Code injection

Code injection is the exploitation of a computer bug that is caused by processing invalid data. Injection is used by an attacker to introduce (or "inject") code into a vulnerable computer program and change the course of execution. The result of successful code injection is often disastrous (for instance: code injection is used by some computer worms to propagate).

Code injection vulnerabilities (injection flaws) occur when an application sends untrusted data to an interpreter. Injection flaws are most often found in SQL, LDAP, XPath, or NoSQL queries; OS commands; XML parsers, SMTP headers, program arguments, etc. Injection flaws tend to be easier to discover when examining source code than via testing. Scanners and fuzzers can help attackers find injection flaws.

Injection can result in data loss or corruption, lack of accountability, or denial of access. Injection can sometimes lead to complete host takeover.

Certain types of code injection are errors in interpretation, giving special meaning to mere user input. Similar interpretation errors exist outside the world of computer science such as the comedy routine Who's on First?. In the routine, there is a failure to distinguish proper names from regular words. Likewise, in some types of code injection, there is a failure to distinguish user input from system commands.

Code injection techniques are popular in system hacking or cracking to gain information, privilege escalation or unauthorized access to a system. Code injection can be used malevolently for many purposes, including:

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