From b5e0c16c04edcebdf5e81c39796a9d2c22cfd6f7 Mon Sep 17 00:00:00 2001
From: John Blackbourn <johnbillion@git.wordpress.org>
Date: Mon, 3 Mar 2025 09:49:36 +0000
Subject: [PATCH] Security: Reduce the length of the hash returned by
 `wp_fast_hash()` so it can be used in the `user_activation_key` field when a
 legacy database schema is still in use.

This reduces the hash length from 32 bytes to 30 so the overall length of an activation key after encoding, prefixing, and prepending a timestamp fits into 60 bytes.

A key is also introduced for domain separation. This doesn't affect the output length.

Props dd32, paragoninitiativeenterprises, peterwilsoncc, johnbillion

Fixes #21022

git-svn-id: https://develop.svn.wordpress.org/trunk@59904 602fd350-edb4-49c9-b593-d223f7449a82
---
 src/wp-includes/functions.php |  3 +-
 tests/phpunit/tests/auth.php  | 93 +++++++++++++++++++++++++++++++++++
 2 files changed, 95 insertions(+), 1 deletion(-)

diff --git a/src/wp-includes/functions.php b/src/wp-includes/functions.php
index 9a6938ed64..5696852f52 100644
--- a/src/wp-includes/functions.php
+++ b/src/wp-includes/functions.php
@@ -9142,7 +9142,8 @@ function wp_fast_hash(
 	#[\SensitiveParameter]
 	string $message
 ): string {
-	return '$generic$' . sodium_bin2hex( sodium_crypto_generichash( $message ) );
+	$hashed = sodium_crypto_generichash( $message, 'wp_fast_hash_6.8+', 30 );
+	return '$generic$' . sodium_bin2base64( $hashed, SODIUM_BASE64_VARIANT_URLSAFE_NO_PADDING );
 }
 
 /**
diff --git a/tests/phpunit/tests/auth.php b/tests/phpunit/tests/auth.php
index 6c22b89855..b8b6197a20 100644
--- a/tests/phpunit/tests/auth.php
+++ b/tests/phpunit/tests/auth.php
@@ -473,6 +473,99 @@ class Tests_Auth extends WP_UnitTestCase {
 		$this->assertSame( self::$user_id, $user->ID );
 	}
 
+	public function data_passwords(): array {
+		return array(
+			array( 'a' ),
+			array( 'password' ),
+			array( str_repeat( 'a', self::$password_length_limit ) ),
+		);
+	}
+
+	/**
+	 * Ensure the hash of the user password remains less than 64 characters in length to account for the old users table schema.
+	 *
+	 * @ticket 21022
+	 * @dataProvider data_passwords
+	 */
+	public function test_user_password_against_old_users_table_schema( string $password ) {
+		// Mimic the schema of the users table prior to WordPress 4.4.
+		add_filter( 'wp_pre_insert_user_data', array( $this, 'mimic_users_schema_prior_to_44' ) );
+
+		$username = 'old-schema-user';
+
+		// Create a user.
+		$user_id = $this->factory()->user->create(
+			array(
+				'user_login' => $username,
+				'user_email' => 'old-schema-user@example.com',
+				'user_pass'  => $password,
+			)
+		);
+
+		// Check the user can authenticate.
+		$user = wp_authenticate( $username, $password );
+
+		$this->assertNotWPError( $user );
+		$this->assertInstanceOf( 'WP_User', $user );
+		$this->assertSame( $user_id, $user->ID, 'User should be able to authenticate' );
+		$this->assertNotSame( self::$user_id, $user->ID, 'A unique user must be created for this test, the shared fixture must not be used' );
+	}
+
+	/**
+	 * Ensure the hash of the user activation key remains less than 60 characters in length to account for the old users table schema.
+	 *
+	 * @ticket 21022
+	 */
+	public function test_user_activation_key_against_old_users_table_schema() {
+		// Mimic the schema of the users table prior to WordPress 4.4.
+		add_filter( 'wp_pre_insert_user_data', array( $this, 'mimic_users_schema_prior_to_44' ) );
+
+		$username = 'old-schema-user';
+
+		// Create a user.
+		$user_id = $this->factory()->user->create(
+			array(
+				'user_login' => $username,
+				'user_email' => 'old-schema-user@example.com',
+			)
+		);
+
+		$user = get_userdata( $user_id );
+		$key  = get_password_reset_key( $user );
+
+		// A correctly saved key should be accepted.
+		$check = check_password_reset_key( $key, $user->user_login );
+
+		$this->assertNotWPError( $check );
+		$this->assertInstanceOf( 'WP_User', $check );
+		$this->assertSame( $user->ID, $check->ID );
+		$this->assertNotSame( self::$user_id, $user->ID, 'A unique user must be created for this test, the shared fixture must not be used' );
+	}
+
+	/*
+	 * Fake the schema of the users table prior to WordPress 4.4 to mimic sites that are using the
+	 * `DO_NOT_UPGRADE_GLOBAL_TABLES` constant and have not updated the users table schema.
+	 *
+	 * The schema of the wp_users table on wordpress.org has not been updated since the schema was changed in [35638]
+	 * for WordPress 4.4, which means the `user_activation_key` field remains at 60 characters length and the `user_pass`
+	 * field remains at 64 characters length instead of the expected 255. Although this is unlikely to affect other
+	 * sites, this can be accommodated for in the codebase.
+	 *
+	 * Actually altering the database schema during tests will commit the transaction and break subsequent tests, hence
+	 * the use of this filter.
+	 */
+	public function mimic_users_schema_prior_to_44( array $data ): array {
+		if ( isset( $data['user_pass'] ) ) {
+			$this->assertLessThanOrEqual( 64, strlen( $data['user_pass'] ) );
+		}
+
+		if ( isset( $data['user_activation_key'] ) ) {
+			$this->assertLessThanOrEqual( 60, strlen( $data['user_activation_key'] ) );
+		}
+
+		return $data;
+	}
+
 	/**
 	 * @ticket 21022
 	 */