CAPEC 7

Blind SQL Injection

Attack Pattern ID: 7 (Detailed Attack Pattern Completeness: Complete)

Typical Severity: High

Status: Draft

Description

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 attacker constructs input strings that probe the target through simple Boolean SQL expressions. The attacker can determine if the syntax and structure of the injection was successful based on whether the query was executed or not. Applied iteratively, the attacker determines how and where the target is vulnerable to SQL Injection.

For example, an attacker may try entering something like "username' AND 1=1; --" in an input field. If the result is the same as when the attacker entered "username" in the field, then the attacker knows that the application is vulnerable to SQL Injection. The attacker can then ask yes/no questions from the database server to extract information from it. For example, the attacker 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 attacker 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 attacker 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 attacker can determine all table names in the database. Subsequently, the attacker may execute an actual attack and send something like:

"username'; DROP TABLE trades; --

Attack Execution Flow

Explore

Hypothesize SQL queries in application:
Generated hypotheses regarding the SQL queries in an application. For example, the attacker may hypothesize that his input is passed directly into a query that looks like:
"SELECT * FROM orders WHERE ordernum = _____"
or
"SELECT * FROM orders WHERE ordernum IN (_____)"
or
"SELECT * FROM orders WHERE ordernum in (_____) ORDER BY _____"
Of course, there are many other possibilities.
Attack Step Techniques
ID Attack Step Technique Description Environments
1
Research types of SQL queries and determine which ones could be used at various places in an application.
env-All

ID	Attack Step Technique Description	Environments
1	Research types of SQL queries and determine which ones could be used at various places in an application.	env-All

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:

"5' OR 1=1; --"

and

"5) OR 1=1; --"

and

"ordernum DESC; --"

Attack Step Techniques

ID	Attack Step Technique Description	Environments
1	Add clauses to the SQL queries such that the query logic does not change.	env-All
2	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.	env-All

Outcomes

ID	type	Outcome Description
1	Success	At least one way to complete a hypothesized SQL query that would violate the application developer's assumptions.

Experiment

Determine user-controllable input susceptible to injection:

Determine the user-controllable input susceptible to injection. For each user-controllable input that the attacker suspects is vulnerable to SQL injection, attempt to inject the values determined in the previous step. If an error does not occur, then the attacker knows that the SQL injection was successful.

Attack Step Techniques

ID	Attack Step Technique Description	Environments
1	Use web browser to inject input through text fields or through HTTP GET parameters.	env-Web
2	Use a web application debugging tool such as Tamper Data, TamperIE, WebScarab,etc. to modify HTTP POST parameters, hidden fields, non-freeform fields, etc.	env-Web
3	Use network-level packet injection tools such as netcat to inject input	env-Web env-ClientServer env-Peer2Peer env-CommProtocol
4	Use modified client (modified by reverse engineering) to inject input.	env-ClientServer env-Peer2Peer env-CommProtocol

Indicators

ID	type	Indicator Description	Environments
1	Positive	Attacker receives normal response from server.	env-Web env-ClientServer env-Peer2Peer env-CommProtocol
2	Positive	Response takes expected amount of time after delay is injected.	env-Web env-ClientServer env-Peer2Peer env-CommProtocol
3	Negative	Server sends a specific error message that indicates programmatic parsing of the input data (e.g. NumberFormatException)	env-Web env-ClientServer env-Peer2Peer env-CommProtocol

Outcomes

ID	type	Outcome Description
1	Success	At least one user-controllable input susceptible to injection found.
2	Failure	No user-controllable input susceptible to injection found.

Security Controls

ID	type	Security Control Description
1	Detective	Unusual queries such as the ones described in the previous step, in application logs. Log files may contain unusual messages such as "User bob' OR 1=1; -- logged in". Operators should be alerted when such SQL commands appear in the logs.
2	Preventative	Input validation of user-controlled data before including it in a SQL query
3	Preventative	Use APIs that help mitigate SQL injection (such as PreparedStatement in Java)

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

Attack Step Techniques

ID	Attack Step Technique Description	Environments
1	Try injecting a string containing char(0x31)=char(0x31) (this evaluates to 1=1 in SQL Server only)	env-Web env-ClientServer env-Peer2Peer env-CommProtocol
2	Try injecting a string containing 0x313D31 (this evaluates to 1=1 in MySQL only)	env-Web env-ClientServer env-Peer2Peer env-CommProtocol
3	SecurityDatabase\Alert\Inject other database-specific commands into input fields susceptible to SQL Injection. The attacker can determine the type of database that is running by checking whether the query executed successfully or not (i.e. wheter the attacker received a normal response from the server or not).	env-Web env-ClientServer env-Peer2Peer env-CommProtocol

Indicators

ID	type	Indicator Description	Environments
1	Positive	Success outcome in previous step	env-Web env-ClientServer env-Peer2Peer env-CommProtocol
2	Negative	Failure outcome in previous step	env-Web env-ClientServer env-Peer2Peer env-CommProtocol

Outcomes

ID	type	Outcome Description
1	Success	Database platform in use discovered.
2	Failure	Database platform in use not discovered.

