PostgreSQL Stacked Query

Context

This article explores the technique of exploiting PostgreSQL stacked queries for SQL injection attacks. Readers are expected to have a basic understanding of SQL syntax, how databases interact with applications, and the structure of HTTP requests. With this knowledge, you'll learn how to exploit PostgreSQL's handling of stacked queries to escalate privileges, inject unauthorized commands, or manipulate data.

Theory

Stacked Queries in SQL

Stacked queries are multiple SQL statements executed in a single request, separated by semicolons. This capability allows for the execution of several commands at once, which can be leveraged by attackers to bypass standard input validation measures. When properly leveraged, stacked queries can create substantial vulnerabilities if they are not carefully managed.

PostgreSQL Specific Syntax for Stacked Queries

PostgreSQL supports the execution of stacked queries using semicolons to separate each SQL statement. This feature can be misused when an application fails to validate or sanitize user inputs effectively, allowing the user to append additional queries that can be detrimental to the database's integrity.

Exploitation of Stacked Queries

The exploitation process involves injecting additional SQL commands that execute unauthorized actions against the database. This method takes advantage of protocol weaknesses, particularly the lack of sufficient input sanitization and validation, making it possible to perform operations such as data extraction, privilege escalation, or data manipulation.

Bypassing Security Measures with Stacked Queries

Attackers craft payloads that are designed to evade input filters and execute unwanted stacked queries. By carefully constructing the SQL injection to bypass basic security measures, attackers can exploit stacked queries to perform numerous harmful actions on the database.

Detection and Mitigation of Stacked Queries

To prevent such vulnerabilities, it is imperative to utilize parameterized queries in application code, which prevents the execution of unintended queries. Applications must enforce strict input validation to mitigate the risk of allowing stacked queries, thereby safeguarding the database from exploitation via improperly handled inputs.

Practice

Exploiting PostgreSQL Stacked Queries

To manually exploit PostgreSQL stacked queries, you can follow these steps:

• Escalate Privileges:

  Inject the following stacked query to escalate user privileges by modifying roles directly:

  SELECT * FROM users WHERE id=1; UPDATE users SET role='admin' WHERE id=1;
  

  This stacked query first retrieves information based on an assumed user ID, then escalates user privileges by updating their role to 'admin'.

• Inject Unauthorized Data:

  Send a payload to insert data into a log table:

  SELECT * FROM users WHERE id=1; INSERT INTO logs (message) VALUES ('injected');
  

  After executing a normal query, this payload injects a record into the logs table, potentially flooding it with unauthorized data.

• Destructive Actions:

  Use a query to drop a critical database table:

  SELECT * FROM users WHERE id=1; DROP TABLE users;
  

  This example first queries the users table, then maliciously drops it, causing data loss.

By executing these commands, multiple SQL operations can occur within a single database interaction, potentially altering the database's state catastrophically if not properly mitigated.

Tools

• sqlmap
• Burp Suite

These tools assist in automating and simulating SQL injection attacks, including those involving stacked queries, providing a practical offensive toolkit for further exploration of this vulnerability type.