The HTTP header injection vulnerability is a web application security term that refers to a situation when the attacker tricks the web application into inserting extra HTTP headers into legitimate HTTP responses. HTTP header injection is a specific case of a more generic category of attacks: CRLF injections.

What is 0A 0D?

Netscape ANSI encoded files use 0D 0D 0A for their line breaks. Apple mail has also been known to make an encoding error on text and csv attachments outbound. In essence it replaces line terminators with soft line breaks on each line, which look like =0D in the encoding.

How does CRLF injection work?

CRLF Injection Defined Exploits occur when an attacker is able to inject a CRLF sequence into an HTTP stream. By introducing this unexpected CRLF injection, the attacker is able to maliciously exploit CRLF vulnerabilities in order to manipulate the web application’s functions.

What is CRLF injection attack?

CRLF injections are vulnerabilities where the attacker is able to inject CR (carriage return, ASCII 13) and LF (line feed, ASCII 10) characters into the web application. This lets the attacker add extra headers to HTTP responses or even make the browser ignore the original content and process injected content instead.

What is HTTP parser attack?

HTTP parser attacks attempt to execute malicious code, extract information, or enact Denial of Service by targeting the HTTP parser directly. HTTP Request Smuggling. HTTP Request Smuggling attacks attempt to encapsulate one request within another request through a web proxy.

What are CR and LF characters?

CR = Carriage Return ( \r , 0x0D in hexadecimal, 13 in decimal) — moves the cursor to the beginning of the line without advancing to the next line. LF = Line Feed ( \n , 0x0A in hexadecimal, 10 in decimal) — moves the cursor down to the next line without returning to the beginning of the line.

What is end of line sequence?

The End of Line (EOL) sequence ( 0x0D 0x0A , \r\n ) is actually two ASCII characters, a combination of the CR and LF characters. It moves the cursor both down to the next line and to the beginning of that line.

What is HTTP parser?

The HTTP Parser interprets a byte stream according to the HTTP specification. This Parser is used by the HTTP Client Connector and by the HTTP Server Connector.

How does HTTP parser attack work?

HTTP parser attacks attempt to execute malicious code, extract information, or enact Denial of Service by targeting the HTTP parser directly. Remote file location attacks attempt to exploit web applications that may retrieve and execute the code included in remote files.

What is HTML injection example?

Another common application of HTML injection is to create a form on the target page and get the data entered in that form. For example, the attacker may inject malicious code with a fake login form. The form data (login and password) would then be sent to a server controlled by the attacker.

What is the big risk of HTML injection?

An injection allows the attacker to send a malicious HTML page to a victim. The targeted browser will not be able to distinguish (trust) legitimate parts from malicious parts of the page, and consequently will parse and execute the whole page in the victim’s context.

What is Header injection and how does it work?

Header injection in HTTP responses can allow for HTTP response splitting, Session fixation via the Set-Cookie header, cross-site scripting (XSS), and malicious redirect attacks via the location header. HTTP header injection is a relatively new area for web-based attacks, and has primarily been pioneered by Amit Klein in his…

Can an attacker inject newline characters into an HTTP response header?

If an attacker can inject newline characters into the header, then they can inject new HTTP headers and also, by injecting an empty line, break out of the headers into the message body and write arbitrary content into the application’s response. Various kinds of attack can be delivered via HTTP response header injection vulnerabilities.

What are the HTTP response header injection vulnerabilities?

HTTP response header injection vulnerabilities arise when user-supplied data is copied into a response header in an unsafe way.

How to mitigate against email header injection?

Mitigating against email header injection involves validating user input. You must not allow any newline characters in the input because they let the attacker append email headers. In general, when validating user input, the simplest and most robust way to achieve strong input validation is through a whitelist of allowed characters.