What is CRLF Injection? Attacks you can perform with it?

CRLF Injection - Securium solutions

Feb 23, 2023 / By Securium solutions

What is CRLF Injection?

CRLF Injection is a type of web application vulnerability that occurs when user input is not properly validated or sanitized. The term CRLF stands for Carriage Return Line Feed, which are characters used to indicate the end of a line of text in HTTP headers. When CRLF characters are injected into user input fields or HTTP headers, attackers can manipulate the content of web pages or redirect users to malicious sites.

Why does CRLF Injection Occur?

CRLF injection vulnerabilities occur when web application developers fail to properly validate user input. This can happen for a variety of reasons, such as inadequate knowledge of secure coding practices, lack of resources, or time constraints. Attackers are constantly looking for vulnerabilities in web applications, and this is one that can be easily exploited.

You can perform various types of  Attacks:

XSS or Cross-Site Scripting: You can perform XSS with the help of CRLF injection by disabling the X-XSS protection header.

The following GET requests are crafted in an attempt to chain it with XSS:
By Popping an alert containing sensitive user information

Cookie Injection: With the help of CRLF injection you can set   your malicious cookie on the victim’s browser

Phishing Attacks:  An attacker can set the location header to redirect the victim to the malicious website. An attacker can perform open redirection with the help of it.

Session Fixation: This attack is similar to cookie injection. An attacker can set the user’s session id to a particular value.

HTTP Header Injection: An attacker can take advantage of it to defeat the security mechanisms by injecting the HTTP Header injection such as XSS filters or SOP(Same-Origin-Policy )etc.

Impact of CRLF Injection

The impact of CRLF injection can be severe. Attackers can use this vulnerability to inject phishing links, redirect users to malicious sites, steal sensitive user data, or even take control of the web application. This can result in financial losses, reputational damage, and legal liabilities for the affected organization. Additionally, users may lose trust in the web application and may be hesitant to use it again.

How to Prevent?

Preventing CRLF injection requires proper input validation and sanitation techniques. Here are some best practices to prevent this attacks:

Proper input validation: Web application developers should ensure that all user input fields and HTTP headers are properly sanitized and validated. This can be done by using regular expressions or other validation techniques to filter out CRLF characters.

Use secure coding practices: Web application developers should use secure coding practices, such as avoiding the use of user input directly in HTTP headers, using secure coding frameworks, and implementing secure communication protocols like HTTPS.

Security libraries and frameworks: Web application developers can use security libraries and frameworks that provide protection against this attacks.

Conduct regular security audits: Web application developers should conduct regular security audits to identify and fix vulnerabilities in their web applications.


Sahil Chaudhary

VAPT Analyst

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