CodeIgniter CSRF token in JSON request - json

Question

I ran into an issue with CodeIgniter / CSRF / JSON.
I am sending http POST requests to my PHP backend with the Content-Type "application/json. The payload is JSON data. Along with the data, I pass the CSRF token that is generated and stored in the CSRF cookie. With a standard POST FORM request, it works just fine, but when sending as JSON it fails.
As $_POST array is empty because of the JSON content-type, CodeIgniter fails to validate the cookie and throws an error.
How can I have CodeIgniter check JSON payload and validate my CSRF token ?

Answer 1

To fix that issue, I had to change the code of the "Security.php" file located in "system/core/".
In function "csrf_verify", replace that code:
// Do the tokens exist in both the _POST and _COOKIE arrays?
if ( ! isset($_POST[$this->_csrf_token_name], $_COOKIE[$this->_csrf_cookie_name]))
{
$this->csrf_show_error();
}
// Do the tokens match?
if ($_POST[$this->_csrf_token_name] != $_COOKIE[$this->_csrf_cookie_name])
{
$this->csrf_show_error();
}
By that code:
// Do the tokens exist in both the _POST and _COOKIE arrays?
if ( ! isset($_POST[$this->_csrf_token_name], $_COOKIE[$this->_csrf_cookie_name])) {
// No token found in $_POST - checking JSON data
$input_data = json_decode(trim(file_get_contents('php://input')), true);
if ((!$input_data || !isset($input_data[$this->_csrf_token_name], $_COOKIE[$this->_csrf_cookie_name])))
$this->csrf_show_error(); // Nothing found
else {
// Do the tokens match?
if ($input_data[$this->_csrf_token_name] != $_COOKIE[$this->_csrf_cookie_name])
$this->csrf_show_error();
}
}
else {
// Do the tokens match?
if ($_POST[$this->_csrf_token_name] != $_COOKIE[$this->_csrf_cookie_name])
$this->csrf_show_error();
}
That code first checks $_POST then if nothing has been found, it checks the JSON payload.
The ideal way of doing this would be to check the incoming request Content-Type header value. But surprisingly, it's not straight forward to do ...
If someone has a better solution, please post it here.
Cheers

Answer 2

Alternatively, you can skip the CSRF checking by adding following code on application/config/config.php below Line No. 351 (based on CI 2.1.4).
$config['csrf_expire'] = 7200; // This is line no. 351
/* If the REQUEST_URI has method is POST and requesting the API url,
then skip CSRF check, otherwise don't do. */
if (isset($_SERVER["REQUEST_URI"]) &&
(isset($_SERVER['REQUEST_METHOD']) && ($_SERVER['REQUEST_METHOD'] == 'POST') ))
{
if (stripos($_SERVER["REQUEST_URI"],'/api/') === false ) { // Verify if POST Request is not for API
$config['csrf_protection'] = TRUE;
}
else {
$config['csrf_protection'] = FALSE;
}
} else {
$config['csrf_protection'] = TRUE;
}

Answer 3

If this needs to be overridden, best to extend the Security library rather than editing the core file directly.
Create the file My_Security.php in application/core/ and add the following (from the solution above):
<?php
class My_Security extends CI_Security {
/**
* Verify Cross Site Request Forgery Protection
*
* #return object
*/
public function csrf_verify()
{
// If it's not a POST request we will set the CSRF cookie
if (strtoupper($_SERVER['REQUEST_METHOD']) !== 'POST')
{
return $this->csrf_set_cookie();
}
// Do the tokens exist in both the _POST and _COOKIE arrays?
if ( ! isset($_POST[$this->_csrf_token_name], $_COOKIE[$this->_csrf_cookie_name])) {
// No token found in $_POST - checking JSON data
$input_data = json_decode(trim(file_get_contents('php://input')), true);
if ((!$input_data || !isset($input_data[$this->_csrf_token_name], $_COOKIE[$this->_csrf_cookie_name])))
$this->csrf_show_error(); // Nothing found
else {
// Do the tokens match?
if ($input_data[$this->_csrf_token_name] != $_COOKIE[$this->_csrf_cookie_name])
$this->csrf_show_error();
}
}
else {
// Do the tokens match?
if ($_POST[$this->_csrf_token_name] != $_COOKIE[$this->_csrf_cookie_name])
$this->csrf_show_error();
} // We kill this since we're done and we don't want to
// polute the _POST array
unset($_POST[$this->_csrf_token_name]);
// Nothing should last forever
unset($_COOKIE[$this->_csrf_cookie_name]);
$this->_csrf_set_hash();
$this->csrf_set_cookie();
log_message('debug', 'CSRF token verified');
return $this;
}
}

Answer 4

As Brian write, you have to put your custom class into /application/core/ ex. My_Security.php
This is mine solution, work for me, i check the application/json content_type and request cookies.
defined('BASEPATH') OR exit('No direct script access allowed');
class MY_Security extends CI_Security {
public function csrf_verify()
{
// If it's not a POST request we will set the CSRF cookie
if (strtoupper($_SERVER['REQUEST_METHOD']) !== 'POST')
{
return $this->csrf_set_cookie();
}
/**
* mine implementation for application/json
*/
$reqHeaders = getallheaders();
$content_type = $reqHeaders["Content-Type"];
#it's a json request?
if(preg_match("/(application\/json)/i",$content_type))
{
#the check the cookie from request
$reqCookies = explode("; ",$reqHeaders["Cookie"]);
foreach($reqCookies as $c)
{
if(preg_match("/(".$this->_csrf_cookie_name."\=)/", $c))
{
$c = explode("=",$c);
if($_COOKIE[$this->_csrf_cookie_name] == $c[1])
{
return $this;
}
}
}
}
//< end
// Check if URI has been whitelisted from CSRF checks
if ($exclude_uris = config_item('csrf_exclude_uris'))
{
$uri = load_class('URI', 'core');
foreach ($exclude_uris as $excluded)
{
if (preg_match('#^'.$excluded.'$#i'.(UTF8_ENABLED ? 'u' : ''), $uri->uri_string()))
{
return $this;
}
}
}
// Do the tokens exist in both the _POST and _COOKIE arrays?
if ( ! isset($_POST[$this->_csrf_token_name], $_COOKIE[$this->_csrf_cookie_name])
OR $_POST[$this->_csrf_token_name] !== $_COOKIE[$this->_csrf_cookie_name]) // Do the tokens match?
{
$this->csrf_show_error();
}
// We kill this since we're done and we don't want to polute the _POST array
unset($_POST[$this->_csrf_token_name]);
// Regenerate on every submission?
if (config_item('csrf_regenerate'))
{
// Nothing should last forever
unset($_COOKIE[$this->_csrf_cookie_name]);
$this->_csrf_hash = NULL;
}
$this->_csrf_set_hash();
$this->csrf_set_cookie();
log_message('info', 'CSRF token verified');
return $this;
}
}