[ci skip] Try to mitigate BREACH attacks against CSRF tokens
diff --git a/system/helpers/form_helper.php b/system/helpers/form_helper.php
index fc7d2a6..a49eea8 100644
--- a/system/helpers/form_helper.php
+++ b/system/helpers/form_helper.php
@@ -90,12 +90,6 @@
$form = '<form action="'.$action.'"'.$attributes.">\n";
- // Add CSRF field if enabled, but leave it out for GET requests and requests to external websites
- if ($CI->config->item('csrf_protection') === TRUE && strpos($action, $CI->config->base_url()) !== FALSE && ! stripos($form, 'method="get"'))
- {
- $hidden[$CI->security->get_csrf_token_name()] = $CI->security->get_csrf_hash();
- }
-
if (is_array($hidden))
{
foreach ($hidden as $name => $value)
@@ -104,6 +98,41 @@
}
}
+ // Add CSRF field if enabled, but leave it out for GET requests and requests to external websites
+ if ($CI->config->item('csrf_protection') === TRUE && strpos($action, $CI->config->base_url()) !== FALSE && ! stripos($form, 'method="get"'))
+ {
+ // Prepend/append random-length "white noise" around the CSRF
+ // token input, as a form of protection against BREACH attacks
+ if (FALSE !== ($noise = $CI->security->get_random_bytes(1)))
+ {
+ list(, $noise) = unpack('c', $noise);
+ }
+ else
+ {
+ $noise = mt_rand(-128, 127);
+ }
+
+ // Prepend if $noise has a negative value, append if positive, do nothing for zero
+ $prepend = $append = '';
+ if ($noise < 0)
+ {
+ $prepend = str_repeat(" ", abs($noise));
+ }
+ elseif ($noise > 0)
+ {
+ $append = str_repeat(" ", $noise);
+ }
+
+ $form .= sprintf(
+ '%s<input type="hidden" name="%s" value="%s" />%s%s',
+ $prepend,
+ $CI->security->get_csrf_token_name(),
+ $CI->security->get_csrf_hash(),
+ $append,
+ "\n"
+ );
+ }
+
return $form;
}
}