Re: PHPCentral Login Script Remote Command Execution Vulnerability

Magnus Holmgren said:

>[the superglobals] shadow everything - you cannot define your own
>$_SERVER array, nor can it be overridden with HTTP GET or POST
>values. If that were possible, using the superglobals would be
>useless; all scripts would be vulnerable unless register_globals is
>off.

This EXACT problem occurred in older versions of PHP, at least 4.x if I recall correctly, although I can't dig up which versions were affected. Now, you could argue that this is the PHP interpreter's fault, so the applications shouldn't be held accountable, but we see a lot of reports like this one - and I bet they work in many environments. Then there's the unset() vulnerability [1] and other variants.

Ignoring register_globals, there's still dynamic variable evaluation [2], extract(), and other variable-overwriting constructs, from which I suspect even the superglobals aren't always protected, although these constructs don't seem to be used very heavily.

>Now, register_globals has defaulted to off ever since PHP 4.2.0.

This is a reasonable argument. However, many hosting sites and applications still enable or require it. The mass compromises of web servers for botnets, as described by Gadi Evron [3], were probably made possible due to this setting (and allow_url_fopen).

>And it would of course be nice if people posting to Bugtraq actually
>tested their PoCs first.

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This would be nice, but as you see, sometimes a "fake" isn't always so immediately identified, thanks to the colorful, complicated history of the PHP interpreter itself [4] [5] [6].

• Steve

[1] Zend_Hash_Del_Key_Or_Index Vulnerability

   CVE-2006-3017
   Stefan Esser
  http://www.hardened-php.net/hphp/zend_hash_del_key_or_index_vulnerability.html

[2] Dynamic Evaluation Vulnerabilities in PHP applications

    http://www.securityfocus.com/archive/1/432828

[3] "Web server botnets and hosting farms as attack platforms"

    Gadi Evron, Kfir Damari & Noam Rathaus, Virus Bulletin, February 2007

[4] $GLOBALS Overwrite and it's Consequences

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    Stefan Esser
    http://www.hardened-php.net/globals-problem

[5] PHP import_request_variables() arbitrary variable overwrite

    Stefano Di Paola
    http://www.securityfocus.com/archive/1/archive/1/462263/100/0/threaded

[6] http://www.hardened-php.net/advisories.15.html Received on Wed Aug 15 12:03:09 2007