Merge pull request #33 from kristianwind/shared-menu-1-2-0

Take shared-menu.php 1.2.0: the glyph is CSS-escaped, not esc_attr'd

ci/plugin.conf

@@ -75,6 +75,12 @@ RELEASE_REPO=kw/nolimit-discounts-dist
 # The frozen hash is therefore a family-wide fact, not a local one, and taking
 # a new one is something all six do in the same window.
 #
-# 184cebdc = contract 1.1.0 (the ∞ glyph, and the header/count corrections
+# 9012fe98 = contract 1.2.0. The glyph is now emitted as CSS numeric escapes
-# Nolimit SEO found). Previous frozen hash was f4862d5c = 1.0.0.
+# rather than through esc_attr(): HTML entities are not decoded by the CSS
-WPMGR_MENU_SHA=184cebdcd86024d4e864c529bc68ead0f7d63656d9bb3dfe0e1fdf3203e364ae
+# parser, so esc_attr was protecting by coincidence — and a backslash, which it
+# leaves alone, IS a CSS escape and swallowed the closing quote. Changing the
+# alphabet beats filtering the input: what is emitted is nothing but
+# backslashes, hex digits and spaces, so there is nothing left to leave the
+# string with. Verified here against seven hostile inputs.
+# Earlier frozen hashes: 184cebdc = 1.1.0, f4862d5c = 1.0.0.
+WPMGR_MENU_SHA=9012fe98d867b86c993cee2f8d7b0b9fe5b89817fed4cf45346aa4949e2df307

includes/shared-menu.php

@@ -69,7 +69,7 @@ if ( ! defined( 'ABSPATH' ) ) {
 }
 
 if ( ! defined( 'WPMGR_MENU_VERSION' ) ) {
-	define( 'WPMGR_MENU_VERSION', '1.1.0' );
+	define( 'WPMGR_MENU_VERSION', '1.2.0' );
 }
 
 if ( ! defined( 'WPMGR_MENU_SLUG' ) ) {
@@ -168,11 +168,84 @@ if ( ! function_exists( 'wpmgr_ensure_menu' ) ) {
 			return;
 		}
 
+		// phpcs:disable WordPress.Security.EscapeOutput.OutputNotEscaped -- the slug is reduced to [a-z0-9_-] and the glyph to CSS numeric escapes; both are escaped for the context they are printed in, which is CSS rather than HTML.
 		printf(
 			'<style>#adminmenu .toplevel_page_%1$s .wp-menu-image::before{content:"%2$s";font-family:-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,sans-serif;font-size:20px;font-weight:400;line-height:1.4}</style>',
-			esc_attr( WPMGR_MENU_SLUG ),
+			preg_replace( '/[^a-z0-9_-]/', '', strtolower( WPMGR_MENU_SLUG ) ),
-			esc_attr( $glyph )
+			wpmgr_css_escape( $glyph )
 		);
+		// phpcs:enable WordPress.Security.EscapeOutput.OutputNotEscaped
+	}
+
+	/**
+	 * A string that is safe inside a CSS string literal, whatever it was.
+	 *
+	 * 🔴 esc_attr() is the wrong tool here and it protected by accident.
+	 * Nolimit Discounts measured it: a glyph of `x"} body{display:none}` comes
+	 * out as `x&quot;} …`, the CSS string never closes, and nothing breaks
+	 * out — but only because the entity happens to contain no quote. The CSS
+	 * parser does not decode HTML entities, so it was never escaping in this
+	 * context; it was a substitution that coincidentally removed the one
+	 * character that mattered. Two things follow from that: a glyph containing
+	 * a quote renders as the literal text `&quot;` in the menu, and a single
+	 * backslash — which esc_attr() leaves alone, and which IS an escape to the
+	 * CSS parser — swallows the closing quote and the rest of the rule with
+	 * it. Measured, not reasoned: the string then runs on to the quote in
+	 * "Segoe UI" and the declaration block is corrupt.
+	 *
+	 * So do not filter the input; change its alphabet. Every character becomes
+	 * a CSS numeric escape, so the emitted value contains nothing but
+	 * backslashes, hex digits and spaces and cannot leave the string for any
+	 * input at all. No whitelist to keep honest, no character class to get
+	 * wrong, and an emoji still works.
+	 *
+	 * The decoder is written out rather than using mb_ord() because WordPress
+	 * supports installs without mbstring, and ord() on a multi-byte character
+	 * silently yields the first byte — which would render our own ∞ as
+	 * mojibake on exactly those installs and on no machine any of us test on.
+	 *
+	 * @param string $text Text from a filter, i.e. arbitrary.
+	 * @return string CSS escapes, safe between double quotes.
+	 */
+	function wpmgr_css_escape( $text ) {
+		$out = '';
+		$len = strlen( $text );
+
+		for ( $i = 0; $i < $len; $i++ ) {
+			$byte = ord( $text[ $i ] );
+
+			if ( $byte < 0x80 ) {
+				$code = $byte;
+				$tail = 0;
+			} elseif ( $byte >= 0xF0 ) {
+				$code = $byte & 0x07;
+				$tail = 3;
+			} elseif ( $byte >= 0xE0 ) {
+				$code = $byte & 0x0F;
+				$tail = 2;
+			} elseif ( $byte >= 0xC0 ) {
+				$code = $byte & 0x1F;
+				$tail = 1;
+			} else {
+				continue;   // A stray continuation byte is not a character.
+			}
+
+			while ( $tail > 0 && $i + 1 < $len && 0x80 === ( ord( $text[ $i + 1 ] ) & 0xC0 ) ) {
+				++$i;
+				$code = ( $code << 6 ) | ( ord( $text[ $i ] ) & 0x3F );
+				--$tail;
+			}
+
+			if ( $tail > 0 ) {
+				continue;   // Truncated sequence.
+			}
+
+			// The trailing space terminates the escape, so a following hex
+			// digit cannot be read as part of it.
+			$out .= sprintf( '\\%X ', $code );
+		}
+
+		return $out;
 	}
 
 	/**