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The U.S. Department of Energy
Computer Incident Advisory Capability
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INFORMATION BULLETIN
Vulnerability in WorkMan Program
August 29, 1996 15:00 GMT Number G-42
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PROBLEM: When the "WorkMan" compact disc playing program is installed
set-user-id "root", it can be used to make any file on the
system world-writable.
PLATFORM: Linux, UNIX System V Release 4.0 (and derivatives).
DAMAGE: A non-privileged user can use "WorkMan" to make any file on the
system world-writable, and then modify that file's contents.
This vulnerbility can allow the user to create accounts,
destroy log files, and perform other unauthorized actions.
SOLUTION: Apply the patches listed in the vendor bulletin below.
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VULNERABILITY This vulnerability is becoming widely known.
ASSESSMENT:
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[Begin IBM Bulletin]
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- - ---EXTERNAL RELEASE---EXTERNAL RELEASE---EXTERNAL RELEASE---EXTERNAL RELEASE
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EMERGENCY RESPONSE SERVICE
SECURITY VULNERABILITY ALERT
28 August 1996 18:00 GMT Number: ERS-SVA-E01-1996:005.1
=============================================================================
VULNERABILITY SUMMARY
VULNERABILITY: When the "WorkMan" compact disc playing program is installed
set-user-id "root," it can be used to make any file on the
system world-writable.
PLATFORMS: Linux, UNIX System V Release 4.0 (and derivatives)
SOLUTION: Remove the set-user-id bit from the "workman" program.
THREAT: A non-privileged user can use "WorkMan" to make any file on
the system world-writable, and then modify that file's
contents.
=============================================================================
DETAILED INFORMATION
NOTE: This advisory is NOT a re-hash of the problem reported on several lists
earlier this week by a group calling itself "r00t." The vulnerability
described by "r00t" is essentially a subset of the problem described in
this alert.
I. Description
"WorkMan" is a popular program used for playing audio compact disks on local
workstation CD-ROM drives that is widely available from many sites around the
Internet. Versions of "WorkMan" are also included with some operating system
distributions, such as Linux.
On systems where "WorkMan" was built and installed using the procedures that
are given in "Makefile.linux" or "Makefile.svr4" (in general, this means on
Linux systems and UNIX System V Release 4.0 systems), the "workman" program
is installed set-user-id "root." This means that when the program is run,
it will execute with super-user permissions.
In order to allow signals to be sent to it, "WorkMan" writes its process-id
to a file called "/tmp/.wm_pid." The "-p" option to the program allows the
user to specify a different file name in which to record this information.
When a file is specified with "-p", "WorkMan" simply attempts to create and/or
truncate the file, and if this succeeds, "WorkMan" changes the permissions on
the file so that it is world-readable and world-writable.
In the general case, when "WorkMan" is installed without the set-user-id bit
set, the normal file access permissions provided by the operating system will
prevent users from creating or truncating files they are not authorized to
create or truncate. However, when "WorkMan" is installed set-user-id "root,"
this process breaks down (because "root" is allowed to create/truncate any
file).
II. Impact
A user executing a set-user-id "root" version of "WorkMan" can use the "-p"
option to create a file anywhere in the file system, or to truncate any file
in the file system. More importantly, the file specified with "-p" will be
world-readable and world-writable when "WorkMan" is finished. This can enable
the user to create accounts, destroy log files, and perform other unauthorized
actions.
III. Solutions
"WorkMan" does not require the set-user-id bit to work; it is installed this
way only on systems that do not make the CD-ROM device file world-readable
by default.
This vulnerability can be alleviated by:
1) Removing the set-user-id bit from the "WorkMan" program, via a command
such as
chmod u-s /usr/local/bin/workman
and
2) Making the CD-ROM device world-readable, via a command such as
chmod +r /dev/cdrom
Note that on multi-user systems, part (2) of the above procedure will allow
any user to access the contents of the disc installed in the CD-ROM; this
may not be desirable in all environments.
IV. Acknowledgements
IBM-ERS would like to thank the IBM Global Security Analysis Laboratory at the
IBM T. J. Watson Research Center for their discovery of this vulnerability,
bringing it to our attention, providing the steps to fix it, and assistance in
developing this alert.
UNIX is a technology trademark of X/Open Company, Ltd.
===============================================================================
[End IBM Bulletin]
_______________________________________________________________________________
CIAC wishes to acknowledge the contributions of IBM for the
information contained in this bulletin.
_______________________________________________________________________________
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---Murat Arslan