[ci skip] Protect CSRF verification from timing side-channel attacks

1 files changed, 8 insertions, 6 deletions

diff --git a/system/core/Security.php b/system/core/Security.php
index d198b663b..585ed90ec 100644
--- a/system/core/Security.php
+++ b/system/core/Security.php
@@ -224,12 +224,9 @@ class CI_Security {
 			}
 		}
 
-		// 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();
-		}
+		// Check CSRF token validity, but don't error on mismatch just yet - we'll want to regenerate
+		$valid = isset($_POST[$this->_csrf_token_name], $_COOKIE[$this->_csrf_cookie_name])
+			&& hash_equals($_POST[$this->_csrf_token_name], $_COOKIE[$this->_csrf_cookie_name]);
 
 		// We kill this since we're done and we don't want to pollute the _POST array
 		unset($_POST[$this->_csrf_token_name]);
@@ -245,6 +242,11 @@ class CI_Security {
 		$this->_csrf_set_hash();
 		$this->csrf_set_cookie();
 
+		if ($valid !== TRUE)
+		{
+			$this->csrf_show_error();
+		}
+
 		log_message('info', 'CSRF token verified');
 		return $this;
 	}