Shubham Sharma

1. Cross-Site Scripting
Attacks
on Current Web
Applications

2. 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.)

3. 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.

4. 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.

6. Non-Persistent XSS Attack

7.  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.

9. Persistent XSS Attacks

10. 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.

12. BACHAA V !!!

13. Actual Demonstration

14. No Protection

15. 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.

16. Preg Match
 Performs a regular expression match.

17. 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.

18. htmlspecialchars

20. 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.

23. 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/

24. Usage of ENT_IGNORE

25. 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.

26. ID
Flags
FILTER_SANITIZE_EM
AIL
FILTER_SANITIZE_EN
CODED
Remove all characters
except letters, digits
and !#$%&'*+/=?^_`{|}~@.[].
FILTER_FLAG_STRIP_LOW
,
FILTER_FLAG_STRIP_HIG
H,
FILTER_FLAG_ENCODE_L
OW,
FILTER_FLAG_ENCODE_HI
GH
URL-encode string,
optionally strip or
encode special
characters.
Apply addslashes().
FILTER_SANITIZE_MAGIC
_QUOTES
FILTER_SANITIZE_NUMB
ER_FLOAT
Description
FILTER_FLAG_ALLOW_FR
ACTION,
FILTER_FLAG_ALLOW_TH
Remove all characters
except digits, +- and
optionally .,eE.

27. ID
Flags
FILTER_SANITIZE
_NUMBER_INT
Description
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
HTMLescape '"<>& and
characters with ASCII
value less than 32,
optionally strip or
encode other special
characters.
FILTER_SANITIZE
_STRING
FILTER_FLAG_NO_ENCODE_Q
UOTES,
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.

28. ID
Flags
FILTER_SANITIZE_UR
L
Description
Remove all characters
except letters, digits
and $_.+!*'(),{}|^~[]`<>
#%";/?:@&=.
FILTER_UNSAFE_RA
W
FILTER_FLAG_STRIP_LOW Do nothing, optionally
,
strip or encode special
FILTER_FLAG_STRIP_HIG characters.
H,
FILTER_FLAG_ENCODE_L
OW,
FILTER_FLAG_ENCODE_HI
GH,
FILTER_FLAG_ENCODE_A
MP
FILTER_SANITIZE_FU
LL_SPECIAL_CHARS
FILTER_FLAG_NO_ENCOD
E_QUOTES,
Equivalent to
callinghtmlspecialchar
s() withENT_QUOT
ES set. Encoding
quotes can be disabled

29. 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

31. Default
Information Disclosure

32. Original Contact Information
Original Code

33. How to change Contact info
 Go to :
• binariesapacheerror
• Open contact.html.var

34. Modified Code
Change contact information

35. 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'""

36. Before
After

37.  ADD/replace/change in php.ini to remove php
version disclosure
 expose_php = Off
 display_errors=Off
 register_globals = Off

39. Disable Version Disclosure
 Go to :
• binariesapacheerrorinclude
• Open bottom.html
By Default
we see this

40. Original Bottom.html file

41. Change
Bottom.html

42. My customized error page !!

43. 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.

44. Protecting bakup files
 Add in httpd.config
 TheFilesMatchdirective only looks at the last part of
the full filename

45. 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.

46. How to Disable Directory
Listings in Apache
 Navigate to your Apache config file (httpd.conf)
 Find – “Options FollowSymLinks Indexes”
 Replace by – “Options FollowSymLinks”
 Done

47.  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.

49. 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).

51. 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.

52. References
 http://php.net/manual/en/filter.filters.sanitize.php
 http://www.sitepoint.com/php-security-cross-site-
scripting-attacks-xss/

53. Emailshubham.sharma3005@gmail.com
Phone- +91-99300-53215
Thank You !!