From 80f1bf0fe40714165a40b4afafaaeaa0b56d6a47 Mon Sep 17 00:00:00 2001
From: Bishal Shrestha <57122064+bishalsthadev@users.noreply.github.com>
Date: Sun, 20 Sep 2026 09:49:56 +0545
Subject: [PATCH] Plugins: Fix wp_edit_theme_plugin_file() to detect
 network-active plugins.

$is_active only checked the site-level active_plugins option, so the
fatal-error loopback check was silently skipped for network-active
plugins. Use is_plugin_active() instead, which already accounts for
network activation.
---
 src/wp-admin/includes/file.php             |  6 +--
 tests/phpunit/tests/admin/includesFile.php | 45 ++++++++++++++++++++++
 2 files changed, 46 insertions(+), 5 deletions(-)

diff --git a/src/wp-admin/includes/file.php b/src/wp-admin/includes/file.php
index ef5a5025bef22..79a08bb2b9cba 100644
--- a/src/wp-admin/includes/file.php
+++ b/src/wp-admin/includes/file.php
@@ -425,11 +425,7 @@ function wp_edit_theme_plugin_file( $args ) {
 
 		$real_file = WP_PLUGIN_DIR . '/' . $file;
 
-		$is_active = in_array(
-			$plugin,
-			(array) get_option( 'active_plugins', array() ),
-			true
-		);
+		$is_active = is_plugin_active( $plugin );
 
 	} elseif ( ! empty( $args['theme'] ) ) {
 		$stylesheet = $args['theme'];
diff --git a/tests/phpunit/tests/admin/includesFile.php b/tests/phpunit/tests/admin/includesFile.php
index fab002c5e5e2c..62e0e0ef4038d 100644
--- a/tests/phpunit/tests/admin/includesFile.php
+++ b/tests/phpunit/tests/admin/includesFile.php
@@ -463,4 +463,49 @@ function () {
 			'.tmp',
 		);
 	}
+
+	/**
+	 * @ticket 66129
+	 * @group multisite
+	 * @group ms-required
+	 */
+	public function test_wp_edit_theme_plugin_file_runs_loopback_check_for_network_active_plugin() {
+		$user_id = self::factory()->user->create();
+		grant_super_admin( $user_id );
+		wp_set_current_user( $user_id );
+
+		$plugin = 'hello.php';
+		activate_plugin( $plugin, '', true );
+
+		$loopback_requested = false;
+		add_filter(
+			'pre_http_request',
+			function ( $preempt, $parsed_args, $url ) use ( &$loopback_requested ) {
+				if ( str_contains( $url, 'wp_scrape_key' ) ) {
+					$loopback_requested = true;
+					return array(
+						'body'     => '',
+						'response' => array( 'code' => 200 ),
+					);
+				}
+				return $preempt;
+			},
+			10,
+			3
+		);
+
+		wp_edit_theme_plugin_file(
+			array(
+				'plugin'     => $plugin,
+				'file'       => $plugin,
+				'newcontent' => file_get_contents( WP_PLUGIN_DIR . '/' . $plugin ),
+				'nonce'      => wp_create_nonce( 'edit-plugin_' . $plugin ),
+			)
+		);
+
+		deactivate_plugins( $plugin );
+		revoke_super_admin( $user_id );
+
+		$this->assertTrue( $loopback_requested, 'Editing a network-active plugin file should trigger the fatal-error loopback check.' );
+	}
 }