Source

File: wp-includes/pluggable.php

function wp_generate_password( $length = 12, $special_chars = true, $extra_special_chars = false ) {
		$chars = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
		if ( $special_chars ) {
			$chars .= '!@#$%^&*()';
		}
		if ( $extra_special_chars ) {
			$chars .= '-_ []{}<>~`+=,.;:/?|';
		}

		$password = '';
		for ( $i = 0; $i < $length; $i++ ) {
			$password .= substr( $chars, wp_rand( 0, strlen( $chars ) - 1 ), 1 );
		}

		/**
		 * Filters the randomly-generated password.
		 *
		 * @since 3.0.0
		 * @since 5.3.0 Added the `$length`, `$special_chars`, and `$extra_special_chars` parameters.
		 *
		 * @param string $password            The generated password.
		 * @param int    $length              The length of password to generate.
		 * @param bool   $special_chars       Whether to include standard special characters.
		 * @param bool   $extra_special_chars Whether to include other special characters.
		 */
		return apply_filters( 'random_password', $password, $length, $special_chars, $extra_special_chars );
	}