From a788a6188fc93bd49f9b23125783ec22b8bd7c7c Mon Sep 17 00:00:00 2001
From: Brian Wolff <bawolff+wn@gmail.com>
Date: Sun, 24 Sep 2017 00:57:05 +0000
Subject: [PATCH] SECURITY: Ensure Message::rawParams can't lead to XSS

If you used wfMessage( 'foo' )->rawParams( 'bar"baz' )
there's a possibility of leading to xss, if the foo
message has a $1 in an attribute, as the quote characters
may end the attribute.

To prevent that, we convert $1 to $'"1 for after parameters,
so if any of them end up in attributes, the attribute escaping
will break the parameter name, preventing substitution.

This would of course break if someone intentionally inserted
a raw parameter into an attribute, but that's silly and I
don't think we should allow that.

This is similar to the parser strip marker issue.

Bug: T176247
Change-Id: If83aec01b20e414f9c92be894f145d7df2974866
---
 includes/Message.php | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/includes/Message.php b/includes/Message.php
index fd67613e28..42351afe4d 100644
--- a/includes/Message.php
+++ b/includes/Message.php
@@ -1123,11 +1123,29 @@ class Message implements MessageSpecifier, Serializable {
 	 * @return string
 	 */
 	protected function replaceParameters( $message, $type = 'before', $format ) {
+		// A temporary marker for $1 parameters that is only valid
+		// in non-attribute contexts. However if the entire message is escaped
+		// then we don't want to use it because it will be mangled in all contexts
+		// and its unnessary as ->escaped() messages aren't html.
+		$marker = $format === self::FORMAT_ESCAPED ? '$' : '$\'"';
 		$replacementKeys = [];
 		foreach ( $this->parameters as $n => $param ) {
 			list( $paramType, $value ) = $this->extractParam( $param, $format );
-			if ( $type === $paramType ) {
-				$replacementKeys['$' . ( $n + 1 )] = $value;
+			if ( $type === 'before' ) {
+				if ( $paramType === 'before' ) {
+					$replacementKeys['$' . ( $n + 1 )] = $value;
+				} else /* $paramType === 'after' */ {
+					// To protect against XSS from replacing parameters
+					// inside html attributes, we convert $1 to $'"1.
+					// In the event that one of the parameters ends up
+					// in an attribute, either the ' or the " will be
+					// escaped, breaking the replacement and avoiding XSS.
+					$replacementKeys['$' . ( $n + 1 )] = $marker . ( $n + 1 );
+				}
+			} else {
+				if ( $paramType === 'after' ) {
+					$replacementKeys[$marker . ( $n + 1 )] = $value;
+				}
 			}
 		}
 		$message = strtr( $message, $replacementKeys );
-- 
2.14.1