Bug #68081 [Com]: checkdnsrr( 'example.com' ) returns `true` when no MX, only CNAME

Edit report at https://bugs.php.net/bug.php?id=68081&edit=1 ID: 68081 Comment by: kriscraig@php.net Reported by: figureonecpr at gmail dot com Summary: checkdnsrr( 'example.com' ) returns true when no MX, only CNAME Status: Assigned Type: Bug Package: Network related Operating System: Linux Phoenix 2.6.32 PHP Version: master-Git-2014-09-23 (snap) Assigned To: kriscraig Block user comment: N Private report: N New Comment: Could you include the actual hostname you used? That'll make it easier for me to repro. Thanks! --Kris Previous Comments: ------------------------------------------------------------------------ [2014-09-23 03:52:26] figureonecpr at gmail dot com Description: ------------ Per http://php.net/manual/en/function.checkdnsrr.php, checkdnsrr() defaults to an MX record query when the second argument is not supplied. Regardless of SMTP's implicit MX logic, this function is supposed to return false if $host does not have at least one *explicit* MX in the DNS. However, if the supplied hostname simply has a CNAME record (a good CNAME, one that can be dereferenced to an extant canonical hostname) the function returns true. The bug is seen regardless of whether the canonical hostname itself has an MX record. For example, if you have somehost.example.com CNAME --> example.com A and do checkdnsrr( 'somehost.example.com' ) you will get true. But if you go straight to the canonical A record and do checkdnsrr( 'example.com' ) you will get false. Test script: --------------- // where cname.example.com exists is a CNAME in the DNS pointing to an extant canonical hostname var_dump( checkdnsrr( 'cname.example.com' ) ); Expected result: ---------------- boolean(false) Actual result: -------------- boolean(true) ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=68081&edit=1