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CAPEC-7: Blind SQL Injection

Blind SQL Injection
Definition in a New Window Definition in a New Window
Attack Pattern ID: 7
Abstraction: Detailed
Status: Draft
Completeness: Complete
Presentation Filter:
+ Summary

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.

+ Attack Steps
  1. Hypothesize SQL queries in application: Generated hypotheses regarding the SQL queries in an application. For example, the adversary may hypothesize that his input is passed directly into a query that looks like:

    Research types of SQL queries and determine which ones could be used at various places in an application.

  2. Determine how to inject information into the queries: Determine how to inject information into the queries from the previous step such that the injection does not impact their logic. For example, the following are possible injections for those queries:

    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.

  1. 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.

    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.

  2. 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

    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).

  1. Extract information about database schema: Extract information about database schema by getting the database to answer yes/no questions about the schema.

    Automatically extract database schema using a tool such as Absinthe.

    Manually perform the blind SQL Injection to extract desired information about the database schema.

  2. 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

    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.

+ Attack 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.

+ Typical Severity


+ Typical Likelihood of Exploit

Likelihood: High

+ Methods of Attack
  • Injection
  • Analysis
+ Examples-Instances


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; --


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.

Related Vulnerabilities

+ Attacker Skills or Knowledge Required

Skill or Knowledge Level: 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.

+ Probing Techniques

In order to determine the right syntax for the query to inject, the attacker tries to determine the right number of parameters to the query and their types. This is achieved by formulating conditions that result in a true/false answer from the database. If the logical condition is true, the database will execute the rest of the query. If not, a custom error page or a default page is returned. Another approach is to ask such true/false questions of the database and note the response times to a query with a logically true condition and one with a false condition.

+ Indicators-Warnings of 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.

+ Solutions and Mitigations

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.

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.

+ Attack Motivation-Consequences
ScopeTechnical ImpactNote
Modify application data
Read application data
Execute unauthorized code or commands
Run Arbitrary Code
+ Injection Vector

User-controllable input to the application

+ Payload

SQL statements intended to bypass checks or retrieve information about the database

+ Activation Zone

Back-end database

+ Payload Activation Impact

The injected SQL statements are such that they result in a true/false query to the database. If the database evaluates a statement to be logically true, it responds with the requested data. If the condition is evaluated to be logically false, an error is returned. The adversary modifies the Boolean condition each time to gain information from the database.

+ Relevant Security Requirements

Custom error pages must be used to handle exceptions such that they do not reveal any information about the architecture of the application or the database.

Special characters in user-controllable input must be escaped before use by the application.

Employ application-level safeguards to filter data and handle exceptions gracefully.

+ Purposes
  • Penetration
+ CIA Impact
Confidentiality Impact: HighIntegrity Impact: HighAvailability Impact: High
+ Technical Context
Architectural Paradigms
+ References
[R.7.1] [REF-3] "Common Weakness Enumeration (CWE)". CWE-20 - Input Validation. Draft. The MITRE Corporation. 2007. <http://cwe.mitre.org/data/definitions/20.html>.
[R.7.2] [REF-3] "Common Weakness Enumeration (CWE)". CWE-390 - Improper Error Handling. Draft. The MITRE Corporation. 2007. <http://cwe.mitre.org/data/definitions/390.html>.
+ Content History
CAPEC Content TeamThe MITRE Corporation2014-06-23Internal_CAPEC_Team
CAPEC Content TeamThe MITRE Corporation2017-01-09Updated Related_Attack_PatternsInternal
CAPEC Content TeamThe MITRE Corporation2017-08-04Updated Attack_Phases, Description, Description Summary, Examples-Instances, Payload_Activation_Impact, Resources_RequiredInternal

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Page Last Updated or Reviewed: August 04, 2017