secure coding
TRANSCRIPT
Cross-Site Scripting Attacks
on Current Web Applications
Introduction
An attacker gets control of the user’s browser in order to execute a malicious script within the context of trust of the web application’s site.
As a result, and if the embedded code is successfully executed, the attacker might then be able to access, passively or actively, to any sensitive browser resource associated to the web application (e.g., cookies, session IDs, etc.)
THREATS!!!
Everything from account hijacking, changing of user settings, cookie theft/poisoning, or false advertising is possible.
Steal cookies which can then be used to impersonate customer and have access to their data and privileges.
This is also known as Session Hijacking.
Redirect the user to another website of their
choosing. Maybe one that may be quite offensive, or one that attempts to install malware onto users computer;
Display alternate content on your own website.
History of Attacks
October 2001, -----Hotmail ---- Remote attacker was allowed to steal .NET Passport identifiers of Hotmail’s users by collecting their cookies.
October 2005, ------ MySpace, utilized by the worm Samy to propagate itself across MySpace’s user profiles.
November 2006,Orkut, was vulnerable to cookie stealing by simply posting the stealing script into the attacker’s profile.
Non-Persistent XSS Attack
User input is reflected immediately on the page by server-side scripts without proper sanitization.
To exploit, the attacker has to provide the victim with a modified URL, passing the code to be inserted as a parameter.
This attack is done by encoding data in the URL, thus disguising the injected code from the user.
Persistent XSS Attacks
Persistent XSS Attacks
When the data entered by the user are stored on the server for a certain length of time, the attack is called "persistent".
All of the website's users have access to the page where the harmful code was introduced.
Commonly found in: Contact/Feedback pages,
Log viewers, Exception handlers, Chat
applications/Forums, etc.
BACHAA V !!!
Actual Demonstration
No Protection
Data Validation
Application accepts correct data.
User data must be validated to ensure it is of the corrected type, and discarded if it doesn’t pass the validation process.
Allow a limited set of special characters.
Preg Match
Performs a regular expression match.
Output Escaping
Protects integrity of displayed/output data,
Should escape the data when presenting it to the user.
Prevents the browser from applying any unintended meaning to any special sequence of characters that may be found.
htmlspecialchars
Data Sanitization
Manipulating the data to make sure it is safe.
Removing any unwanted bits from the data and normalizing it to the correct form.
htmlentities
Converts all applicable characters to HTML entities.
Default value for this argument is ISO-8859-1 in versions of PHP prior to 5.4.0, and UTF-8 from PHP 5.4.0 onwards.
** http://coderstoolbox.net/
Usage of ENT_IGNORE
Available flags constants
ID Description
ENT_COMPAT Will convert double-quotes and leave single-quotes alone.
ENT_QUOTES Will convert both double and single quotes.
ENT_NOQUOTES Will leave both double and single quotes unconverted.
ID Flags Description
FILTER_SANITIZE_EMAIL
Remove all characters except letters, digits and !#$%&'*+-/=?^_`{|}~@.[].
FILTER_SANITIZE_ENCODED
FILTER_FLAG_STRIP_LOW,FILTER_FLAG_STRIP_HIGH,FILTER_FLAG_ENCODE_LOW,FILTER_FLAG_ENCODE_HIGH
URL-encode string, optionally strip or encode special characters.
FILTER_SANITIZE_MAGIC
_QUOTES
Apply addslashes().
FILTER_SANITIZE_NUMB
ER_FLOAT
FILTER_FLAG_ALLOW_FRACTION,FILTER_FLAG_ALLOW_THOUSAND,
Remove all characters except digits, +- and optionally .,eE.
ID Flags Description
FILTER_SANITIZE_NUMBER_INT
Remove all characters except digits, plus and minus sign.
