Apache: Keamanan
Sumber: http://httpd.apache.org/docs/2.0/misc/security_tips.html
Pastikan Software Up to Date
Apache HTTP Server memiliki catatan yang baik untuk keamanan dan komunitas pengembang yang sangat mengkhawatirkan masalah keamanan. Tetapi tidak dapat dihindari bahwa beberapa masalah - kecil atau besar - akan ditemukan dalam perangkat lunak setelah dilepaskan. Untuk alasan ini, sangat penting untuk menjaga menyadari update perangkat lunak. Jika Anda telah mendapatkan versi HTTP Server langsung dari Apache, kami sangat menyarankan Anda berlangganan ke Apache HTTP Server Pengumuman Daftar di mana Anda dapat menyimpan informasi dari rilis baru dan update keamanan. Layanan serupa yang tersedia dari yang paling distributor pihak ketiga perangkat lunak Apache.
Tentu saja, yang paling kali web server terganggu, itu bukan karena masalah dalam kode HTTP Server. Sebaliknya, itu berasal dari masalah dalam add-on kode, script CGI, atau Sistem Operasi yang mendasari. Oleh karena itu Anda harus tetap menyadari masalah dan update dengan semua perangkat lunak pada sistem Anda.
Permission pada ServerRoot Directory
Dalam operasi biasa, Apache dimulai oleh root, dan beralih ke pengguna didefinisikan oleh direktif pengguna untuk melayani hits. Seperti halnya dengan perintah yang mengeksekusi root, anda harus berhati-hati bahwa itu dilindungi dari modifikasi oleh pengguna non-root. Tidak hanya harus file sendiri bisa ditulisi hanya oleh root, tapi begitu harus direktori, dan parent dari semua direktori. Misalnya, jika Anda memilih untuk menempatkan ServerRoot di / usr / local / apache maka disarankan agar Anda membuat direktori sebagai root, dengan perintah seperti ini:
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
Hal ini diasumsikan bahwa /, / usr, dan / usr / local hanya dimodifikasi oleh root. Ketika Anda menginstal httpd executable, Anda harus memastikan bahwa itu sama dilindungi:
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
Anda dapat membuat subdirektori htdocs yang dapat dimodifikasi oleh pengguna lain - karena root tidak pernah mengeksekusi file diluar dari sana, dan tidak boleh menciptakan file di sana.
Jika Anda memungkinkan pengguna non-root untuk memodifikasi file yang dapat root eksekusi atau tulis maka anda membuka sistem anda untuk root compromise. Misalnya, seseorang bisa menggantikan biner httpd sehingga waktu berikutnya anda memulainya, itu akan mengeksekusi beberapa kode yang tidak kita ketahui. Jika direktori log dapat ditulis (oleh pengguna non-root), seseorang bisa mengganti file log dengan symlink untuk beberapa file sistem lainnya, dan kemudian root mungkin menimpa file dengan data yang tidak kita ketahui. Jika log file yang ditulisi (oleh pengguna non-root), maka seseorang mungkin dapat menimpa log itu dengan data palsu.
Server Side Includes
Server Side Includes (SSI) menyajikan administrator server dengan beberapa potensi risiko keamanan.
The first risk is the increased load on the server. All SSI-enabled files have to be parsed by Apache, whether or not there are any SSI directives included within the files. While this load increase is minor, in a shared server environment it can become significant.
SSI files also pose the same risks that are associated with CGI scripts in general. Using the exec cmd element, SSI-enabled files can execute any CGI script or program under the permissions of the user and group Apache runs as, as configured in httpd.conf.
There are ways to enhance the security of SSI files while still taking advantage of the benefits they provide.
To isolate the damage a wayward SSI file can cause, a server administrator can enable suexec as described in the CGI in General section.
Enabling SSI for files with .html or .htm extensions can be dangerous. This is especially true in a shared, or high traffic, server environment. SSI-enabled files should have a separate extension, such as the conventional .shtml. This helps keep server load at a minimum and allows for easier management of risk.
Another solution is to disable the ability to run scripts and programs from SSI pages. To do this replace Includes with IncludesNOEXEC in the Options directive. Note that users may still use <--#include virtual="..." --> to execute CGI scripts if these scripts are in directories designated by a ScriptAlias directive.
CGI in General
First of all, you always have to remember that you must trust the writers of the CGI scripts/programs or your ability to spot potential security holes in CGI, whether they were deliberate or accidental. CGI scripts can run essentially arbitrary commands on your system with the permissions of the web server user and can therefore be extremely dangerous if they are not carefully checked.
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 suEXEC which is included with Apache as of 1.2 and is called from special hooks in the Apache server code. Another popular way of doing this is with CGIWrap.
Non Script Aliased CGI
Allowing users to execute CGI scripts in any directory should only be considered if:
- You trust your users not to write scripts which will deliberately or accidentally expose your system to an attack.
- You consider security at your site to be so feeble in other areas, as to make one more potential hole irrelevant.
- You have no users, and nobody ever visits your server.
Script Aliased CGI
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.
Other sources of dynamic content
Embedded scripting options which run as part of the server itself, such as mod_php, mod_perl, mod_tcl, and mod_python, run under the identity of the server itself (see the User directive), and therefore scripts executed by these engines potentially can access anything the server user can. Some scripting engines may provide restrictions, but it is better to be safe and assume not.
Protecting System Settings
To run a really tight ship, you'll want to stop users from setting up .htaccess files which can override security features you've configured. Here's one way to do it.
In the server configuration file, put
<Directory /> AllowOverride None </Directory>
This prevents the use of .htaccess files in all directories apart from those specifically enabled.
Protect Server Files by Default
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:
# cd /; ln -s / public_html Accessing http://localhost/~root/
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 appropriate Directory blocks to allow access only in those areas you wish. For example,
<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 Location and Directory directives; for instance, even if <Directory /> denies access, a <Location /> directive might overturn it.
Also be wary of playing games with the UserDir directive; setting it to something like ./ would have the same effect, for root, as the first example above. If you are using Apache 1.3 or above, we strongly recommend that you include the following line in your server configuration files:
UserDir disabled root
Watching Your Logs
To keep up-to-date with what is actually going on against your server you have to check the Log Files. Even though the log files only reports what has already happened, they will give you some understanding of what attacks is thrown against the server and allow you to check if the necessary level of security is present.
A couple of examples:
grep -c "/jsp/source.jsp?/jsp/ /jsp/source.jsp??" access_log grep "client denied" error_log | tail -n 10
The first example will list the number of attacks trying to exploit the Apache Tomcat Source.JSP Malformed Request Information Disclosure Vulnerability, the second example will list the ten last denied clients, for example:
[Thu Jul 11 17:18:39 2002] [error] [client foo.bar.com] client denied by server configuration: /usr/local/apache/htdocs/.htpasswd
As you can see, the log files only report what already has happened, so if the client had been able to access the .htpasswd file you would have seen something similar to:
foo.bar.com - - [12/Jul/2002:01:59:13 +0200] "GET /.htpasswd HTTP/1.1"
in your Access Log. This means you probably commented out the following in your server configuration file:
<Files ~ "^\.ht"> Order allow,deny Deny from all </Files>