Fix (again) bug where image data URIs in css style were treated as evil/remote in mail preview (#5580)

CHANGELOG

@@ -9,6 +9,7 @@ CHANGELOG Roundcube Webmail
 - Fix wording of "Mark previewed messages as read" to "Mark messages as read" (#5952)
 - Enigma: Fix decryption of messages encoded with non-ascii charset (#5962)
 - Fix missing cursor in HTML editor on mail reply (#5969)
+- Fix (again) bug where image data URIs in css style were treated as evil/remote in mail preview (#5580)
 
 RELEASE 1.3.1
 -------------

program/lib/Roundcube/rcube_utils.php

@@ -407,10 +407,17 @@ class rcube_utils
             if ($allow_remote) {
                 $a_styles = preg_split('/;[\r\n]*/', $styles, -1, PREG_SPLIT_NO_EMPTY);
 
-                foreach ($a_styles as $line) {
+                for ($i=0, $len=count($a_styles); $i < $len; $i++) {
+                    $line     = $a_styles[$i];
                     $stripped = preg_replace('/[^a-z\(:;]/i', '', $line);
-                    // ... and only allow strict url() values
-                    if (stripos($stripped, 'url(') && !preg_match($strict_url_regexp, $line)) {
+
+                    // allow data:image uri, join with continuation
+                    if (stripos($stripped, 'url(data:image')) {
+                        $a_styles[$i] .= ';' . $a_styles[$i+1];
+                        unset($a_styles[$i+1]);
+                    }
+                    // allow strict url() values only
+                    else if (stripos($stripped, 'url(') && !preg_match($strict_url_regexp, $line)) {
                         $a_styles = array('/* evil! */');
                         break;
                     }

tests/Framework/Utils.php

@@ -218,7 +218,9 @@ class Framework_Utils extends PHPUnit_Framework_TestCase
 
         // allow data URIs with images (#5580)
         $mod = rcube_utils::mod_css_styles("body { background-image: url(data:image/png;base64,123); }", 'rcmbody');
-        $this->assertEquals("#rcmbody { background-image: url(data:image/png;base64,123); }", $mod, "Data URIs in url() allowed");
+        $this->assertContains("#rcmbody { background-image: url(data:image/png;base64,123);", $mod, "Data URIs in url() allowed [1]");
+        $mod = rcube_utils::mod_css_styles("body { background-image: url(data:image/png;base64,123); }", 'rcmbody', true);
+        $this->assertContains("#rcmbody { background-image: url(data:image/png;base64,123);", $mod, "Data URIs in url() allowed [2]");
     }
 
     function test_xss_entity_decode()