[Case 52484] Range header DoS vulnerability Apache

Discussion in 'Masalah Teknik dan Keamanan' started by vishualhost, 4 Sep 2011.

Thread Status:
Not open for further replies.
  1. vishualhost

    vishualhost Expert 2.0

    Likes Received:
    Trophy Points:
    lagi browsing2 forum cpanel nemu thread ini

    Hash: SHA1

    Apache HTTPD Security ADVISORY
    UPDATE 2

    Title: Range header DoS vulnerability Apache HTTPD 1.3/2.x

    CVE: CVE-2011-3192
    Last Change: 20110826 1030Z
    Date: 20110824 1600Z
    Product: Apache HTTPD Web Server
    Versions: Apache 1.3 all versions, Apache 2 all versions

    Changes since last update
    In addition to the 'Range' header - the 'Range-Request' header is equally
    affected. Furthermore various vendor updates, improved regexes (speed and
    accommodating a different and new attack pattern).


    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 tool 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 24 hours.

    Background and the 2007 report

    There are two aspects to this vulnerability. One is new, is Apache specific;
    and resolved with this server side fix. The other issue is fundamentally a
    protocol design issue dating back to 2007:

    Bugtraq: a cheesy Apache / IIS DoS vuln (+a question)

    The contemporary interpretation of the HTTP protocol (currently) requires a
    server to return multiple (overlapping) ranges; in the order requested. This
    means that one can request a very large range (e.g. from byte 0- to the end)
    100's of times in a single request.

    Being able to do so is an issue for (probably all) webservers and currently
    subject of an IETF discussion to change the protocol:

    #311 (Add limitations to Range to reduce its use as a denial-of-service tool)

    This advisory details a problem with how Apache httpd and its so called
    internal 'bucket brigades' deal with serving such "valid" request. The
    problem is that currently such requests internally explode into 100's of
    large fetches, all of which are kept in memory in an inefficient way. This
    is being addressed in two ways. By making things more efficient. And by
    weeding out or simplifying requests deemed too unwieldy.


    There are several immediate options to mitigate this issue until a full fix
    is available. Below examples handle both the 'Range' and the legacy
    'Request-Range' with various levels of care.

    Note that 'Request-Range' is a legacy name dating back to Netscape Navigator
    2-3 and MSIE 3. Depending on your user community - it is likely that you
    can use option '3' safely for this older 'Request-Range'.

    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 2.2)

    # Drop the Range header when more than 5 ranges.
    # CVE-2011-3192
    SetEnvIf Range (?:,.*?){5,5} bad-range=1
    RequestHeader unset Range env=bad-range

    # We always drop Request-Range; as this is a legacy
    # dating back to MSIE3 and Netscape 2 and 3.
    RequestHeader unset Request-Range

    # optional logging.
    CustomLog logs/range-CVE-2011-3192.log common env=bad-range
    CustomLog logs/range-CVE-2011-3192.log common env=bad-req-range

    Above may not work for all configurations. In particular situations
    mod_cache and (language) modules may act before the 'unset'
    is executed upon during the 'fixup' phase.

    Option 2: (Pre 2.2 and 1.3)

    # Reject request when more than 5 ranges in the Range: header.
    # CVE-2011-3192
    RewriteEngine on
    RewriteCond %{HTTP:range} !(bytes=[^,]+(,[^,]+){0,4}$|^$)
    # RewriteCond %{HTTP:request-range} !(bytes=[^,]+(?:,[^,]+){0,4}$|^$)
    RewriteRule .* - [F]

    # We always drop Request-Range; as this is a legacy
    # dating back to MSIE3 and Netscape 2 and 3.
    RequestHeader unset Request-Range

    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: core - Apache HTTP Server

    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.

    Furthermore to ignore the Netscape Navigator 2-3 and MSIE 3 specific
    legacy header - add:

    RequestHeader unset Request-Range

    Unlike the commonly used 'Range' header - dropping the 'Request-Range'
    is not likely to affect many clients.

    4) Deploy a Range header count module as a temporary stopgap measure:


    Precompiled binaries for some platforms are available at:


    5) Apply any of the current patches under discussion - such as:

    Re: DoS with mod_deflate & range requests
    [Apache-SVN] Revision 1161534

    OS and Vendor specific information

    Red Hat: Option 1 cannot be used on Red Hat Enterprise Linux 4.

    NetWare: Pre compiled binaries available.

    mod_security: Has updated their rule set; see
    Mitigation of Apache Range Header DoS Attack - SpiderLabs Anterior


    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 - note 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.


    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 24 hours. Note that, while popular, Apache 1.3 is deprecated.

    - -- end of advisory - update 2
    Version: GnuPG v1.4.11 (Darwin)

    -----END PGP SIGNATURE-----

    untuk bugfixed apache sudah direlease tanggal 2 sept kemarin , jadi yg belum patching bisa segera force update via easyapache cpanel .
  2. prandah

    prandah Poster 2.0

    Likes Received:
    Trophy Points:
    kalo boleh tau itu apaan yak ?
Thread Status:
Not open for further replies.

Share This Page