see inline updates
On Wed, Aug 24, 2011 at 10:56 AM, Dirk-Willem van Gulik
<[email protected]> wrote:
> Various suggest on-list and off-list fixes applied. Thanks all.
>
> A few more +1's would be nice :)
>
> Dw.
>
>
>
>
>
> Title: CVE-2011-3192: Range header DoS vulnerability Apache HTTPD 1.3/2.x
> Apache HTTPD Security ADVISORY
>
> Date: 20110824 1600Z
> Product: Apache HTTPD Web Server
> Versions: Apache 1.3 all versions, Apache 2 all versions
>
> Description:
> ------------
>
> A denial of service vulnerability has been found in the way the multiple
> overlapping ranges are handled by the Apache HTTPD server:
>
> http://seclists.org/fulldisclosure/2011/Aug/175
>
> An attack tool is circulating in the wild. Active use of this tools has been
> observed.
>
> The attack can be done remotely and with a modest number of requests can
> cause very significant memory and CPU usage on the server.
>
> The default Apache HTTPD installation is vulnerable.
>
> There is currently no patch/new version of Apache HTTPD which fixes this
> vulnerability. This advisory will be updated when a long term fix is
> available.
>
> A full fix is expected in the next 48 hours.
>
> Mitigation:
> ------------
>
> However there are several immediate options to mitigate this issue until that
> time.
>
> 1) Use mod_rewrite to limit the number of ranges:
^ clarify due to directive addition
>
> Option 1:
> # drop Range header when more than 5 ranges.
> # CVE-2011-3192
> SetEnvIf Range (,.*?){5,} bad-range=1
> RequestHeader unset Range env=bad-range
>
> # optional logging.
> CustomLog logs/range-CVE-2011-3192.log common env=bad-range
>
> Option 2:
> # Reject request when more than 5 ranges in the Range: header.
> # CVE-2011-3192. Must be added to each VirtualHost and once
> # in the base configuration.
+RewriteEngine on
> RewriteCond %{HTTP:range} !(^bytes=[^,]+(,[^,]+){0,4}$|^$)
> RewriteRule .* - [F]
>
> The number 5 is arbitrary. Several 10's should not be an issue and may be
> required for sites which for example serve PDFs to very high end eReaders
> or use things such complex http based video streaming.
>
> 2) Limit the size of the request field to a few hundred bytes. Note that
> while this
> keeps the offending Range header short - it may break other headers; such as
> sizeable cookies or security fields.
>
> LimitRequestFieldSize 200
>
> Note that as the attack evolves in the field you are likely to have
> to further limit this and/or impose other LimitRequestFields limits.
>
> See: http://httpd.apache.org/docs/2.2/mod/core.html#limitrequestfieldsize
>
> 3) Use mod_headers to completely dis-allow the use of Range headers:
>
> RequestHeader unset Range
>
> Note that this may break certain clients - such as those used for
> e-Readers and progressive/http-streaming video.
>
> 4) Deploy a Range header count module as a temporary stopgap measure:
>
> http://people.apache.org/~dirkx/mod_rangecnt.c
>
> Precompiled binaries for some platforms are available at:
>
> http://people.apache.org/~dirkx/BINARIES.txt
>
> 5) Apply any of the current patches under discussion - such as:
>
>
> http://mail-archives.apache.org/mod_mbox/httpd-dev/201108.mbox/%3ccaapsnn2po-d-c4nqt_tes2rrwizr7urefhtkpwbc1b+k1dq...@mail.gmail.com%3e
>
> Actions:
> -----------
> Apache HTTPD users who are concerned about a DoS attack against their server
> should consider implementing any of the above mitigations immediately.
>
> When using a third party attack tool to verify vulnerability - know that most
> of the versions in the wild currently check for the presence of mod_deflate;
> and will (mis)report that your server is not vulnerable if this module is not
> present. This vulnerability is not dependent on presence or absence of that
> module.
>
> Planning:
> -------------
> This advisory will be updated when new information, a patch or a new release
> is available. A patch or new apache release for Apache 2.0 and 2.2 is
> expected in the next 48 hours. Note that, while popular, Apache 1.3 is
> deprecated.
>
>
--
Eric Covener
[email protected]
