Have length limits on input
 Many SQL injection attacks depend on entering long
strings

25. +
Even More Defenses
Scan query string for undesirable word
combinations that indicate SQL statements
 INSERT, DROP, etc.
 If you see these, can check against SQL syntax to see if
they represent a statement or valid user input
Limit database permissions and segregate users
 If you’re only reading the database, connect to database
as a user that only has read permissions
 Never connect as a database administrator in your web
application

26. +
And Yet More Defenses
 Configure database error reporting
 Default error reporting often gives away information
that is valuable for attackers (table name, field name,
etc.)
 Configure so that this information is never exposed to a
user