[aur-dev] [PATCH] validate email and fully check existence of it

[Lukas Fleischer]

On Tue, Mar 20, 2012 at 10:36:11AM +0100, BlackEagle wrote:
> - check if the format is valid
> - go and connect to the smtp server of the given domain and verify if
>   the given email exists there

I'm still not convinced that this is the right way to go. This check is
quite technical and looks error-prone, while it still allows anyone to
use arbitrary mail addresses (e.g. "archlinux at cryptocrack.de" or random
mail addresses from an email address list created by a crawler).

As I said on IRC, there's probably only two (proper) ways to fix this:

* Send verification mails.
* Use captchas.

I'll still add some comments to your patch below...

> ---
>  web/lib/aur.inc.php |   75 ++++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 files changed, 74 insertions(+), 1 deletions(-)
> 
> diff --git a/web/lib/aur.inc.php b/web/lib/aur.inc.php
> index c662b80..3fc0a14 100644
> --- a/web/lib/aur.inc.php
> +++ b/web/lib/aur.inc.php
> @@ -80,7 +80,80 @@ function check_sid($dbh=NULL) {
>  # verify that an email address looks like it is legitimate
>  #
>  function valid_email($addy) {
> -	return (filter_var($addy, FILTER_VALIDATE_EMAIL) !== false);
> +    // check against RFC 3696

Please use tabs, not spaces, for indentation.

> +    if(filter_var($addy, FILTER_VALIDATE_EMAIL) === false) {
> +        return false;
> +    }
> +
> +    // check dns for mx, a, aaaa records
> +    list($local, $domain) = explode('@', $addy);
> +    if(! (checkdnsrr($domain, 'MX') || checkdnsrr($domain, 'A') || checkdnsrr($domain, 'AAAA'))) {
> +        return false;
> +    }

This check could be dropped if we actually decided for this complicated
method. We check for MX records below.

> +
> +    // get mx records and check full email address
> +    $mxlist = array();
> +    $mxweight = array();
> +    getmxrr($domain, $mxlist, $mxweight);
> +    $mx = array_combine($mxweight, $mxlist);
> +    ksort($mx);

You checked for A and AAAA records above but don't add them to the "$mx"
array here?

> +
> +    //smtp_test_email($addy, current($mx));

Please strip commented code from patches.

> +    foreach($mx as $prio => $mxsrv) {
> +        if(smtp_test_email($addy, $mxsrv) === true) {
> +            return true;
> +        }
> +    }
> +
> +    return false;
> +}
> +
> +# verify that an email address exists on the smtp server
> +#
> +function smtp_test_email($addy, $mxsrv) {
> +    if(($smtp = fsockopen($mxsrv, 25)) === false) {
> +        return false;
> +    }
> +
> +    if(intval(preg_replace('/^\([0-9]{3}\).*/', '\1', fgets($smtp))) !== 220) {

Better use substr() here:

    if (intval(substr(fgets($smtp), 0, 3)) !== 220) {
    [...]

Also, what about other error codes, such as 421?

> +        smtp_close($smtp);
> +        return false;
> +    }
> +
> +    fwrite($smtp, "HELO $mxsrv\r\n");
> +    if(intval(preg_replace('/^\([0-9]{3}\).*/', '\1', fgets($smtp))) !== 250) {

Same here.

> +        smtp_close($smtp);
> +        return false;
> +    }
> +
> +    fwrite($smtp, "MAIL FROM: <mailtest at archlinux.org>\r\n");
> +    if(intval(preg_replace('/^\([0-9]{3}\).*/', '\1', fgets($smtp))) !== 250) {

Same here.

> +        smtp_close($smtp);
> +        return false;
> +    }
> +
> +    fwrite($smtp, "RCPT TO: <$addy>\r\n");
> +    $code = intval(preg_replace('/^\([0-9]{3}\).*/', '\1', fgets($smtp)));

Same here.

> +    /**
> +     * 250 = success
> +     * 451 or 452 = address got greylisted but another error occured
> +     *              so assume ok
> +     */
> +    if($code !== 250 && $code !== 451 && $code !== 452) {

What about 251? What about 450?

This is what I don't like about this patch... There's a dozens of corner
cases to consider and I don't think this is the right place to check for
these.

> +        smtp_close($smtp);
> +        return false;
> +    }
> +
> +    smtp_close($smtp);
> +    return true;
> +}
> +
> +# close smtp conneciton
> +#
> +function smtp_close(&$smtp) {
> +    fwrite($smtp, "RSET\r\n");
> +    fwrite($smtp, "QUIT\r\n");
> +    fclose($smtp);
>  }
>  
>  # a new seed value for mt_srand()
> -- 
> 1.7.9.1