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Apache 2.0.49 places no limit on the amount of folding of input headers, or in the total length after folding. With an input stream with infinite headers to be folded, the server will allocate as much memory as the system will allow, possibly leading to a denial of service. Public by Georgi Guninski to full-disclosure on Jun28 CAN-2004-0493 Affects: 3AS 3WS 3ES 3Desktop
The original report by Guninski is to be found at http://www.guninski.com/httpd1.html
Quick thought for a workaround while this gets straigtened out: Use ulimit -d to limit the amount of data memory that any one httpd process can have. Make it high enough to function for whatever purpose you use httpd for, but lower than all of memory (i.e. unlimited) I can recall if allocations above 'ulimit -d' core out the process or return ENOMEM, but if they do the former, enable core files, and write a cron job to clean up and restart any crashed httpd processes. This should prevent significant system slow down, and allow for a modest prevention of the DoS attack.
An errata has been issued which should help the problem described in this bug report. This report is therefore being closed with a resolution of ERRATA. For more information on the solution and/or where to find the updated files, please follow the link below. You may reopen this bug report if the solution does not work for you. http://rhn.redhat.com/errata/RHSA-2004-342.html