FILTER_SANITIZE_SPECIAL_CHARS
FILTER_FLAG_STRIP_LOW,FILTER_FLAG_STRIP_HIGH,FILTER_FLAG_ENCODE_HIGH
HTML-escape '"<>& and characters with ASCII value less than 32, optionally strip or encode other special characters.
FILTER_SANITIZE_STRING
FILTER_FLAG_NO_ENCODE_QUOTES,FILTER_FLAG_STRIP_LOW,FILTER_FLAG_STRIP_HIGH,FILTER_FLAG_ENCODE_LOW,FILTER_FLAG_ENCODE_HIGH,FILTER_FLAG_ENCODE_AMP
Strip tags, optionally strip or encode special characters.
FILTER_SANITIZE_STRIPPED
Alias of "string" filter.
ID Flags Description
FILTER_SANITIZE_URL
Remove all characters except letters, digits and $-_.+!*'(),{}|\\^~[]`<>#%";/?:@&=.
FILTER_UNSAFE_RAW
FILTER_FLAG_STRIP_LOW,FILTER_FLAG_STRIP_HIGH,FILTER_FLAG_ENCODE_LOW,FILTER_FLAG_ENCODE_HIGH,FILTER_FLAG_ENCODE_AMP
Do nothing, optionally strip or encode special characters.
FILTER_SANITIZE_FULL_SPECIAL_CHARS
FILTER_FLAG_NO_ENCODE_QUOTES,
Equivalent to callinghtmlspecialchars() withENT_QUOTES set. Encoding quotes can be disabled by
Mod Security(Web Application Firewall)
Protects against attacks that target websites.
csrf_protection
session_hijacking
comment_spam
authentication_tracking
protocol_violations
sql_injection_attacks
xss_attacks
brute_force, and many more
Default Information Disclosure
Original Contact Information
Original Code
How to change Contact info
Go to :
• \binaries\apache\error
• Open contact.html.var
Change contact informationModified Code
Disable Apache Signature and/or Apache Banner
ADD in httpd.config of apache to remove apache version disclosure
ServerTokens ProductOnly
ServerTokens takes 1 argument, 'Prod', 'Major', 'Minor', 'Min', 'OS', or 'Full'""
Before After
ADD/replace/change in php.ini to remove phpversion disclosure
expose_php = Off
display_errors=Off
register_globals = Off
Disable Version Disclosure
Go to :
• \binaries\apache\error\include
• Open bottom.html
By Default we see this
Original Bottom.html file
Change Bottom.html
My customized error page !!
Stopping Sensitive file disclosure
Turn off automatic indexing.
Instruct Apache to reject all requests for files matching a series of regular expressions given below.
Goto httpd.conf file to deny access to . htaccess files.
Protecting bakup files
Add in httpd.config
TheFilesMatchdirective only looks at the last part of the full filename
Disable Directory Indexing
Listing of files like see in Windows Explorer as opposed to a web page.
Attacker can gain valuable information about your site.
Files may may include sensitive information, such as backup script files htaccess files, or text files with note.
Can allow access files outside the web root directory, leading to the stealing of system files.
How to Disable Directory Listings in Apache
Navigate to your Apache config file (httpd.conf)
Find – “Options FollowSymLinks Indexes”
Replace by – “Options FollowSymLinks”
Done
FollowSymLinks makes Apache follow system symbolic links (shortcuts, if you would) in your file system.
Indexes allows access to open folders within your file system.
Disable powerful functions in php
Disable functions that may be useful to an attacker but not necessary to the application.
Disable execution of OS commands
Open php.ini and search “disable_functions”.
Write “shell_exec “ (without comma in front of disable_functions).
Other functions
exec, passthru, shell_exec, system, proc_open, popen, curl_exec, curl_multi_exec, pcntl_exec, dl".
If the application needs to execute OS commands, it should use "pcntl_exec", because it provides better abstraction of parameters than the others.
References
http://php.net/manual/en/filter.filters.sanitize.php
http://www.sitepoint.com/php-security-cross-site-scripting-attacks-xss/
