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AA-2009.0149                  AUSCERT Advisory

                             [Win][UNIX/Linux]
                   Apache Web Server: Denial of Service
                               24 June 2009
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        AusCERT Advisory Summary
        ------------------------

Product:              Apache Web Server
Operating System:     UNIX variants (UNIX, Linux, OSX)
                      Windows
Impact:               Denial of Service
Access:               Remote/Unauthenticated
Member content until: Wednesday, July 22 2009

OVERVIEW:

       A tool has been released allowing attackers to perform denial of 
       service attacks against Apache Web servers.


IMPACT:

       The tool, named Slowloris, manages to maintain an open connection 
       by sending incomplete HTTP requests to the server, thereby exhausting
       avaialable Apache resources. Apache v1.x, 2.x and Squid are affected.
       This tool is currently active and available for download. [1, 2]


MITIGATION:

       For standalone Apache servers, some details regarding configuring
       the timeout between POST requests may provide an effective mitigation 
       strategy. [2]

       As yet the vendor has not released any details, however an unofficial
       patch is available. [3]


REFERENCES:

       [1] Apache HTTP DoS tool released
           http://isc.sans.org/diary.php?storyid=6601&rss

       [2] Apache HTTP DoS tool mitigation
           http://isc.sans.org/diary.php?storyid=6601&rss

       [3] Slowloris and Iranian DDoS attacks
           http://isc.sans.org/diary.php?storyid=6622&rss

AusCERT has made every effort to ensure that the information contained
in this document is accurate.  However, the decision to use the information
described is the responsibility of each user or organisation. The decision to
follow or act on information or advice contained in this security bulletin is
the responsibility of each user or organisation, and should be considered in
accordance with your organisation's site policies and procedures. AusCERT
takes no responsibility for consequences which may arise from following or
acting on information or advice contained in this security bulletin.

If you believe that your computer system has been compromised or attacked in 
any way, we encourage you to let us know by completing the secure National IT 
Incident Reporting Form at:

        http://www.auscert.org.au/render.html?it=3192

===========================================================================
Australian Computer Emergency Response Team
The University of Queensland
Brisbane
Qld 4072

Internet Email: auscert@auscert.org.au
Facsimile:      (07) 3365 7031
Telephone:      (07) 3365 4417 (International: +61 7 3365 4417)
                AusCERT personnel answer during Queensland business hours
                which are GMT+10:00 (AEST).
                On call after hours for member emergencies only.
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