CRLF stands for “Carriage Return” (\r) and “Line Feed” (\n), which signify the end of a line in many operating systems. CRLF injection attacks occur when these sequences are injected into an application, potentially leading to vulnerabilities.
🔥 Vulnerabilities Paired with CRLF:
CRLF can be paired with other vulnerabilities, like HTTP Response Splitting and XSS. By controlling response headers, attackers can manipulate the response body.
📝 CRLF Injection Example:
Request to the server:
GET /search?q=test%0D%0AInjected-Header:malicious_value HTTP/1.1 Host: vulnerable.website
Server response:
HTTP/1.1 200 OK Content-Type: text/html Injected-Header: malicious_value <body> ...website content... </body>
🔥 CRLF paired with XSS:
Request to the server:
GET /search?q=test%0D%0AContent-Length:%200%0D%0A%0D%0AHTTP/1.1%20200%20OK%0D%0AContent-Type:%20text/html%0D%0A%0D%0A%3Cscript%3Ealert('xss')%3C/script%3E HTTP/1.1 Host: vulnerable.website
Server response:
HTTP/1.1 200 OK Content-Type: text/html Content-Length: 0 HTTP/1.1 200 OK Content-Type: text/html <script>alert('xss')</script> <body> ...website content... </body>
🛠️ Remediation:
- Input Validation: Always validate and sanitize user inputs. Use allow-lists for expected inputs and reject any unexpected or malicious input.
- Utilize Safe Libraries: Many modern frameworks and libraries have built-in protection against CRLF injections. Utilize them and ensure they are regularly updated.
- Encode Data: Before reflecting user data in HTTP responses, ensure it’s properly encoded to prevent CRLF sequences.
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Set HTTPOnly and Secure Flags: For cookies, set the
HTTPOnlyandSecureflags to protect them from potential misuse if CRLF or other vulnerabilities are exploited. - Regularly Audit and Patch: Regularly scan and patch your applications for vulnerabilities. Utilize web application firewalls (WAF) for an added layer of security.
CRLF, while basic, can lead to more advanced attacks. Developers should be vigilant, employing best practices to counteract such vulnerabilities.
🔐 Stay Aware, Code Securely!
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