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Date: Fri, 23 Aug 2013 08:48:12 +0000
From: Bart van Tuil <>
To: "" <>
Cc: "" <>
Subject: Re: [DAHAX-2013-001] Cloudflare XSS Vulnerability


Is it just me, or does it seem that **any** way to change the browser 
headers requires a degree of control that is same as, or higher than, 
the one we're trying to get?

I am sure there are a lot of ways (flash, javascript, objects) to 
modify headers. I just don't think it gets anyone anywhere.

Prereq > escalation? If someone finds an exception, I -am- listening ;)

Doesn't take away the fact that it's a nice find. Good going - thinking 
out of the box like this, Glenn.



From: Full-Disclosure [] On Behalf Of Julius Kivimäki
Sent: donderdag 22 augustus 2013 20:50
Subject: Re: [Full-disclosure] [DAHAX-2013-001] Cloudflare XSS Vulnerability

Heard of flash m8?

2013/8/22 <>
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


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

**Notification Timeline:**

* 10/07/2013, Request# 38713 (
* 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 (

## What?

* Reflected XSS (cross site scripting) attack

## Where's Affected?

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

## How?

* **To bring up the vulnerable page**
  - Set your X-Forwarded-For header to <del>72+</del> 101+ characters
  - 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]')</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]( (

## 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](

Full-Disclosure - We believe in it.
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Full-Disclosure - We believe in it.
Hosted and sponsored by Secunia -

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