diff --git a/wp-includes/functions.php b/wp-includes/functions.php
index c303f0d4a6..563c4d78b8 100644
--- a/wp-includes/functions.php
+++ b/wp-includes/functions.php
@@ -2079,7 +2079,6 @@ function wp_mkdir_p( $target ) {
  * For example, '/foo/bar', or 'c:\windows'.
  *
  * @since 2.5.0
- * @since 6.1.0 Allows normalized Windows paths (forward slashes).
  *
  * @param string $path File path.
  * @return bool True if path is absolute, false is not absolute.
@@ -2110,11 +2109,6 @@ function path_is_absolute( $path ) {
 		return true;
 	}
 
-	// Normalized Windows paths for local filesystem and network shares (forward slashes).
-	if ( preg_match( '#(^[a-zA-Z]+:/|^//[\w!@\#\$%\^\(\)\-\'{}\.~]{1,15})#', $path ) ) {
-		return true;
-	}
-
 	// A path starting with / or \ is absolute; anything else is relative.
 	return ( '/' === $path[0] || '\\' === $path[0] );
 }
diff --git a/wp-includes/post.php b/wp-includes/post.php
index a67d7a79a1..d7e7bfec99 100644
--- a/wp-includes/post.php
+++ b/wp-includes/post.php
@@ -724,11 +724,10 @@ function get_attached_file( $attachment_id, $unfiltered = false ) {
 	$file = get_post_meta( $attachment_id, '_wp_attached_file', true );
 
 	// If the file is relative, prepend upload dir.
-	if ( $file ) {
+	if ( $file && 0 !== strpos( $file, '/' ) && ! preg_match( '|^.:\\\|', $file ) ) {
 		$uploads = wp_get_upload_dir();
-
 		if ( false === $uploads['error'] ) {
-			$file = path_join( $uploads['basedir'], $file );
+			$file = $uploads['basedir'] . "/$file";
 		}
 	}
 
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 54acffcf04..076c45a28d 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.1-RC4-54709';
+$wp_version = '6.1-RC4-54713';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.