SCO Openserver authsh 'Home' Buffer Overflow Vulnerability

iDEFENSE Security Advisory 10.24.05
http://www.idefense.com/application/poi/display?type=vulnerabilities
October 24, 2005

I. BACKGROUND

SCO OpenServer is a UNIX-like operating system for x86 platforms.

II. DESCRIPTION

Local exploitation of a buffer overflow vulnerability in The SCO Group 
Inc.'s Openserver operating system could allow an attacker to gain root 
privileges.

The authsh utility is a standard binary distributed with the Openserver 
platform. The vulnerability specifically exists because of a lack of 
bounds checking on the value given to the "HOME" environment variable. 
Local attackers can supply a specially crafted string to overflow a 
stack buffer and execute arbitrary code with group auth privileges.

III. ANALYSIS

Successful exploitation of this vulnerability will result in execution 
of arbitrary code with permissions of the running process. The binary is

setgid auth by default and can be used by attackers with a local account

to gain root privileges, as the group auth has write access to system 
authentication information. An attacker would only need to modify the 
system passwd file to grant an account they control superuser 
privileges.

IV. DETECTION

iDEFENSE has confirmed the existence of this vulnerability in SCO 
Openserver 5.0.7. It is suspected that earlier versions are also 
vulnerable.

V. WORKAROUND

As a workaround solution, remove the setgid bit from the authsh binary 
until a vendor patch can be applied. 

  # chmod -g /opt/K/SCO/Unix/5.0.7Hw/usr/lib/sysadm/authsh

VI. VENDOR RESPONSE

The vendor has released the following advisory for this issue:

ftp://ftp.sco.com/pub/updates/OpenServer/SCOSA-2005.40/SCOSA-2005.40.txt

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2005-2926 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org), which standardizes names for
security problems.

VIII. DISCLOSURE TIMELINE

09/08/2005  Initial vendor notification
09/09/2005  Initial vendor response
10/24/2005  Public disclosure

IX. CREDIT

iDEFENSE Labs is credited with the discovery of this vulnerability.

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X. LEGAL NOTICES

Copyright (c) 2005 iDEFENSE, Inc.

Permission is granted for the redistribution of this alert
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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.