我可以通过更换CR来避免CRLF注入攻击吗？

Question

我有一个允许一个文件附件的表单,并生成一个硬编码地址的电子邮件.我想避免恶意用户输入自定义邮件头的可能性(CRLF注入,因为电子邮件头根据RFC以\ r \n结尾,因此被调用).

假设我对每个可能进入$ additional_headers参数的数据运行以下函数:

<?php

function strip_crlf($string){ return str_replace("\r\n", "\n", $string); }

?>

这取代了CRLF对的回车一半.这会充分防止潜在的攻击吗？

通常我会用空字符串替换\ r \n.但是这种特殊形式允许一个附件,这意味着消息体实际上最终通过$ additional_headers参数传递,因为PHP没有用于构建多部分MIME编码电子邮件的本机函数(我知道).

如果有人关心,这是我邮寄附件的功能:

<?php
function mail_attachment($to, $from, $from_name, $subject, $message, $file = false, $filename = false, $filetype = false){

    // Remove CRLF sequences from everything that might go into a header
    $from = strip_crlf($from);
    $from_name = strip_crlf($from_name);
    $message = strip_crlf($message);
    if($filename){ $filename = strip_crlf($filename); }
    if($filetype){ $filetype = strip_crlf($filetype); }

    // $to and $subject escaping handled natively by mail();
    // $file is base64 encoded before mail_attachment() is called.

    $header = '';

    // No file attachment; just send a regular email.
    if(!$file){
        $header .= "From: ".$from_name." <".$from.">\r\n";
        return mail($to, $subject, $message, $header);
    }

    $uid = md5(uniqid(time()));

    // Build a MIME encoded message.
    $header .= "MIME-Version: 1.0\r\n";
    $header .= "Content-Type: multipart/mixed; boundary=\"$uid\"\r\n\r\n";
    $header .= "This is a multi-part message in MIME format.\r\n";
    $header .= "--$uid\r\n";
    $header .= "Content-type:text/plain; charset=utf-8\r\n";
    $header .= "Content-Transfer-Encoding: 8bit\r\n\r\n";
    $header .= "$message\r\n\r\n";
    $header .= "--$uid\r\n";
    $header .= "Content-Type: $filetype; name=\"$filename\"\r\n";
    $header .= "Content-Transfer-Encoding: base64\r\n";
    $header .= "Content-Disposition: attachment; filename=\"$filename\"\r\n\r\n";
    $header .= "$file\r\n\r\n";
    $header .= "--$uid--";

    // Send the mail.
    return mail($to, $subject, '', $header);
}

?>

Answer 1

如果您担心注射,那么不要建立自己的消息.使用Swiftmailer或PHPMailer,它可以帮助您解决所有这些问题.