Unix and Linux → Apache 1.x/2.x Range header security issue

Title:    Range header DoS vulnerability Apache HTTPD 1.3/2.x
 
CVE:      CVE-2011-3192:
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 a full fix is available:
 
1) Use SetEnvIf or mod_rewrite to detect a large number of ranges
and then either ignore the Range: header or reject the request.
 
   Option 1: (Apache 2.0 and 2.2)
 
          # Drop the 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: (Also for Apache 1.3)
 
          # Reject request when more than 5 ranges in the Range: header.
          # CVE-2011-3192
          #
 
          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+K1Dqc7g@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.