COMMON ATTACK PATTERN ENUMERATION AND CLASSIFICATIONLive MITRE record
CAPEC-7
Blind SQL Injection
Blind SQL Injection results from an insufficient mitigation for SQL Injection. Although suppressing database error messages are considered best practice, the suppression alone is not sufficient to prevent SQL Injection. Blind SQL Injection is a form of SQL Injection that overcomes the lack of error messages. Without the error messages that facilitate SQL Injection, the adversary constructs input strings that probe the target through simple Boolean SQL expressions. The adversary can determine if the syntax and structure of the injection was successful based on whether the query was executed or not. Applied iteratively, the adversary determines how and where the target is vulnerable to SQL Injection.
Abstraction
Detailed
Typical severity
High
Likelihood of attack
High
Understand the attack
What is this attack pattern?
Blind SQL Injection results from an insufficient mitigation for SQL Injection. Although suppressing database error messages are considered best practice, the suppression alone is not sufficient to prevent SQL Injection. Blind SQL Injection is a form of SQL Injection that overcomes the lack of error messages. Without the error messages that facilitate SQL Injection, the adversary constructs input strings that probe the target through simple Boolean SQL expressions. The adversary can determine if the syntax and structure of the injection was successful based on whether the query was executed or not. Applied iteratively, the adversary determines how and where the target is vulnerable to SQL Injection.
Execution flow
How does the attack proceed, step by step?
Explore
Hypothesize SQL queries in application
Techniques used
- Research types of SQL queries and determine which ones could be used at various places in an application.
Determine how to inject information into the queries
Techniques used
- Add clauses to the SQL queries such that the query logic does not change.
- Add delays to the SQL queries in case server does not provide clear error messages (e.g. WAITFOR DELAY '0:0:10' in SQL Server or BENCHMARK(1000000000,MD5(1) in MySQL). If these can be injected into the queries, then the length of time that the server takes to respond reveals whether the query is injectable or not.
Experiment
Determine user-controllable input susceptible to injection
Determine the user-controllable input susceptible to injection. For each user-controllable input that the adversary suspects is vulnerable to SQL injection, attempt to inject the values determined in the previous step. If an error does not occur, then the adversary knows that the SQL injection was successful.
Techniques used
- Use web browser to inject input through text fields or through HTTP GET parameters.
- Use a web application debugging tool such as Tamper Data, TamperIE, WebScarab,etc. to modify HTTP POST parameters, hidden fields, non-freeform fields, etc.
- Use network-level packet injection tools such as netcat to inject input
- Use modified client (modified by reverse engineering) to inject input.
Determine database type
Determines the type of the database, such as MS SQL Server or Oracle or MySQL, using logical conditions as part of the injected queries
Techniques used
- Try injecting a string containing char(0x31)=char(0x31) (this evaluates to 1=1 in SQL Server only)
- Try injecting a string containing 0x313D31 (this evaluates to 1=1 in MySQL only)
- Inject other database-specific commands into input fields susceptible to SQL Injection. The adversary can determine the type of database that is running by checking whether the query executed successfully or not (i.e. whether the adversary received a normal response from the server or not).
Exploit
Extract information about database schema
Extract information about database schema by getting the database to answer yes/no questions about the schema.
Techniques used
- Automatically extract database schema using a tool such as Absinthe.
- Manually perform the blind SQL Injection to extract desired information about the database schema.
Exploit SQL Injection vulnerability
Use the information obtained in the previous steps to successfully inject the database in order to bypass checks or modify, add, retrieve or delete data from the database
Techniques used
- Use information about how to inject commands into SQL queries as well as information about the database schema to execute attacks such as dropping tables, inserting records, etc.
Requirements
What does the attack require?
Prerequisites
- SQL queries used by the application to store, retrieve or modify data.
- User-controllable input that is not properly validated by the application as part of SQL queries.
Skills required
- Medium: Determining the database type and version, as well as the right number and type of parameters to the query being injected in the absence of error messages requires greater skill than reverse-engineering database error messages.
Resources required
- None: No specialized resources are required to execute this type of attack.
Detection
What are the indicators of the attack?
The only indicators of successful Blind SQL Injection are the application or database logs that show similar queries with slightly differing logical conditions that increase in complexity over time. However, this requires extensive logging as well as knowledge of the queries that can be used to perform such injection and return meaningful information from the database.
Impact
What does a successful attack lead to?
Modify Data
Affected scopes: Integrity
Read Data
Affected scopes: Confidentiality
Execute Unauthorized Commands
Affected scopes: Confidentiality, Integrity, Availability
Defence
How is it prevented and mitigated?
1
Security by Obscurity is not a solution to preventing SQL Injection. Rather than suppress error messages and exceptions, the application must handle them gracefully, returning either a custom error page or redirecting the user to a default page, without revealing any information about the database or the application internals.
2
Strong input validation - All user-controllable input must be validated and filtered for illegal characters as well as SQL content. Keywords such as UNION, SELECT or INSERT must be filtered in addition to characters such as a single-quote(') or SQL-comments (--) based on the context in which they appear.
Real world
MITRE example instances
Example instance 1Detail
An adversary may try entering something like "username' AND 1=1; --" in an input field. If the result is the same as when the adversary entered "username" in the field, then the adversary knows that the application is vulnerable to SQL Injection. The adversary can then ask yes/no questions from the database server to extract information from it. For example, the adversary can extract table names from a database using the following types of queries:
"username' AND ascii(lower(substring((SELECT TOP 1 name FROM sysobjects WHERE xtype='U'), 1, 1))) > 108".
If the above query executes properly, then the adversary knows that the first character in a table name in the database is a letter between m and z. If it doesn't, then the adversary knows that the character must be between a and l (assuming of course that table names only contain alphabetic characters). By performing a binary search on all character positions, the adversary can determine all table names in the database. Subsequently, the adversary may execute an actual attack and send something like:
"username'; DROP TABLE trades; --
Example instance 2Detail
In the PHP application TimeSheet 1.1, an adversary can successfully retrieve username and password hashes from the database using Blind SQL Injection. If the adversary is aware of the local path structure, the adversary can also remotely execute arbitrary code and write the output of the injected queries to the local path. Blind SQL Injection is possible since the application does not properly sanitize the $_POST['username'] variable in the login.php file. See also: CVE-2006-4705