[UNIX] Apache Mis-configuration Can Make You Vulnerable to a Local Denial of Service Attack

From: support@securiteam.com
Date: 01/15/02

From: support@securiteam.com
To: list@securiteam.com
Date: Tue, 15 Jan 2002 09:49:56 +0100 (CET)

The following security advisory is sent to the securiteam mailing list, and can be found at the SecuriTeam web site: http://www.securiteam.com
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  Apache Mis-configuration Can Make You Vulnerable to a Local Denial of
Service Attack


A common mis-configuration can occur within major ASP/Hosting sites,
whereas a remote hosting administrator is allowed access to its logging
directories with write access. This would open up the server to a local
denial of service, since Apache will not start if one of its logging
directories is missing, or cannot be accessed.


The problem occurs when the log directory does not exist, when Apache
receives, a SIGHUP (e.g. when logrotate runs) Apache will reload its
configuration file and shutdown immediately. Therefore, if the log
directory is removed by the owner of the domain by accident or because he
just wanted to clean up some logs, apache will just simply shutdown upon a

Vendor response:
The documentation explicitly states that you must not allow non-trusted
users write access to the logs directory. It is a major security hole
because they are opened by the user that starts Apache (normally user
root). This is a done on purpose, however it requires that the server to
be misconfigured. If you have a setup where a random user can write to
the logs directory, then you have a lot more to worry about than they
causing the server to not start.

Having a non-existent log directory is considered a major configuration
error, and it is not appropriate for Apache to blindly continue on trying
to guess what it should do (and possibly not logging anything).

Also, note that it is not only missing log directories that will cause
Apache to fail to startup correctly, but there are a number of major
configuration errors that will cause it to do the same thing.


The information has been provided by <mailto:tozz@embrace.selwerd.nl>
Tozz and <mailto:marcs@znep.com> Marc Slemko.


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