nginx and Apache killer

[Jim Ohlstein]

On 8/27/11 4:11 AM, Igor Sysoev wrote:
> Following "Apache Killer" discussions and the advisory from 2011-08-24
> (Advisory: Range header DoS vulnerability Apache HTTPD 2.x CVE-2011-3192)
> we'd like to clarify a couple of things in regards to nginx behavior
> either in standalone or "combo" (nginx+apache) modes.
> 
> First of all, nginx doesn't favor HEAD requests with compression,
> so the exact mentioned attack doesn't work against a standalone
> nginx installation.
> 
> If you're using nginx in combination with proxying to apache backend,
> please check your configuration to see if nginx actually passes range
> requests to the backend:
> 
> 1) If you're using proxying WITH caching then range requests are not
> sent to backend and your apache should be safe.
> 
> 2) If you're NOT using caching then you might be vulnerable to the attack.
> 
> In order to mitigate this attack when your installation includes
> apache behind nginx we recommend you the following:
> 
> 1. Refer to the above mentioned security advisory CVE-2011-3192 for apache
> and implement described measures accordingly.

Apache 2.2.20 has been released to address this issue. Please see
http://www.apache.org/dist/httpd/Announcement2.2.html.


> 
> 2. Consider using nginx configuration below (in server{} section of
> configuration). This particular example filters 5 and more ranges
> in the request:
> 
>   if ($http_range ~ "(?:\d*\s*-\s*\d*\s*,\s*){5,}") {
>       return 416;
>   }
> 
> We'd also like to notify you that for standalone nginx installations
> we've produced the attached patch. This patch prevents handling
> malicious range requests at all, instead outputting just the entire file
> if the total size of all ranges is greater than the expected response.
> 
> 
> 
> 
> 
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-- 
Jim Ohlstein