Results 1 to 6 of 6

Thread: Apache warns Web server admins of DoS attack tool

  1. #1
    Platinum Member SilverNodashi's Avatar
    Join Date
    May 2007
    Location
    Johannesburg, South Africa
    Posts
    1,197
    Thanks
    12
    Thanked 188 Times in 136 Posts

    Apache warns Web server admins of DoS attack tool

    Anyone who runs an Apache webserver should urgently look into securing their server(s) ASAP to avoid any DDOS attacks, as per this email from Apache:

    From: dirkx @ apache.org (Dirk-Willem van Gulik)
    > Subject: Advisory: Range header DoS vulnerability Apache HTTPD 1.3/2.x \(CVE-2011-3192\)
    > Date: August 24, 2011 9:16:39 AM PDT
    > To: announce@httpd.apache.org
    >
    >
    BEGIN PGP SIGNED MESSAGE

    > Hash: SHA1
    >
    > Apache HTTPD Security ADVISORY
    > ==============================
    >
    > 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:
    >
    > Full Disclosure: Apache Killer
    >
    > 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...questfieldsize
    >
    > 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_...l.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.
    Get superfast South African Hosting at WebHostingZone

  2. #2
    Platinum Member SilverNodashi's Avatar
    Join Date
    May 2007
    Location
    Johannesburg, South Africa
    Posts
    1,197
    Thanks
    12
    Thanked 188 Times in 136 Posts
    If you're using CentOS / Red Hat and probably any other Red Hat derivative like Fedora Core or Scientific Linux then you can apply the following fix:

    create a file in /etc/httpd/conf.d/ like for example "/etc/httpd/conf.d/CVE-2011-3192.conf" and add the following to the file:
    Code:
      # 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

    I'm not sure if this structure will work on Debian / Ubuntu / OpenSuse / etc systems, but on Red Hat type Linux systems Apache will read any file in the /etc/httpd/conf.d/ folder with a .conf extension.
    Get superfast South African Hosting at WebHostingZone

  3. Thanks given for this post:

    Dave A (26-Aug-11)

  4. #3
    Email problem
    Join Date
    Feb 2011
    Location
    Cape Town
    Posts
    323
    Thanks
    87
    Thanked 24 Times in 22 Posts
    Friends don't let friends use RedHat.

  5. #4
    Platinum Member SilverNodashi's Avatar
    Join Date
    May 2007
    Location
    Johannesburg, South Africa
    Posts
    1,197
    Thanks
    12
    Thanked 188 Times in 136 Posts
    Quote Originally Posted by Andrew_ZA View Post
    Friends don't let friends use RedHat.
    How hard did your hosting company laugh when you told them that??
    Get superfast South African Hosting at WebHostingZone

  6. #5
    Email problem
    Join Date
    Feb 2011
    Location
    Cape Town
    Posts
    323
    Thanks
    87
    Thanked 24 Times in 22 Posts
    Pointless wasting energy trying to convince them to use FreeBSD.

  7. #6
    Diamond Member AndyD's Avatar
    Join Date
    Jan 2010
    Location
    Cape Town
    Posts
    4,923
    Thanks
    576
    Thanked 934 Times in 755 Posts
    Quote Originally Posted by Andrew_ZA View Post
    Friends don't let friends use RedHat.
    _______________________________________________

    _______________________________________________

Similar Threads

  1. [Article] How to Use Email As a Viral Marketing Tool
    By derekjay in forum Marketing Forum
    Replies: 8
    Last Post: 28-Jul-10, 09:12 PM
  2. Free survey tool
    By duncan drennan in forum General Business Forum
    Replies: 2
    Last Post: 11-Oct-09, 11:18 PM
  3. ANC starts attack on Zille.
    By Dave A in forum South African Politics Forum
    Replies: 4
    Last Post: 01-Nov-06, 03:02 PM

Did you like this article? Share it with your favourite social network.

Did you like this article? Share it with your favourite social network.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •