This is the tool for WordPress to manually deactivate any plugins and rollback to default theme.

wp-emergency.php

<?php
/**
 * WordPress Emergency Tools v1.0
 *
 * This is a tool to manually deactivate a theme and any plugins when you can not 
 * access the admin panel due to WordPress theme or plugins bug etc.
 * Usage it please place this file in the same directory as "wp-config.php" and 
 * access it directly from the browser.
 * Please delete this file promptly after use (If this file will remain, it will 
 * be a serious security hole for your service).
 *
 * Note: The author is not responsible for any trouble that occurred using this tool.
 *
 * @author: ka2
 *
 */

if ( ! defined( 'WP_DEFAULT_THEME' ) ) 
  define( 'WP_DEFAULT_THEME', 'twentyseventeen' );

session_start();

require_once( dirname(__FILE__) . '/wp-config.php' );

function dbConnect() {
  try {

    $_host = explode( ':', DB_HOST );
    $_dsn  = 'mysql:';
    $_dsn .= 'host=' . $_host[0] . ';';
    $_dsn .= ! empty( $_host[1] ) ? 'port=' . $_host[1] . ';' : '';
    $_dsn .= 'dbname=' . DB_NAME .';';
    $_dsn .= 'charset=' . DB_CHARSET;

    $db = new PDO( $_dsn, DB_USER, DB_PASSWORD, [
      PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
      PDO::ATTR_EMULATE_PREPARES => false
    ] );

    return $db;
  } catch ( PDOException $e ) {
    die( 'Database connection failed.' . $e->getMessage() );
  }
}

$db = dbConnect();

$result = '';
if ( ! empty( $_POST ) ) {
  $result .= deactivateComponents( $db, $table_prefix );
}
$result .= listComponents( $db, $table_prefix );

function listComponents( $db, $table_prefix ) {
  $components = array();
  // Get active plugins
  $sql = "SELECT option_value FROM {$table_prefix}options WHERE option_name = 'active_plugins'";
  $query = $db->query( $sql, PDO::FETCH_ASSOC );
  $res = $query->fetch();
  $components['plugins'] = unserialize( $res['option_value'] );
  // Get current theme
  $sql = "SELECT option_value FROM {$table_prefix}options WHERE option_name = 'current_theme'";
  $query = $db->query( $sql, PDO::FETCH_ASSOC );
  $res = $query->fetch();
  $components['theme'] = $res['option_value'];
  
  // Create list
  $doc  = '<form method="post" action="'. $_SERVER['PHP_SELF'] .'">';
  $doc .= '<ul style="list-style-type: none;">';
  $doc .= '<li><strong>Active Plugins</strong></li>';
  foreach ( $components['plugins'] as $_plugin ) {
    $doc .= '<li><label><input type="checkbox" name="plugins[]" value="'. $_plugin .'">'. substr( $_plugin, 0, strpos( $_plugin, '/' ) ) .'</label></li>';
  }
  $doc .= '<li><hr></li>';
  $doc .= '<li><strong>Current Theme</strong></li>';
  if ( ! empty( $components['theme'] ) ) {
    $doc .= '<li><label><input type="checkbox" name="theme" value="'. $components['theme'] .'">'. $components['theme'] .'</label></li>';
  } else {
    $doc .= '<li><span style="color:grey;margin-left:1em;">Undefiend</span></li>';
  }
  $doc .= '</ul>';
  $doc .= '<p>Submit after checked the components you want to deactivate.</p>';
  $doc .= '<input type="submit" value="Submit">';
  $doc .= '</form>';
  
  return $doc;
}

function deactivateComponents( $db, $table_prefix ) {
  $message = array();
  if ( array_key_exists( 'plugins', $_POST ) ) {
    $sql = "SELECT option_value FROM {$table_prefix}options WHERE option_name = 'active_plugins'";
    $query = $db->query( $sql, PDO::FETCH_ASSOC );
    $res = $query->fetch();
    $active_plugins = unserialize( $res['option_value'] );
    foreach ( $active_plugins as $_i => $_plugin ) {
      if ( in_array( $_plugin, $_POST['plugins'] ) ) {
        unset( $active_plugins[$_i] );
      }
    }
    $active_plugins = serialize( $active_plugins );
    $stmt = $db->prepare( "UPDATE {$table_prefix}options SET option_value = :value WHERE option_name = 'active_plugins'" );
    $stmt->bindParam( ':value', $active_plugins );
    if ( $stmt->execute() ) {
      $message[] = '<p style="color:green;">Deactivated the specified plugins.</p>';
    } else {
      $message[] = '<p style="color:red;">Could not deactivate the plugins.</p>';
    }
  }
  if ( array_key_exists( 'theme', $_POST ) ) {
    $default_theme = WP_DEFAULT_THEME;
    $stmt1 = $db->prepare( "UPDATE {$table_prefix}options SET option_value = :theme WHERE option_name = 'current_theme'" );
    $stmt1->bindParam( ':theme', $default_theme );
    $stmt2 = $db->prepare( "UPDATE {$table_prefix}options SET option_value = :theme WHERE option_name = 'template'" );
    $stmt2->bindParam( ':theme', $default_theme );
    $stmt3 = $db->prepare( "UPDATE {$table_prefix}options SET option_value = :theme WHERE option_name = 'stylesheet'" );
    $stmt3->bindParam( ':theme', $default_theme );
    if ( $stmt1->execute() && $stmt2->execute() && $stmt3->execute() ) {
      $message[] = '<p style="color:green;">Deactivated the current theme.</p>';
    } else {
      $message[] = '<p style="color:red;">Could not deactivate the current theme.</p>';
    }
  }
  
  session_destroy();
  return implode( "\n", $message );
}
?>
<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>WP Emergency Tool</title>
</head>
<body>
  <p>Now connecting to database of WordPress.</p>
  <?php echo $result; ?>
</body>
</html>