A CRLF injection attachồng is one of several types of injection attacks. It can be used to escalate lớn more malicious attacks such as Cross-site Scripting (XSS), page injection, web cađậy poisoning, cache-based defacement, and more. A CRLF injection vulnerability exists if an attacker can inject the CRLF characters into a website application, for example using a user input đầu vào size or an HTTP. request.quý khách hàng sẽ xem: Crlf là gì

The CRLF abbreviation refers lớn Carriage Return and Line Feed. CR và LF are special characters (ASCII 13 and 10 respectively, also referred lớn as ) that are used khổng lồ signify the End of Line (EOL). The CRLF sequence is used in operating systems including Windows (but not Linux/UNIX) & Internet protocols including HTTP.

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There are two most comtháng uses of CRLF injection attacks: log poisoning & HTTP response splitting. In the first case, the attacker falsifies log tệp tin entries by inserting an kết thúc of a line & an extra line. This can be used to hide other attacks or to confuse system administrators. In the second case, CRLF injection is used to lớn add HTTP. headers to lớn the HTTPhường. response &, for example, perform an XSS attachồng that leads to information disclosure. A similar technique, called Email Header Injection, may be used khổng lồ add SMTP headers to emails.


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What Is HTTP. Response Splitting

The HTTPhường. protocol uses the CRLF character sequence to lớn signify where one header ends và another begins. It also uses it to lớn signify where headers over & the website nội dung begins.

If the attacker inserts a single CRLF, they can add a new header. If it is, for example, a Location header, the attacker can redirect the user to a different website. Criminals may use this technique for phishing or defacing. This technique is often called HTTPhường header injection.

If the attacker inserts a double CRLF, they can prematurely terminate HTTP headers & inject content before the actual trang web content. The injected content can contain JavaScript code. It can also be formulated so that the actual website content coming from the website VPS is ignored by the web browser. This is how HTTPhường. response splitting is used in combination with Cross-site Scripting (XSS).

The following simplified example uses CRLF to:

Add a fake HTTP response header: Content-Length: 0. This causes the web browser to lớn treat this as a terminated response & begin parsing a new response.Add a kém chất lượng HTTPhường. response: HTTP/1.1 200 OK. This begins the new response.Add another fake HTTP response header: Content-Type: text/html. This is needed for the website browser khổng lồ properly parse the content.Add yet another kém chất lượng HTTP response header: Content-Length: 25. This causes the web browser lớn only parse the next 25 bytes.Add page content with an XSS: . This nội dung has exactly 25 bytes.Because of the Content-Length header, the website browser ignores the original content that comes from the website VPS.

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Finding and Mitigating CRLF Injections

The impact of CRLF injections may seem lớn be limited. CRLF injections are not even mentioned in the OWASPhường. top 10 2017 website application security list. However, attackers can effectively use CRLF injections to escalate to lớn much more serious attacks that exploit other website application vulnerabilities. Therefore, you should treat CRLF injection vulnerabilities seriously.

Fortunately, it’s easy to lớn thử nghiệm if your website or website application is vulnerable to lớn CRLF injections and other vulnerabilities by running an automated web scan using the hjwitteveen.com vulnerability scanner. Take a thử nghiệm and find out more about running a scan against your website or website application.

CRLF injection vulnerabilities are usually mitigated by website frameworks automatically. Even if the vulnerability is not mitigated, it is very simple to lớn fix:

Option 1: Rework your code so that content supplied by the user is never used directly in the HTTPhường stream.Option 2: Strip any newline characters before passing nội dung inlớn the HTTPhường header.Option 3: Encode the data that you pass into HTTPhường. headers. This will effectively scramble the CR và LF codes if the attacker attempts to lớn inject them.

How khổng lồ Prsự kiện CRLF Injections

CRLF injection vulnerabilities are usually mitigated by web frameworks automatically. Even if the vulnerability is not mitigated, it is very simple to lớn fix.


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Step 1: Don’t trust user input

Rework your code so that content supplied by the user is never used directly in the HTTPhường stream.

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Step 4: Scan regularly (with hjwitteveen.com)

CRLF injections may be introduced by your developers or through external libraries/modules/software. You should regularly scan your web applications using a web vulnerability scanner such as hjwitteveen.com. If you use Jenkins, you should install the hjwitteveen.com plugin lớn automatically scan every build.
Chuyên mục: Hỏi Đáp
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