Secure Programming With The Zend Framework

http://www.sektioneins.de

Secure Programming with the Zend-Framework Stefan Esser <[email protected]>

June 2009 - Amsterdam

Who I am?

Stefan Esser

•

from Cologne / Germany

•

Information-Security since 1998

•

PHP Core Developer since 2001

•

Month of PHP Bugs and Suhosin

•

Head of Research and Development at SektionEins GmbH

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Part I Introduction

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Introduction

• Using the Zend-Framework got very popular in the last years • Growing request of security for Zend-Framework based applications • Books/Talks/Seminars concentrate on secure programming of PHP applications without a framework

• Using a framework requires different ways to implement protections • Some frameworks come with their own security features

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Topics

• Authentication • Input Validation and Input Filtering • SQL Security • Cross Site Request Forgery (CSRF) Protection • Session Management Security • Cross Site Scripting (XSS) Protection

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Part II Authentication

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Classic Applications vs. Zend-Framework

• Zend-Framework applications usually use a MVC design with dispatcher

Dispatcher

• Classic applications usually use neither a MVC design, nor a dispatcher

• without dispatcher every reachable script

Controller

must implement or embed authentication

• classic approach is error-prone • often scripts exists that forget to implement the authentication

View

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Model

Central Authentication in Controller • Deriving the Zend_Controller_Action • Authentication implemented in init() method • Attention: if a controller has an own init() method then method of the parent class must be called class My_Controller_Action extends Zend_Controller_Action { /** * Init function * * First check if this is a logged in user, ... */ public function init() { $isLoggedIn = true; try { My_Auth::isLoggedIn(); } catch (My_Auth_UserNotLoggedInException $e) { $isLoggedIn = false; } ... }

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Part III Input Validation and Input Filtering

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Accessing Request Parameters (I)

• Traditionally PHP applications access user input directly ➡ $_GET, $_POST, $_COOKIE, $_REQUEST, $_SERVER, $_ENV, $_FILES

• Form of access also possible in Zend-Framework, but not usual ➡ Input validation and input filtering not directly portable from traditional PHP applications

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Accessing Request Parameters (II) • Access via request object Zend_Controller_Request_Http • Either via methods or magic properties • Access is unfiltered - only raw data • Access via magic property in the following order 1. internal parameter array 2. $_GET 3. $_POST 4. $_COOKIE

$message = $this->getRequest()->message;

5. $_SERVER 6. $_ENV

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Accessing Request Parameters (III)

• function getQuery($key = null, $default = null) • function getPost($key = null, $default = null) • function getCookie($key = null, $default = null) • function getServer($key = null, $default = null) • function getEnv($key = null, $default = null) • wrapper around $_GET / $_POST / $_COOKIE / $_SERVER / $_ENV with the possibility to return a default value

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Accessing Request Parameters (IV)

• function getParam($key = null, $default = null) • gets parameters from the internal parameter array and from $_GET and $_POST or returns the default value

• parameter sources can be configured ($_GET / $_POST) • similar to $_REQUEST without $_COOKIE

• function getParams($key = null, $default = null) • gets all parameters from the internal parameter array, $_GET and $_POST • in case of double entries, later entries will overwrite the earlier entries

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Validation with Zend_Validate • Validators to validate parameters • Zend-Framework comes with a set of validators Alnum, Alpha, Barcode, Between, Ccnum, Date, Digits, EmailAddress, Float, GreaterThen, Hex, Hostname, Iban, InArray, Int, Ip, LessThan, NotEmpty, Regex, StringLength getRequest()->getPost('email', '[email protected]'); $validator = new Zend_Validate_EmailAddress(); if ($validator->isValid($email)) { // email seems valid } else { // email seems invalid; Outputting the reasons foreach ($validator->getMessages() as $message) { echo "$message\n"; } } ?>

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Chaining Validators

• for complex validations own validators can be implemented • it is however possible to combine validators in validator chains addValidator(new Zend_Validate_StringLength(6, 12)) ->addValidator(new Zend_Validate_Alnum()); // Validation of "username" if ($validatorChain->isValid($username)) { // "username" is valid } else { // "username" is invalid; Outputting the reasons foreach ($validatorChain->getMessages() as $message) { echo "$message\n"; } } ?>

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Filtering with Zend_Filter

• Filtering of parameters is done with filters • Zend-Framework comes with a set of pre defined filters Alnum, Alpha, BaseName, Callback, Decrypt, Digits, Dir, Encrypt, Htmlentities, Int, StripNewlines, RealPath, StringToUpper, StringToLower, StringTrim, StripTags

getRequest()->getPost('message', ''); $filter = new Zend_Filter_StripTags(); // remove all tags $message = $filter->filter($message); ?>

