
Carriage Return and Line Feed (CRLF) are special character elements typically embedded in Hypertext Transfer Protocol (HTTP) headers and some other software code. The inclusion of these character elements is to denote an End of Line (EOL) marker. These character elements are actually very common as many protocols of the Internet Protocol (IP) Suite, such as HTTP, MIME, and NNTP, use them to discretely split the text into elements. As such, CRLF injection is when an attacker can inject a sequence of CRLF into one of these protocols or software applications; such as an HTTP stream. This is one of the attacks most common uses and as such, has the alternative names of HTTP Response Splitting and Neutralization of CRLF Sequences in HTTP Headers.