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Apache and PHP Security 



 

 
 
Tags:  webserver  security  web  tips 
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Published:  December 15, 2009
 
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Slide 1: Apache and PHP Security
Slide 2: Abbreviated Talk Outline… A. Basic machine lockdown B. Apache Configuration and Hardening C. PHP Configuration and Hardening D. Secure Practices for PHP Development E. Secure Configuration of Common PHP Applications
Slide 3: Before taking action understand the Role of the Server Who will have physical access? Who will have shell access? Will apache write to the filesystem? Will you need perl, python etc. within the OS or for apache? If possible can you limit what kind of post/ get/cookie/file payloads can be transmitted?
Slide 4: Basic Lockdown Turn off unused services, update the machine regularly, use recommended configuration files etc. Enable logwatch or logcheck and actually read the reports. Enable a well configured file integrity checker Configure iptables – Ports 22, 80, 443 tomcat?
Slide 5: Lockdown Continued Possibly survive a SYN flood attack In /etc/sysctl.conf set net.ipv4.tcp_syncookies = 1 More Information: http://cr.yp.to/syncookies.html Restrict cron and at access using cron.allow and at.allow. chmod/chown /etc/cron* and /var/spool/ cron
Slide 6: Lockdown Continued Configure NTP for logfile accuracy. Filesystem lockdown: If possible set quota to “1” for apache. Especially /tmp and /var. Sessions can write to a user configured directory OR preferably a database. /var, /data, /home should be mounted nosuid,nodev,rw Is it reasonable to make /usr or /usr/local ro?
Slide 7: Securing Apache
Slide 8: Configuring Apache Turn off any unnecessary capabilities. Unfortunately many things are on by default. Before making changes, research potential exploits …especially in the context of the machine’s services. Look into alternatives Example: If running php, use it instead of server side includes. <?php include ‘footer.html’; ?> XBitHack not necessary
Slide 9: More Configuration Options Remove /var/www/ directories to protect identity. Create custom /var/www/error files
Slide 10: mod_dosevasive Easy to configure Can help evade DoS attacks by blocking ip addresses or URLs temporarily. Blocks if: Requests are made for the same page more than X times per second per host More than X concurrent requests on the same child per second are made First sends 403 error then blacklists. Can log to syslog and send email. Can also communicate with firewall or router and execute system commands.
Slide 11: Example Configuration LoadModule dosevasive20_module modules/mod_dosevasive20.so <IfModule mod_dosevasive20.c> DOSHashTableSize 3097 DOSPageCount 2 DOSPageInterval 1 DOSSiteCount 50 DOSSiteInterval 1 DOSBlockingPeriod 10 DOSEmailNotify admin@domain.com DOSLogDir "/tmp/mod_dosevasive“ (make writable by apache only) </IfModule>
Slide 12: mod_security Very Powerful Can be tricky to configure. Lots of testing. Especially useful if web server runs a small amount of applications.
Slide 13: mod_security Features Filters requests before apache. Filters all requests including post payloads and SSL. Understands the http protocol, allowing fine tuning. Complete logging, including post data. Custom rules using regular expressions can be applied at the virtual host level.
Slide 14: More mod_security features Upon “catch” can filter, email, log, redirect, send error code, or execute system binary. Can execute action upon file upload. Example – virus scan. Easier and better apache chrooting. No modules or libraries needed. Logs already open. One Line: SecChrootDir /chroot/apache Can use snort web attack signatures Rules are created and posted for web application vulnerabilities. Can change the identity of the web server in the http header without editing the source. Finger printing still works though.
Slide 15: Example mod_security Configuration <IfModule mod_security.c> SecFilterEngine On # Prevent OS specific keywords #index.php? include=filename SecFilter /etc/passwd # Prevent path traversal (..) attacks SecFilter "\.\./" # Very crude filters to prevent SQL injection attacks SecFilter "delete[[:space:]]+from" SecFilter "insert[[:space:]]+into" SecFilter "select.+from" </IfModule>
Slide 16: Scanning your server Nmap Nessus www.nessus.org CIS Linux Benchmark Scan http://www.cisecurity.org/bench_linux.html
Slide 17: PHP Security
