S8-Session Managment

Web Application Security (PHP)
Zakieh Alizadeh
zakiehalizadeh@gmail.com
APA Laboratory – Ferdowsi University of Mashhad

Session Management
 Description Mechanism of Cookies
 Introducing Session Management Attacks
Strategies Of Session Storage
Session Management Testing
Strategies for Secure Session Management

Mechanism of Cookies
HTTP session token
 Problem : HTTP is stateless
o Solution : HTTP Cookies
 The client usually stores cookies and sends the token as an
o HTTP cookie
o parameter in GET or POST queries.

 What is Sessions
 A session is a semi-permanent interactive information interchange, also known as
a dialogue, a conversation or a meeting, between a computer and user .
 An established communication session may involve more than one message in
each direction.
 A session is typically, but not always, stateful, meaning that at least one of the
communicating parts needs to save information.
 where the communication consists of independent requests with responses.
Such as HTTP.

Session ID
 A session identifier, session ID or session token is a piece of data that is
used in network communications (often over HTTP) to identify a session.
 A session ID is often a long, randomly generated string to decrease the
brute-force search.
 The reason to use session tokens is :
o client only has to handle the identifier (a small piece of data that hasn’t
security risk) - all session data is stored on the server and is not
transmit

HTTP session token

Http Cookies
HTTP Cookies
 The following is a list of the attributes that can be set for each cookie :
o secure - only send the cookie if the request is being sent over a
secure channel such as HTTPS.
o HttpOnly - it does not allow the cookie to be accessed via a client side
script such as JavaScript.
• Note that not all browsers support this functionality.
o domain - compare against the domain of the server in which the URL
is being requested

Http Cookies
HTTP Cookies
 The following is a list of the attributes that can be set for each cookie :
o path - In addition to the domain, the URL path can be specified for
which the cookie is valid. If the domain and path match, then the
cookie will be sent in the request.
o expires - This attribute is used to set persistent cookies, since the
cookie does not expire until the set date is exceeded.

Http Cookies
 HTTP Cookies : PHP function
 session_set_cookie_params() The effect of this function only lasts for the duration of
the script.
 Thus, you need to call it for every request and before session_start() is called.
 This function updates the runtime ini values of the corresponding PHP ini configuration
session_set_cookie_params ($lifetime , $path , $domain, $secure = false , $httponly = false)

Http Cookies
 HTTP Cookies : PHP function
 setcookie() defines a cookie to be sent along with the rest of the HTTP headers.
 Like other headers, cookies must be sent before any output from your script (this is a
protocol restriction).
 Once the cookies have been set, they can be accessed on the next page load with the
$_COOKIE
Setcookie ( $name , $value , $expire = 0 , $path , $domain , $secure =false , $httponly = false )

Session Management
Session management
 session management is the process of keeping track of a user's activity
across sessions of interaction with the system.

Session Management
 Description Mechanism of Cookies
 Introducing Session Management Attacks

Session Attacks
Sessions Attack
 Session Fixation
 Session Brute-Forcing
 Session Hijacking
 Session Poisoning

Sessions Attack
Session fixation
 session fixation attacks allows one person to fixate (set) another person's
session identifier (SID).
 Hacker abtains valid session witout hijacking or sniffing, he fix valid
session for victim.
 Most rely on session identifiers being accepted from URLs (query string)
or POST data.

Sessions Attack
Session fixation
 Session fixation vulnerabilities occur when:
 A web application authenticates a user without first invalidating the
existing session ID, thereby continuing to use the session ID already
associated with the user.
 An attacker is able to force a known session ID on a user so that, once the
user authenticates, the attacker has access to the authenticated session.

Sessions Attack
Session fixation
1
3
2
4
No new
Cookie Set
In HTTP
Response
successfully authenticate request

Sessions Attack
Session fixation

Sessions Attack
Session fixation : Countermeasures
 Do not accept session identifiers from GET / POST variables
 Accept only server-generated SIDs
 Logout function
 Destroy session if Referrer is suspicious
 Time-out old SIDs
 Verify that additional information is consistent throughout session
 User Agent

Sessions Attack
Session fixation : Defense in Depth
 Enable HTTPS (to protect against other problems)
 Correct configuration (do not accept external SIDs, set time-out, etc.)
o Ini_set(“session_use_only_cookie”,1)
 Perform session_regeneration, support log-out, etc.

Sessions Attack
Session hijacking
 session hijacking is the exploitation of a valid sessionID to gain unauthorized
access to information or services in a computer system.

