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From Bill Moseley <mose...@best.com>
Subject general/5412: potential denial-of-service with CLOSE_WAIT
Date Fri, 03 Dec 1999 14:22:33 GMT

>Number:         5412
>Category:       general
>Synopsis:       potential denial-of-service with CLOSE_WAIT
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    apache
>State:          open
>Class:          sw-bug
>Submitter-Id:   apache
>Arrival-Date:   Fri Dec  3 06:30:01 PST 1999
>Originator:     moseley@best.com
>Release:        1.3.9
SunOS sunsite 5.6 Generic_105181-16 sun4u sparc SUNW,Ultra-Enterprise
server-status showed six of 30 children sitting in 'D' status for a long time.  
All were requesting the same URL. All were different IP numbers, 
but all from the same network.

Hostnamelookups are off, but there was an .htaccess with a deny from a 
host name.  I assume that 'D' wasn't actually correct, that rather 'D'
had finished and was waiting on the connection to move to 'W'.
Correct assumption?

netstat showed all the connections in CLOSE_WAIT status.  A traceroute to
each of the IPs failed to connect to the remote host.  (Perhaps dynamic IPs)

Placing a connection in CLOSE_WAIT is a commonly know denial-of-service attack.
I'm not sure if this was our case or not.  

The Apache children were blocked from servicing requests for about 2 hours.
That 2 hours may have been the CLOSE_WAIT TCP timeout.

I can imagine a situation where someone manages to tie up MaxClients all in 
CLOSW_WAIT state and shut down httpd service.

I don't know network programming, but would it be possible for Apache to timeout
those connections and continue working without waiting for the socket?
We have our timeout setting at 180, and that works properly.

Thansks for your time.


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