Implemented page referal verification mechanism. (Secunia Advisory SA34627)

doc/ChangeLog

@@ -322,6 +322,7 @@ Version 1.5.2 - SVN
   - Fixed broken RFC1918 reference in contrib/.htaccess and doc/.htaccess (#2798839).
   - Stop using deprecated ereg functions. (#2820952)
   - Remove personal data from Message ID seed. (#880029/847107)
+  - Implemented page referal verification mechanism. (Secunia Advisory SA34627)
 
 Version 1.5.1 (branched on 2006-02-12)
 --------------------------------------

functions/auth.php

@@ -24,13 +24,44 @@
  * and PAGE_NAME in session and returns false. POST information is saved in
  * 'session_expired_post' variable, PAGE_NAME is saved in 'session_expired_location'.
  *
+ * This function optionally checks the referrer of this page request.  If the
+ * administrator wants to impose a check that the referrer of this page request
+ * is another page on the same domain (otherwise, the page request is likely
+ * the result of a XSS or phishing attack), then they need to specify the
+ * acceptable referrer domain in a variable named $check_referrer in
+ * config/config.php (or the configuration tool) for which the value is
+ * usually the same as the $domain setting (for example:
+ *    $check_referrer = 'example.com';
+ * However, in some cases (where proxy servers are in use, etc.), the
+ * acceptable referrer might be different.  If $check_referrer is set to
+ * "###DOMAIN###", then the current value of $domain is used (useful in
+ * situations where $domain might change at runtime (when using the Login
+ * Manager plugin to host multiple domains with one SquirrelMail installation,
+ * for example)):
+ *    $check_referrer = '###DOMAIN###';
+ * NOTE HOWEVER, that referrer checks are not foolproof - they can be spoofed
+ * by browsers, and some browsers intentionally don't send them, in which
+ * case SquirrelMail silently ignores referrer checks.  
+ *
  * Script that uses this function instead of is_logged_in() function, must handle user
  * level messages.
  * @return boolean
  * @since 1.5.1
  */
 function sqauth_is_logged_in() {
-    if ( sqsession_is_registered('user_is_logged_in') ) {
+
+    global $check_referrer, $domain;
+    if (!sqgetGlobalVar('HTTP_REFERER', $referrer, SQ_SERVER)) $referrer = '';
+    if ($check_referrer == '###DOMAIN###') $check_referrer = $domain;
+    if (!empty($check_referrer)) {
+        $ssl_check_referrer = 'https://' . $check_referrer;
+        $check_referrer = 'http://' . $check_referrer;
+    }
+    if (sqsession_is_registered('user_is_logged_in')
+     && (!$check_referrer || empty($referrer)
+      || ($check_referrer && !empty($referrer)
+       && (strpos(strtolower($referrer), strtolower($check_referrer)) === 0
+        || strpos(strtolower($referrer), strtolower($ssl_check_referrer)) === 0)))) {
         return true;
     }
 

include/init.php

@@ -118,7 +118,7 @@ if(!empty($_SERVER['UNIQUE_ID'])) {
 }
 
 $seed .= uniqid(mt_rand(),TRUE);
-$seed .= implode( '', stat( __FILE__) );
+$seed .= implode('', stat( __FILE__));
 
 // mt_srand() uses an integer to seed, so we need to distill our
 // very large seed to something useful (without taking a sub-string,
@@ -571,16 +571,28 @@ switch (PAGE_NAME) {
 
 
         /**
-         * Check if we are logged in
+         * Check if we are logged in and does optional referrer check
          */
         require(SM_PATH . 'functions/auth.php');
 
-        if ( !sqsession_is_registered('user_is_logged_in') ) {
+        global $check_referrer, $domain;
+        if (!sqgetGlobalVar('HTTP_REFERER', $referrer, SQ_SERVER)) $referrer = '';
+        if ($check_referrer == '###DOMAIN###') $check_referrer = $domain;
+        if (!empty($check_referrer)) {
+            $ssl_check_referrer = 'https://' . $check_referrer;
+            $check_referrer = 'http://' . $check_referrer;
+        }
+        if (!sqsession_is_registered('user_is_logged_in')
+         || ($check_referrer && !empty($referrer)
+          && strpos(strtolower($referrer), strtolower($check_referrer)) !== 0
+          && strpos(strtolower($referrer), strtolower($ssl_check_referrer)) !== 0)) {
 
             // use $message to indicate what logout text the user
             // will see... if 0, typical "You must be logged in"
             // if 1, information that the user session was saved
-            // and will be resumed after (re)login
+            // and will be resumed after (re)login, if 2, there
+            // seems to have been a XSS or phishing attack (bad
+            // referrer)
             //
             $message = 0;
 
@@ -597,6 +609,13 @@ switch (PAGE_NAME) {
                 if ($session_expired_location == 'compose')
                     $message = 1;
             }
+
+            // was bad referrer the reason we were rejected?
+            //
+            if (sqsession_is_registered('user_is_logged_in')
+             && $check_referrer && !empty($referrer))
+                $message = 2;
+
             // signout page will deal with users who aren't logged
             // in on its own; don't show error here
             //
@@ -622,8 +641,10 @@ switch (PAGE_NAME) {
             set_up_language($squirrelmail_language, true);
             if (!$message)
                 logout_error( _("You must be logged in to access this page.") );
-            else
+            else if ($message == 1)
                 logout_error( _("Your session has expired, but will be resumed after logging in again.") );
+            else if ($message == 2)
+                logout_error( _("The current page request appears to have originated from an unrecognized source.") );
             exit;
         }