From idlabs-advisories@idefense.com Tue Dec 21 04:28:28 2004 From: idlabs-advisories@idefense.com To: idlabs-advisories@idefense.com Date: Mon, 20 Dec 2004 17:51:24 -0500 Reply-To: customerservice@idefense.com Subject: [Full-Disclosure] iDEFENSE Security Advisory 12.20.04: IBM AIX chcod Local Privilege Escalation Vulnerability IBM AIX chcod Local Privilege Escalation Vulnerability iDEFENSE Security Advisory 12.20.04 www.idefense.com/application/poi/display?id=170&type=vulnerabilities December 20, 2004 I. BACKGROUND The chcod program is a setuid root application, installed by default under newer versions of IBM AIX, that manages capacity upgrade on demand (CUoD). II. DESCRIPTION Local exploitation of an untrusted path vulnerability in the chcod command included by default in multiple versions of IBM Corp. AIX could allow for arbitrary code execution as the root user. During execution, chcod invokes an external application ("grep") while trusting the user specified PATH environment variable. Root privileges are not dropped before this execution occurs, thus allowing an attacker to gain root access by specifying a controlled path and creating a malicious binary within that path. All an attacker needs to do to exploit the vulnerability is create a file called grep which contains malicious code, set their PATH variable to the current directory, and execute /usr/sbin/chcod. III. ANALYSIS The impact of this vulnerability is lessened by the fact that an attacker must first gain access to the "system" group in order to use this binary. Once group id "system" has been acquired, all that is required to exploit this vulnerability is a writable directory.  This directory can be the user's home directory, or even the /tmp directory, provided setuid execution is allowed. Exploitation does not require any knowledge of application internals, making privilege escalation trivial, even for unskilled attackers. IV. DETECTION iDEFENSE has confirmed the existence of this vulnerability in IBM AIX version 5.2. It is suspected that previous versions are also vulnerable.  V. WORKAROUND Only allow trusted users local access to security critical systems. Only allow trusted users access to the system group. Alternately, remove the setuid bit from chcod using chmod u-s /usr/sbin/chcod. VI. VENDOR RESPONSE "IBM provides the following fixes: APAR number for AIX 5.1.0: IY64356 (available) APAR number for AIX 5.2.0: IY64355 (available) APAR number for AIX 5.3.0: IY64354 (available) NOTE: Affected customers are urged to upgrade to 5.1.0, 5.2.0 or 5.3.0 at the latest maintenance level." VII. CVE INFORMATION The Common Vulnerabilities and Exposures (CVE) project has assigned the names CAN-2004-1028 to these issues. This is a candidate for inclusion in the CVE list (http://cve.mitre.org), which standardizes names for security problems. VIII. DISCLOSURE TIMELINE 11/02/2004       Initial vendor notification 11/04/2004       Initial vendor response 12/20/2004       Coordinated public disclosure IX. CREDIT iDEFENSE Labs is credited with this discovery. Get paid for vulnerability research http://www.idefense.com/poi/teams/vcp.jsp X. LEGAL NOTICES Copyright (c) 2004 iDEFENSE, Inc. Permission is granted for the redistribution of this alert electronically. It may not be edited in any way without the express written consent of iDEFENSE. If you wish to reprint the whole or any part of this alert in any other medium other than electronically, please email customerservice@idefense.com for permission. Disclaimer: The information in the advisory is believed to be accurate at the time of publishing based on currently available information. Use of the information constitutes acceptance for use in an AS IS condition. There are no warranties with regard to this information. Neither the author nor the publisher accepts any liability for any direct, indirect, or consequential loss or damage arising from use of, or reliance on, this information. _______________________________________________ Full-Disclosure - We believe in it. Charter: http://lists.netsys.com/full-disclosure-charter.html