Slide 18: Types of PHP Attacks Command execution and/or writing to the filesystem. Sql injection Session Hijacking Cross Site Scripting (xss) Cross Site Request Forgeries (CSRF) Session reading/predicting
Slide 19: Securing PHP Default php.ini < V.4.8 ; WARNING ; ; This is the default settings file for new PHP installations. ; By default, PHP installs itself with a configuration suitable for ; development purposes, and *NOT* for production purposes. Newer installs are better. Many php applications are installed with a default php.ini. Therefore vulnerabilities can be exploited.
Slide 20: Secure PHP Settings Recommended configurations display_errors = Off (turn on with ini_set or .htaccess) log_errors = On error_reporting = E_ALL (better error reporting) session.save_path=/opt/php/session (Should be specified by the user. Where /opt has no apache quota) session.gc_maxlifetime=600 (ten minutes of inactivity)
Slide 21: More Settings magic_quotes_gpc = Off Escapes incoming get/post/cookie data, but for what application/database. Broken Crutches. Better to use specific php functions. More later…
Slide 22: More Settings register_globals = Off Never turn on Too easy to write insecure code Auto initializes variables from Get/Post/Cookie data URL= index.php?administrator=xyz <?php if (isset($administrator)) { $authorized = true; } ?>
Slide 23: More Settings safe_mode = On (enable if possible) safe_mode_gid = On (enable if possible) Especially useful in Highly Critical attacks. Can not see files not owned by script owner. Can not execute files not owned by script owner.
Slide 24: Developing Best Practices Develop with security and production in mind. Form strict policies concerning how data is sanitized and at what stage. $_GET, $_COOKIE, $_POST should always be sanitized according to where it’s going not where it came from. Mysql = mysql_real_escape_string() Postgres = pg_escape_string () The P.E.A.R. DB class handles database data with “?” replacements. To browser = htmlentities () or strip_tags() To Shell = escapeshellcmd()
Slide 25: To Remove Javascript and reduce XSS attacks Use preg_replace() on … javascript: onclick ondblclick onmousedown onmouseup onmouseover onmousemove onmouseout onkeypress onkeydown onkeyup
Slide 26: Developing Best Practices cont. Form strict policies concerning sessions. (storage, timeouts, session id length, etc.) If on a multiuser machine make a custom session.save_path or save session data to a database. Use session_regenerate_id() to prevent fixation. Especially after privilege escalation.
Slide 27: Developing Best Practices cont. Securing Includes Place them outside of document root. ini_set("include_path",".:/home/user/libs"); But, if you have to place them in root… End them in .php, so source is not revealed. Ex. database.inc.php <Files ~ "\.inc$"> Order allow,deny Deny from all </Files>
Slide 28: Where to put db_connect.inc.php Not in document root. If possible, make it non-world readable. Apache group readable.
Slide 29: Web Applications
Slide 30: Secure Configuration of Common PHP Applications phpMyAdmin Protect config.inc.php if db access is “config” If possible use mod_cas If using http authentication force ssl using mod_rewrite RewriteRule ^/$ /index.php RewriteCond %{SERVER_PORT}!443$ RewriteRule ^(.*) https://host.com:443$1 [R=301,L]
Slide 31: Secure Configuration of Common PHP Applications phpbb If configuring remotely via the web, use ssl. Sanity.A worm attacked a flaw that allowed for system calls to be sent using GET vars. Evil PHP: <?php $term = urldecode($_GET['sterm']); ?> $_GET is decoded once by php then again by urldecode. The second time quotes or other harmful symbols can be decoded and applied to system(). Assuming no magic quotes would have prevented the problem using escapecmd().
Slide 32: Secure Configuration of Common PHP Applications Gallery Verify that gallery has written to the .htaccess and config.php file after install. Then: chmod 644 .htaccess chmod 644 config.php chmod 400 setup
Slide 33: Secure Configuration of Common PHP Applications phpnuke Move config.php outside of DocumentRoot Edit mainfile.php to path of moved config.php.
Slide 34: Web Applications When installing free web applications always be aware of security advisories. Maintain a backup of your database. Practice restoring the database. Be familiar with how to update the application. If possible always use mod_cas. Especially with tools like phpMyAdmin.
Slide 35: Questions?

   
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