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Chaining Filters

• for complex filtering own filters can be implemented • it is however possible to combine filters in filter chains addFilter(new Zend_Filter_Alpha()) ->addFilter(new Zend_Filter_StringToLower()); // Filtering "username" $username = $filterKette->filter($username); ?>

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Inputvalidation/-filtering in Forms (I) • ZF-Forms use validators and filters automatically • they are attached to Zend_Form_Element objects • and can be chained as wished // create name element $name = $form->createElement('text', 'name', array('size' => 40, 'maxlength' => 40)); $name->addValidator('Alpha') ->addValidator('StringLength', false, array(1, 40)) ->setLabel('Name') ->setRequired(true); // create message element $message = $form->createElement('textarea', 'message', array('rows' => 6, 'cols' => 40)); $message->setLabel('Message') ->setRequired(true) ->addFilter('StripTags'); // create submit button $submit = $form->createElement('submit', 'send'); $submit->setLabel('send'); // add all elements to the form $form->addElement($name)->addElement($message)->addElement($submit);

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Inputvalidation/-filtering in Forms (II)

• Form is validated in the action handler // checking form data for validity if (!$form->isValid($this->getRequest()->getPost())) { // submit varibales to view $this->view->form = $form; $this->view->title = "Form 1";

}

// stop processing return $this->render('form');

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Validation and Filtering with Zend_Filter_Input • is a framework for validation and filtering complete arrays • applies defined filter and validation ruleset to supplied data • allows validation of all user input automatically $filters = array( '*' => 'StringTrim', 'month' => 'Digits' ); $validators = array( 'month' => array( new Zend_Validate_Int(), new Zend_Validate_Between(1, 12) ) ); $params = $this->getRequest()->getParams(); $input = new Zend_Filter_Input($filters, $validators, $params); if ($input->isValid()) { echo "OK\n"; }

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Part IV SQL Security

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SQL Security - Traditionally

• Traditional PHP Applications • use PHP‘s database extensions directly • use their own database abstraction layer • use PDO

• lots and lots of different escaping functions • escaping only supports data not identifiers • partially support for prepared statements

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Databaseaccess in Zend-Framewok Applications

➡ Zend-Framework offers different APIs for handling queries • Zend_Db • Zend_Db_Statement • Zend_Db_Select • Zend_Db_Table

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Zend_Db - Queries (I) • function query($sql, $bind = array()) • uses prepared statement internally • SQL-Injection still possible if $sql is dynamically created • function fetchAll($sql, $bind = array(), $fetchMode = null) • all „fetch“ methods use prepared statements internally • SQL-Injection still possible if $sql is dynamically created

fetchAll($sql, $params); ?>

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Zend_Db - Queries (II)

• function insert($table, array $bind) • internally uses prepared statements • SQL-Injection not possible

• function update($table, array $bind, $where = '') • uses partially prepared statements • SQL-Injection still possible if $where is dynamically created

• function delete($table, $where = '') • SQL-Injection still possible if $where is dynamically created

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Zend_Db - Escaping

• function quote($value, $type = null) • applies the correct escaping - one function not many • ATTENTION: also puts strings in quotes

• function quoteIdentifier($ident, $auto=false) • applies escaping for identifiers • a function not available to traditional PHP applications • ATTENTION: also puts strings in quotes

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Zend_Db_Select • used to dynamically build SELECT statements • uses partially prepared statements • SQL-Injectionen still possible when wrongly used • vulnerable through: WHERE / ORDER BY // Build this query: // SELECT product_id, product_name, price // FROM "products" // WHERE (price < 100.00 OR price > 500.00) // AND (product_name = 'Apple') $minimumPrice = 100; $maximumPrice = 500; $prod = 'Apple'; $select = $db->select() ->from('products', array('product_id', 'product_name', 'price')) ->where("price < $minimumPrice OR price > $maximumPrice") ->where('product_name = ?', $prod);

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Part V Cross Site Request Forgery (CSRF) Protection

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Cross Site Request Forgery (CSRF) Protection

• Protections against CSRF attacks are usually based on secret, session depended form tokens

• Zend-Framework offers Zend_Form_Element_Hash which is a secret token with built-in validator

• HTML forms can be secured against CSRF attacks by just adding the form element to the form

$form->addElement('hash', 'csrf_token', array('salt' => 's3cr3ts4ltG%Ek@on9!'));

