@stake Advisory: MacOS X TruBlueEnvironment Privilege Escalation Attack

2003-02-1500:00:00

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                            @stake, Inc.
                          www.atstake.com

                         Security Advisory

Advisory Name: TruBlueEnvironment Privilege Escalation Attack
Release Date: 02/14/2003
Application: TruBlueEnvironment
Platform: MacOS X (10.2.3 and below)
Severity: Local users can gain root privileges
Author: Dave G. <[email protected]>
Vendor Status: updated version of OS available
CVE Candidate: CAN-2003-0088
Reference: www.atstake.com/research/advisories/2003/a021403-1.txt

Overview:

TruBlueEnvironment is part of the MacOS Classic Emulator. It
is setuid root and installed by default. By setting certain
environment variables, it is possible to overwrite any file on the
system, or create arbitrary files owned as root with the attacker's
umask. This vulnerability can be leveraged to create files that will
get executed by root through the cron facility.

Details:

TruBluEnvironment uses an environment variable to determine where to
write out debugging information. Local users can set this to
environment variable to point at any file on the filesystem. If the
file exists, it will be reset to zero bytes. If the file does not
exist, it will be created with the umask inherited from the calling
process. While attackers cannot create files with execute
permissions set, they can create files that are world writable.

Under MacOS X, this vulnerability can be used to create files that
will be run automatically via cron. By default, cron will launch
maintenance scripts using the periodic command. This command will
take several files and either 'source' them or run them through a
shell interpreter. Since these scripts are running as root, it is
possible to obtain administrator privileges on any MacOS X system
running cron and TruBlueEnvironment.

Vendor Response:

Classic: The Mac OS X 10.2.4 release fixes CAN-2003-0088, where an
attacker may change an environment variable to create arbitrary
files or overwrite existing files, which could lead to obtaining
elevated privileges. Credit to Dave G. from @stake, Inc. for
discovering this issue.

Recommendation:

If possible upgrade to Mac OS X 10.2.4. Another solution is to
restrict access to the TruBlueEnvironment(*) executable, or remove
it entirely if it is not being used. One approach to restrict
TruBlueEnvironment executable,and only allow a specific group to
execute the application. The following commands will restrict
access to the 'admin' group:

sudo chown .admin /System/Library/CoreServices/Classic\
Startup.app/Contents/Resources/TruBlueEnvironment

sudo chmod 4750 /System/Library/CoreServices/Classic\
Startup.app/Contents/Resources/TruBlueEnvironment

(*) Located in /System/Library/CoreServices/Classic
Startup.app/Contents/Resources/TruBlueEnvironment

Common Vulnerabilities and Exposures (CVE) Information:

The Common Vulnerabilities and Exposures (CVE) project has assigned
the following names to these issues. These are candidates for
inclusion in the CVE list (http://cve.mitre.org), which standardizes
names for security problems.

CAN-2003-0088

@stake Vulnerability Reporting Policy:
http://www.atstake.com/research/policy/

@stake Advisory Archive:
http://www.atstake.com/research/advisories/

PGP Key:
http://www.atstake.com/research/pgp_key.asc

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