Some hints and tips on security issues in setting up a web server. Some of the suggestions will be general, others specific to Apache.
In typical operation, Apache is started by the root
user, and it switches to the user defined by the
/usr/local/apache then it is
suggested that you create that directory as root, with commands
It is assumed that /, /usr, and /usr/local are only modifiable by root. When you install the httpd executable, you should ensure that it is similarly protected:mkdir /usr/local/apache cd /usr/local/apache mkdir bin conf logs chown 0 . bin conf logs chgrp 0 . bin conf logs chmod 755 . bin conf logs
cp httpd /usr/local/apache/bin chown 0 /usr/local/apache/bin/httpd chgrp 0 /usr/local/apache/bin/httpd chmod 511 /usr/local/apache/bin/httpd
You can create an htdocs subdirectory which is modifiable by other users -- since root never executes any files out of there, and shouldn't be creating files in there.
If you allow non-root users to modify any files that root either executes or writes on then you open your system to root compromises. For example, someone could replace the httpd binary so that the next time you start it, it will execute some arbitrary code. If the logs directory is writeable (by a non-root user), someone could replace a log file with a symlink to some other system file, and then root might overwrite that file with arbitrary data. If the log files themselves are writeable (by a non-root user), then someone may be able to overwrite the log itself with bogus data.
Server side includes (SSI) can be configured so that users can execute arbitrary programs on the server. That thought alone should send a shiver down the spine of any sys-admin.
One solution is to disable that part of SSI. To do that you use the
IncludesNOEXEC option to the
Allowing users to execute CGI scripts in any directory should only be considered if;
Limiting CGI to special directories gives the admin control over what goes into those directories. This is inevitably more secure than non script aliased CGI, but only if users with write access to the directories are trusted or the admin is willing to test each new CGI script/program for potential security holes.
Most sites choose this option over the non script aliased CGI approach.
Always remember that you must trust the writers of the CGI script/programs or your ability to spot potential security holes in CGI, whether they were deliberate or accidental.
All the CGI scripts will run as the same user, so they have potential to
conflict (accidentally or deliberately) with other scripts e.g.
User A hates User B, so he writes a script to trash User B's CGI
database. One program which can be used to allow scripts to run
as different users is
To run a really tight ship, you'll want to stop users from setting
.htaccess files which can override security features
you've configured. Here's one way to do it...
In the server configuration file, put
Then setup for specific directories
allow from all
This stops all overrides, Includes and accesses in all directories apart from those named.
One aspect of Apache which is occasionally misunderstood is the feature of default access. That is, unless you take steps to change it, if the server can find its way to a file through normal URL mapping rules, it can serve it to clients.
For instance, consider the following example:
This would allow clients to walk through the entire filesystem. To work around this, add the following block to your server's configuration:
<Directory /> Order deny,allow Deny from all </Directory>
This will forbid default access to filesystem locations. Add
<Directory /usr/users/*/public_html> Order deny,allow Allow from all </Directory> <Directory /usr/local/httpd> Order deny,allow Allow from all </Directory>
Pay particular attention to the interactions of
Also be wary of playing games with the
Please send any other useful security tips to The Apache Group
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