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Re: [DAHAX-2013-001] Cloudflare XSS Vulnerability
From: Julius Kivimäki <julius.kivimaki () gmail com>
Date: Thu, 22 Aug 2013 21:50:27 +0300

Heard of flash m8?


2013/8/22 <xnite () xnite org>

**

That's a nice trick and all, but I don't see how it's valuable. In order
to trigger the XSS you need to modify your browser headers, therefore any
victim who you are trying to get to a page to execute your XSS would need
to also modify THEIR browser headers. I don't see how this is any thing
more than a neat trick. Sorry.


On Thursday 22 August 2013 23:18:03 Glenn Grant wrote:

Details below of an XSS vulnerability I discovered in Cloudflare (markdown
format)


- Glenn | /dev/alias

* http://blog.devalias.net

* http://devalias.net


-----


**Reference Number:** DAHAX-2013-001 (/dev/alias/hacks 2013-001)


**Notification Timeline:**


* 10/07/2013, Request# 38713 (
https://support.cloudflare.com/anonymous_requests/new)

* 10/07/2013, Vendor looking into issue

* 16/07/2013, Updated vendor with new details (Length: 101 instead of 72)

* 16/07/2013, Vendor requested that I test again

* [No further response from vendor]

* 01/08/2013, Tested again, vulnerability fixed


**Details Published:** 14/08/2013 (
http://blog.devalias.net/post/58217238426/dahax-2013-001-cloudflare-xss-vulnerability
)


## What?


* Reflected XSS (cross site scripting) attack


## Where's Affected?


* Theoretically it seems that any page that uses cloudflare will be
affected.

  - Eg: http://www.cloudflare.com/


## How?


* **To bring up the vulnerable page**

  - Set your X-Forwarded-For header to <del>72+</del> 101+ characters

    - <del>Eg: X-Forwarded-For:
AAAAAAAAAABBBBBBBBBBCCCCCCCCCCDDDDDDDDDDEEEEEEEEEEFFFFFFFFFFGGGGGGGGGGHH</del>

    - Eg: <pre>X-Forwarded-For:
AAAAAAAAAABBBBBBBBBBCCCCCCCCCCDDDDDDDDDDEEEEEEEEEEFFFFFFFFFFGGGGGGGGGGHHHHHHHHHHIIIIIIIIIIJJJJJJJJJJK</pre>

  - Load a site using cloudflare

  - You should end up on "DNS Points to Prohibited IP" page


* **To trigger the XSS**

  - Set your User-Agent string to the XSS attack

    - Eg: <pre>User-Agent: USER-AGENT being tested for
XSS..<script>alert('Vulnerable to XSS via USER-AGENT header [Found by
devalias.net]')</script></pre>


* **The whole attack**

  - Ensure your X-Forwarded-For and User-Agent headers are configured as
above

  - Navigate to a page using cloudflare

  - ???

  - Profit!


## Who?


* Discovered by [Glenn '/dev/alias' Grant](http://www.devalias.net/) (
glenn () devalias net)


## Responsible Disclosure Notice


* Following in the footsteps of Google's vulnerability disclosure
timeline, unless otherwise agreed to beforehand, I reserve the right to
publicly announce the details of any discovered vulnerabilities 7 days post
notification.

  * **Google's Rationale:** "Seven days is an aggressive timeline and may
be too short for some vendors to update their products, but it should be
enough time to publish advice about possible mitigations, such as
temporarily disabling a service, restricting access, or contacting the
vendor for more information. As a result, after 7 days have elapsed without
a patch or advisory, we will support researchers making details available
so that users can take steps to protect themselves. By holding ourselves to
the same standard, we hope to improve both the state of web security and
the coordination of vulnerability management." - [Google](
http://googleonlinesecurity.blogspot.com.au/2013/05/disclosure-timeline-for-vulnerabilities.html
)




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_______________________________________________
Full-Disclosure - We believe in it.
Charter: http://lists.grok.org.uk/full-disclosure-charter.html
Hosted and sponsored by Secunia - http://secunia.com/

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