Sessions Attack
Session hijacking : Methods
 Session fixation
 Session sidejacking
o where the attacker uses packet sniffing
o Many web sites use SSL encryption for login pages to prevent
attackers from seeing the password, but do not use encryption for the
rest of the site once authenticated.


Sessions Attack
Session hijacking : Methods
 obtaining the file or memory contents of the appropriate part of either
the user's computer or the server.
 Cross-site scripting, where the attacker tricks the user's computer into
running code which is treated as trustworthy because it appears to
belong to the server, allowing the attacker to obtain a copy of the cookie
or perform other operations.

Sessions Attack
Session hijacking : Countermeasures
 Provide a method for users to log out of the application.
o Logging out button should clear
o all session state and remove or invalidate any residual cookies.
 Set short expiry times on persistent cookies, no more than a day.
 Do not store session tokens in the URL or other trivially modified data
entry point.

Sessions Attack
Brute Force Session Identifier
 Session tokens are generated in
o a predictable fashion
o key space that is too small to prevent guessing a token in reasonable
time.
o The application does not detect and prevent session brute forcing
attempts.
 A session ID must not be valid over two currently active SSL connections
at the same time.

Sessions Attack
Brute Force SessionID: Countermeasures
 Session identifiers should be at least 128 bits(32byte) long to prevent
brute-force session guessing attacks.
 Limit the number of unique session tokens you see from the same IP
address (ie 20 in thelast five minutes).
 Use Strong Session Cryptographic Algorithms
o Use Framework session management impelemention

Sessions Attack
Session poisoning
 This should actually be called session injection, as it is just one more
variable injection type of attack. If you allow user input into session
variables, make sure you validate the data.
 Typically a server application that is vulnerable to this type of exploit will
copy user input into session variables.

Sessions Attack
Session poisoning :Example
 Exploiting ambiguous or dual use of same session variable
 Exploiting scripts allowing writes to arbitrary session variables
$var = $_GET["something"];
$_SESSION["$var"] = $var2;
vulnerable.php?something=SESSION_VAR_TO_POISON

Sessions Attack
Session poisoning :Example
 Session poisoning attacks enabled by php.ini: register_globals = on
 It is possible for attacker to cause both conditions to be false.
 php.ini is misconfigured (register_globals = on), which allows $var default
value to be controlled by GPC (GET, POST, or COOKIE) input.
if ($condition1) { $var = 'SOMETHING'; };
if ($condition2) { $var = 'OTHER'; };
$_SESSION["$var"] = $var2;

Session Storage
Session Storage
 Sessions data can Store in :
o Files (on server)
o database.
 Sessions data that Storage in Files
o Better performance ,But weak security
 Sessions data that Storage in Database
o Better security,But weak performance

Session Management
Session Management Testing

Session Management Testing
Session Management Testing
Test Desc
Testing for Session
Management Schema
 1-cookie collection: 2-cookie reverse engineering 3- cookie
manipulation
 The session tokens tested for their randomness, uniqueness,
resistance to statistical and cryptographic analysis
Testing for Cookies
attributes
Testing for secure or httponly setting
Are all Set-Cookie directives tagged as Secure?
What Expires= times are used on persistent cookies
Testing for Session
Fixation  no new cookie has been issued upon a successful authentication

Session Management Testing
Session Management Testing
Test Desc
Testing for Exposed
Session Variables
How are Session IDs transferred? E.g., GET, POST, Form Field
Are Session IDs always sent over encrypted transport by default?
Testing for CSRF
URL being tested; for example
 u = http://www.example.com/action
build an html page containing the http request referencing URL u
Regeneration of
Session Tokens
•Note the Session ID at the start and after every significant test
transaction.
If the session ID never changes,Application be at risk

Session Management
Strategies for Secure Session Management

Session Management
Session Management : Countermeasures
 Avoid Weak Session Cryptographic Algorithms
 Use Appropriate Key Space
 Impelement Session Time-out
 Regeneration of Session Tokens
o prior to any significant transaction
o after a certain number of requests
o after as a function of time, say every 20 minutes or so.
o Problem : when using third party software

Session Management
Session Management : Countermeasures
 Using framework implementation session management.
 Authorization and role data should be stored on the server side only.
 Presentation flags (such as theme or user language) can belong in
cookies.
 Tie the session to a particular browser by using a hash of the server-side
IP address.

S8-Session Managment

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