Learnitweb

A03:2021 – Injection

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by

Editorial Team
in

1. Overview

Injection vulnerabilities occur when an attacker sends malicious input into an application, causing it to execute unintended commands or access unauthorized data. This type of vulnerability is one of the most severe and prevalent in web applications and other software systems.

Injection attacks exploit the application’s failure to properly validate or sanitize user inputs. When user input is directly included in commands or queries to systems like databases, interpreters, or operating systems, attackers can manipulate the input to alter the execution flow.

2. Description

An application is vulnerable to attack when:

  • User-supplied data is not validated, filtered, or sanitized by the application.
  • Dynamic queries or non-parameterized calls without context-aware escaping are used directly in the interpreter.
  • Hostile data is used within object-relational mapping (ORM) search parameters to extract additional, sensitive records.
  • Hostile data is directly used or concatenated. The SQL or command contains the structure and malicious data in dynamic queries, commands, or stored procedures.

The concept is identical among all interpreters. Source code review is the best method of detecting if applications are vulnerable to injections. Automated testing of all parameters, headers, URL, cookies, JSON, SOAP, and XML data inputs is strongly encouraged.

3. How to Prevent

Preventing injection requires keeping data separate from commands and queries:

  • The preferred option is to use a safe API, which avoids using the interpreter entirely, provides a parameterized interface, or migrates to Object Relational Mapping Tools (ORMs).
    Note: Even when parameterized, stored procedures can still introduce SQL injection if PL/SQL or T-SQL concatenates queries and data or executes hostile data with EXECUTE IMMEDIATE or exec().
  • Use positive server-side input validation. This is not a complete defense as many applications require special characters, such as text areas or APIs for mobile applications.
  • For any residual dynamic queries, escape special characters using the specific escape syntax for that interpreter.
    Note: SQL structures such as table names, column names, and so on cannot be escaped, and thus user-supplied structure names are dangerous. This is a common issue in report-writing software.
  • Use LIMIT and other SQL controls within queries to prevent mass disclosure of records in case of SQL injection.

4. Example Attack Scenarios

Scenario #1: An application uses untrusted data in the construction of the following vulnerable SQL call:

String query = "SELECT \* FROM accounts WHERE custID='" + request.getParameter("id") + "'";

Scenario #2: Similarly, an application’s blind trust in frameworks may result in queries that are still vulnerable, (e.g., Hibernate Query Language (HQL)):

Query HQLQuery = session.createQuery("FROM accounts WHERE custID='" + request.getParameter("id") + "'");

In both cases, the attacker modifies the ‘id’ parameter value in their browser to send: ‘ UNION SLEEP(10);–. For example:

http://example.com/app/accountView?id=' UNION SELECT SLEEP(10);--

This changes the meaning of both queries to return all the records from the accounts table. More dangerous attacks could modify or delete data or even invoke stored procedures.