Exploit

Extract information about database schema:

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

Attack Step Techniques

ID	Attack Step Technique Description	Environments
1	Automatically extract database schema using a tool such as Absinthe.	env-Web
2	Manually perform the blind SQL Injection to extract desired information about the database schema.	env-Web env-ClientServer env-Peer2Peer env-CommProtocol

Indicators

ID	type	Indicator Description	Environments
1	Positive	Success outcome in previous step.	env-Web env-ClientServer env-Peer2Peer env-CommProtocol
2	Negative	Failure outcome in previous step.	env-Web env-ClientServer env-Peer2Peer env-CommProtocol

Outcomes

ID	type	Outcome Description
1	Success	Desired information about database schema extracted.
2	Failure	Desired information about database schema could not be extracted.

Security Controls

ID	type	Security Control Description
1	Detective	Large number of unusual queries in database logs.

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

Attack Step Techniques

ID	Attack Step Technique Description	Environments
1	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.	env-Web env-ClientServer env-Peer2Peer env-CommProtocol

Indicators

ID	type	Indicator Description	Environments
1	Positive	Success outcome in previous step.	env-Web env-ClientServer env-Peer2Peer env-CommProtocol
2	Negative	Failure outcome in previous step.	env-Web env-ClientServer env-Peer2Peer env-CommProtocol

Outcomes

ID	type	Outcome Description
1	Success	Attacker achieves goal of unauthorized system access, denial of service, etc.
2	Failure	Attacker cannot exploit the information gathered by blind SQL Injection

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 Likelihood of Exploit

Likelihood: High

Methods of Attack

Injection
Analysis

Examples-Instances

Description

In the PHP application TimeSheet 1.1, an attacker can successfully retrieve username and password hashes from the database using Blind SQL Injection. If the attacker is aware of the local path structure, the attacker 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

CVE-2006-4705

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

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

Data Modification
Information Leakage
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 attacker modifies the boolean condition each time to gain information from the database.

Related Weaknesses

CWE-ID	Weakness Name	Weakness Relationship Type
89	Improper Sanitization of Special Elements used in an SQL Command ('SQL Injection')	Targeted
209	Information Exposure Through an Error Message	Targeted
74	Failure to Sanitize Data into a Different Plane ('Injection')	Secondary
20	Improper Input Validation	Secondary
390	Detection of Error Condition Without Action	Secondary
697	Insufficient Comparison	Secondary
713	OWASP Top Ten 2007 Category A2 - Injection Flaws	Secondary
707	Improper Enforcement of Message or Data Structure	Secondary

Related Attack Patterns

Nature	Type	ID	Name	View(s) this relationship pertains to $View$s$$
CanPrecede	Attack Pattern	66	SQL Injection	Mechanism of Attack1000
ChildOf	Attack Pattern	66	SQL Injection	Mechanism of Attack (primary)1000
ParentOf	Attack Pattern	110	SQL Injection through SOAP Parameter Tampering	Mechanism of Attack (primary)1000

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.

Related Security Principles

Reluctance to Trust
Failing Securely
Defense in Depth

Related Guidelines

Never Use Input as Part of a Directive to any Internal Component
Handle All Errors Safely

Purposes

Penetration

CIA Impact

Confidentiality Impact: HighIntegrity Impact: HighAvailability Impact: High

Technical Context

Architectural Paradigms	All
Frameworks	All
Platforms	All
Languages	All

References

CWE - Input Validation

CWE - Improper Error Handling

Content History

Submissions
Submitter	Date	Comments
Chiradeep B Chhaya	2007-02-22	Third Draft - Revised to schema v1.4

Modifications
Modifier	Organization	Date	Comments
Malik Hamro	Cigital, Inc	2007-02-27	Reformat to new schema and review
Sean Barnum	Cigital, Inc	2007-03-05	Review and revise
Richard Struse	VOXEM, Inc	2007-03-26	Review and feedback leading to changes in Description, Attack Prerequisites and Related Attack Patterns
Sean Barnum	Cigital, Inc	2007-04-13	Modified pattern content according to review and feedback
Amit Sethi	Cigital, Inc.	2007-10-29	Added extended Attack Execution Flow

CAPEC 7

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