Index: wp-content/themes/twentyeleven/content-single.php
===================================================================
--- wp-content/themes/twentyeleven/content-single.php	(revision 20500)
+++ wp-content/themes/twentyeleven/content-single.php	(working copy)
@@ -57,7 +57,7 @@
 				<?php echo get_avatar( get_the_author_meta( 'user_email' ), apply_filters( 'twentyeleven_author_bio_avatar_size', 68 ) ); ?>
 			</div><!-- #author-avatar -->
 			<div id="author-description">
-				<h2><?php printf( __( 'About %s', 'twentyeleven' ), get_the_author() ); ?></h2>
+				<h2><?php echo esc_html( sprintf( __( 'About %s', 'twentyeleven' ), get_the_author() ) ); ?></h2>
 				<?php the_author_meta( 'description' ); ?>
 				<div id="author-link">
 					<a href="<?php echo esc_url( get_author_posts_url( get_the_author_meta( 'ID' ) ) ); ?>" rel="author">