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Automatic CSRF Protection

• normally protection must be added manually • by deriving Zend_Form it is possible to create an own form class that automatically comes with CSRF protection addElement('hash', 'csrf_token', array('salt' => get_class($this) . 's3cr3t%Ek@on9!')); } } ?>

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Token Algorithm

• Token algorithm could be improved

• avoid mt_rand() • more entropy

• but it is safe enough (for now)

/** * Generate CSRF token * */ protected function _generateHash() { $this->_hash = md5( mt_rand(1,1000000) . $this->getSalt() . $this->getName() . mt_rand(1,1000000) ); $this->setValue($this->_hash); }

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Part VI Session Management Security

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Session Management Configuration • Configuration has big influence on security • to safeguard SSL applications set the secure flag • use an own session id for each application • harden the session cookie against XSS with the httpOnly flag • define the maximal lifetime

=> => => => =>

true, 'mySSL', '/sessions/mySSL', true, 15 * 60

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Session Fixation and Session Hijacking

• Session Fixation • is harder in case of session validation / strict session handling • but is only stopped by regenerating the session id after each change in status Zend_Session::regenerateId();

• should be added directly into the login functionality

• Session Hijacking • there is only one real protection - SSL • httpOnly cookies protect against session id theft by XSS • session validation only of limited use Stefan Esser • Secure Programming with the Zend-Framework • June 2009 •  34

Session Validation (I) • recognizes a valid session by checking certain additional information stored in the session

• often recommended as protection against session fixation/hijacking - but doesn‘t make much sense

• Zend-Framework supports session validators to validate sessions • Zend_Session_Validator_HttpUserAgent

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Session Validation (II)

• Attention checking additional information can cause trouble • User-agent HTTP header checking is dead since Internet Explorer 8 • Accept HTTP header checks have always been a problem with Microsoft Internet Explorer

• Checking the client‘s IP address is a problem when big proxy farms are used (big companies/ISPs)

➡ possible to limit to class C/B/A networks ➡ but useful for SSL applications

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Session Validation - Validating Client‘s IP Address setValidData( (isset($_SERVER['REMOTE_ADDR']) ? $_SERVER['REMOTE_ADDR'] : null) ); } /** * Validate() - this method will determine if the client's remote addr * matches the remote address we stored when we initialized this variable. * * @return bool */ public function validate() { $currentBrowser = (isset($_SERVER['REMOTE_ADDR']) ? $_SERVER['REMOTE_ADDR'] : null); }

return $currentBrowser === $this->getValidData();

} ?> Stefan Esser • Secure Programming with the Zend-Framework • June 2009 •  37

Part VII Cross Site Scripting (XSS) Protection

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XSS in Zend-Framework Applications • Symfony supports automatic output escaping • Zend-Framework doesn‘t support such automagic • preventing XSS is job of the programmer • XSS occurs in the „view“ part <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">

headline; ?>

• link; ?>">Link 1

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Protecting against XSS (I)

• Two alternative traditional protections 1. Encoding before echoing <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">

escape($this->headline); ?>

• link); ?>">Link 1

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Protecting against XSS (II)

• Two alternative traditional protections 2. Encoding when assigning template variables

$entityFilter = new Zend_Filter_HtmlEntities(); $urlFilter = new My_Filter_Url(); $this->view->title = $this->escape("Page 1"); $this->view->headline = $entitiyFilter->filter($this->getRequest()->getPost('link')); $this->view->link = $urlFilter->filter($this->getRequest()->getPost('link'));

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Protecting with Zend_View_Helper • preventing XSS is error prone - one XSS for every forgotten encoding • automatically scanning for forgotten escaping is hard • directly echoing variables should be forbidden (e.g. with Bytekit + pre-commit-hook) • output only via Zend_View_Helper • preventing XSS becomes job of Zend_View_Helper

Your Email: formText('email', '[email protected]', array('size' => 32)) ?>

Your Country: formSelect('country', 'us', null, $this->countries) ?>

Would you like to opt in? formCheckbox('opt_in', 'yes', null, array('yes', 'no')) ?>

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Automatic Escaping by deriving Zend_View • all output goes through Zend_View • deriving Zend_View allows automatic encoding • e.g. by overloading __set() and __get() • Attention: Encoding must be context sensitive (e.g.: javascript: Links) public function __get($key) { if (isset($this->_params[$key])) { return($this->escape($this->_params[$key])); } return null; } public function __set($key, $val) { $this->_params[$key] = $val; }

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Thank you for listening...

Questions ? http://www.sektioneins.de

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