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Message-ID: <20050702071037.GC23228@hardened-php.net> Date: Sat Jul 2 08:12:12 2005 From: sesser at hardened-php.net (Stefan Esser) Subject: Advisory 04/2005: Cacti Remote Command Execution Vulnerability -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hardened - PHP Project www.hardened-php.net -= Security Advisory =- Advisory: Cacti Remote Command Execution Vulnerability Release Date: 2005/07/01 Last Modified: 2005/07/01 Author: Stefan Esser [sesser@...dened-php.net] Application: Cacti <= 0.8.6e Severity: Wrongly implemented user input filters allows injection of user input into executed commandline Risk: Critical Vendor Status: Vendor has released an updated version References: http://www.hardened-php.net/advisory-042005.php Overview: Quote from http://www.cacti.net "Cacti is a complete network graphing solution designed to harness the power of RRDTool's data storage and graphing functionality. Cacti provides a fast poller, advanced graph templating, multiple data acquisition methods, and user management features out of the box. All of this is wrapped in an intuitive, easy to use interface that makes sense for LAN-sized installations up to complex networks with hundreds of devices." Alberto Trivero posted his Remote Command Execution Exploit for Cacti <= 0.8.6d to Bugtraq on the 22th June. Having analysed his bug we come to the conclusion, that the malfunctioning input filters, which were already mentioned in the previous advisory are also responsible for this bug still being exploitable. Details: With the recent release of Cacti 0.8.6e a number of user input filters were added to the codebase to prevent a number of SQL Injection problems. However these user input filters that made Alberto Trivero believe, that his remote command execution vulnerability was also fixed, are wrongly implemented and therefore can be bypassed to execute arbitrary commands on the webserver. To demonstrate the problem here a snipset of "graph_image.php" /* ================= input validation ================= */ input_validate_input_number(get_request_var("graph_start")); input_validate_input_number(get_request_var("graph_end")); input_validate_input_number(get_request_var("graph_height")); input_validate_input_number(get_request_var("graph_width")); input_validate_input_number(get_request_var("local_graph_id")); input_validate_input_number(get_request_var("rra_id")); /* ==================================================== */ ... /* override: graph start time (unix time) */ if (!empty($_GET["graph_start"])) { $graph_data_array["graph_start"] = $_GET["graph_start"]; } ... print rrdtool_function_graph($_GET["local_graph_id"], $_GET["rra_id"], $graph_data_array); On the first look this code looks like it has fixed the remote command execution vulnerability through the 'graph_*' request parameters, because it requires them to be a number before passing them to the rrdtool. To realize that this check is however worth nothing one has to dig deeper and look into the implementation of get_request_var() function get_request_var($name, $default = "") { if (isset($_REQUEST[$name])) { return $_REQUEST[$name]; } else { return $default; } } This actually means that the filter in this example is applied to the content of $_REQUEST["graph_start"] instead of $_GET["graph_start"]. The problem with this is, that $_REQUEST is a merged version of the $_GET, $_POST and $_COOKIE arrays and therefore array keys of the same name will overwrite each other in $_REQUEST. In the default configuration of PHP which is usually not changed by anyone the merge order is GPC. This means when the request contains both $_GET["graph_start"] and $_POST["graph_start"], only the posted value will end up in the $_REQUEST array. This however means, that an attacker can still inject shell commands by supplying the injection string through the URL and supplying a good string through POST or through the COOKIE. Proof of Concept: The Hardened-PHP Project is not going to release exploits for this vulnerabilities to the public. Disclosure Timeline: 25. June 2005 - Contacted Cacti developers via email 29. June 2005 - Review of patch from our side 1. July 2005 - Release of updated Cacti and Public Disclosure Recommendation: We strongly recommend upgrading to Cacti 0.8.6f which you can get at http://www.cacti.net/download_cacti.php Summary for Secunia: Because Secunia proofed several times in the past, that they have enormous problems with reading advisories and crediting the right parties in their advísory rip-offs, here a short summary. The bug described in this advisory is an input filtering malfunction. This is related to, but not exactly the bug Alberto Trivero found, because when he audited Cacti there was no input filtering at all. GPG-Key: http://www.hardened-php.net/hardened-php-signature-key.asc pub 1024D/0A864AA1 2004-04-17 Hardened-PHP Signature Key Key fingerprint = 066F A6D0 E57E 9936 9082 7E52 4439 14CC 0A86 4AA1 Copyright 2005 Stefan Esser. All rights reserved. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.6 (GNU/Linux) Comment: For info see http://www.gnupg.org iD8DBQFCxBcLRDkUzAqGSqERAgMuAKDkWDhBE2cpSfcaZ6K81IDmmZfqaACfcx6f 2ay9a8FMtLTkL0743yiMIrI= =C4+c -----END PGP SIGNATURE-----
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