CRLF (%0D%0A) Injection

👉 Overview

👀 What ?

CRLF Injection, or Carriage Return Line Feed Injection, is a type of security vulnerability that occurs when an attacker injects the CRLF characters into an application, which can lead to a range of harmful effects such as data theft, code execution, or even denial of service.

🧐 Why ?

Understanding CRLF Injection is important because it is a common vulnerability that can be exploited in numerous ways, potentially leading to serious security breaches. For instance, it can be used to split HTTP responses, manipulate web content, or even steal sensitive data.

⛏️ How ?

Typically, CRLF Injection is carried out by inserting the %0D%0A sequence into user input fields, which is then processed by the application. To prevent this, developers should ensure that their applications properly validate and sanitize all user inputs. Additionally, they should use secure coding practices and regularly review their code for potential vulnerabilities.

⏳ When ?

CRLF Injection attacks have been known ever since the early days of the internet, as it is intrinsically linked to the way HTTP protocol works. However, they have become increasingly prevalent with the rise of web applications in the past couple of decades.

⚙️ Technical Explanations

CRLF stands for Carriage Return (ASCII 13, or %0D in hexadecimal) and Line Feed (ASCII 10, or %0A in hexadecimal). These are control characters used to mark a new line. If an attacker can inject these characters into an application, they can trick the application into thinking that a new line has started, and potentially inject malicious content into the application's output. This can lead to a wide range of security issues, from data theft to code execution.