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  • CERT Advisory CA-1996-23 Vulnerability in WorkMan

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Original issue date: October 28, 1996
Last revised: September 24, 1997
Updated copyright statement

A complete revision history is at the end of this file.

The original technical content for this advisory was published by the IBM-ERS response team and is used here with their permission.

There is a vulnerability in the WorkMan compact disc-playing program that affects UNIX System V Release 4.0 and derivatives and Linux systems. When the program is installed set-user-id root, it can be used to make any file on the system world-writable.

To address this problem, you should remove the set-user-id bit from the program.

We will update this advisory as we receive additional information. Please check advisory files regularly for updates that relate to your site.

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).

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.

Note: The vulnerability described by "r00t" on several mailing lists is not the same one that we describe in this advisory.

II. Impact

A user with access to an account on the system can use the "-p" option to create a file anywhere in the file system or to truncate any file in the file system. 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. Solution

1. Remove the set-user-id bit from the WorkMan program using a command such as
          chmod u-s /usr/local/bin/workman
2. Make the CD-ROM device world-readable using a command such as
          chmod +r /dev/cdrom
On multi-user systems, Step 2 will allow any user to access the contents of the disc installed in the CD-ROM; this may not be desirable in all environments.

The vulnerability described in this advisory is related to the WorkMan program, not to the products of particular vendors. However, if a vendor sends us advice for their users, we will put it in Appendix A.

Appendix A - Vendor Information

This appendix contains advice vendors wish to offer their users. Note that the vulnerability described in this advisory is related to the WorkMan program, not particular vendors' products.

Sun Microsystems, Inc.

Sun does not recommend that workman and other utility programs be installed setuid root (or anything else) unless that step is absolutely necessary. Programs which were not designed with security in mind (and most non-setuid programs are not) are unlikely to have built-in allowances for abuse. The proper way to allow such programs to work is to install them as unprivileged, ordinary software, then modify device permissions as necessary to allow them to function.

When an unprivileged users executes a recent version of the workman program on a properly configured Solaris 2.x system, a message similar to the following appears. (Ellipses added to save space.)

As root, please run

          chmod 666 /devices/iommu@0,,0:c,raw
to give yourself permission to access the CD-ROM device.

That's pretty good advice. Of course, if you don't want to give every user access to the contents of a CD (which will sometimes be data or software, and sometimes music) such permissions are not appropriate.

The CERT Coordination Center thanks IBM-ERS for permission to reproduce the technical content in their IBM Emergency Response Service Security Vulnerability Alert ERS-SVA-E01-1996:005.1. These alerts are copyrighted 1996 International Business Machines Corporation.

Copyright 1996 Carnegie Mellon University.

Revision History
Sep. 24, 1997  Updated copyright statement
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