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

[Slavi Pantaleev]

Contacting the mail server to verify that the mailbox exists seems a little
excessive.
I think just checking for an MX/A record is good in catching some obviously
fake addresses and reliable enough.
Maybe we should just stop there.

On Tue, Mar 20, 2012 at 12:31 PM, Lukas Fleischer
<archlinux at cryptocrack.de>wrote:

> 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
>