HTML API: Improve script tag escape state processing.

Addresses some edge cases parsing of script tag contents:

- "<!-->" remains in the unescaped state and does not enter the escaped state.
- Contents in the escaped state that end with "<script" do not enter double-escaped state.
- "\f" (Form Feed) was missing as a tag name terminating character.

Developed in WordPress/wordpress-develop#9397 and WordPress/wordpress-develop#9402.

Props jonsurrell, dmsnell.
See #63738.

Built from https://develop.svn.wordpress.org/trunk@60649


git-svn-id: https://core.svn.wordpress.org/trunk@59985 1a063a9b-81f0-0310-95a4-ce76da25c4cd

Author: sirreal

wp-includes/html-api/class-wp-html-tag-processor.php

@@ -1556,24 +1556,33 @@ private function skip_script_data(): bool {
 			}
 
 			/*
-			 * Unlike with "-->", the "<!--" only transitions
-			 * into the escaped mode if not already there.
-			 *
-			 * Inside the escaped modes it will be ignored; and
-			 * should never break out of the double-escaped
-			 * mode and back into the escaped mode.
-			 *
-			 * While this requires a mode change, it does not
-			 * impact the parsing otherwise, so continue
-			 * parsing after updating the state.
+			 * "<!--" only transitions from _unescaped_ to _escaped_. This byte sequence is only
+			 * significant in the _unescaped_ state and is ignored in any other state.
 			 */
 			if (
+				'unescaped' === $state &&
 				'!' === $html[ $at ] &&
 				'-' === $html[ $at + 1 ] &&
 				'-' === $html[ $at + 2 ]
 			) {
-				$at   += 3;
-				$state = 'unescaped' === $state ? 'escaped' : $state;
+				$at += 3;
+
+				/*
+				 * The parser is ready to enter the _escaped_ state, but may remain in the
+				 * _unescaped_ state. This occurs when "<!--" is immediately followed by a
+				 * sequence of 0 or more "-" followed by ">". This is similar to abruptly closed
+				 * HTML comments like "<!-->" or "<!--->".
+				 *
+				 * Note that this check may advance the position significantly and requires a
+				 * length check to prevent bad offsets on inputs like `<script><!---------`.
+				 */
+				$at += strspn( $html, '-', $at );
+				if ( $at < $doc_length && '>' === $html[ $at ] ) {
+					++$at;
+					continue;
+				}
+
+				$state = 'escaped';
 				continue;
 			}
 
@@ -1610,8 +1619,30 @@ private function skip_script_data(): bool {
 			 */
 			$at += 6;
 			$c   = $html[ $at ];
-			if ( ' ' !== $c && "\t" !== $c && "\r" !== $c && "\n" !== $c && '/' !== $c && '>' !== $c ) {
-				++$at;
+			if (
+				/**
+				 * These characters trigger state transitions of interest:
+				 *
+				 * - @see {https://html.spec.whatwg.org/multipage/parsing.html#script-data-end-tag-name-state}
+				 * - @see {https://html.spec.whatwg.org/multipage/parsing.html#script-data-escaped-end-tag-name-state}
+				 * - @see {https://html.spec.whatwg.org/multipage/parsing.html#script-data-double-escape-start-state}
+				 * - @see {https://html.spec.whatwg.org/multipage/parsing.html#script-data-double-escape-end-state}
+				 *
+				 * The "\r" character is not present in the above references. However, "\r" must be
+				 * treated the same as "\n". This is because the HTML Standard requires newline
+				 * normalization during preprocessing which applies this replacement.
+				 *
+				 * - @see https://html.spec.whatwg.org/multipage/parsing.html#preprocessing-the-input-stream
+				 * - @see https://infra.spec.whatwg.org/#normalize-newlines
+				 */
+				'>' !== $c &&
+				' ' !== $c &&
+				"\n" !== $c &&
+				'/' !== $c &&
+				"\t" !== $c &&
+				"\f" !== $c &&
+				"\r" !== $c
+			) {
 				continue;
 			}
 

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.9-alpha-60648';
+$wp_version = '6.9-alpha-60649';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.