CERT Advisory CA-1996-17 Vulnerability in Solaris vold

Original issue date: August 6, 1996
Last revised: October 20, 1997
Vendor information for Sun has been added to the UPDATES section.

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

The text of this advisory was originally released on August 2, 1996, as AUSCERT Advisory AL-96.04, developed by the Australian Computer Emergency Response Team. We are reprinting the AUSCERT advisory here with their permission. Only the contact information at the end has changed: AUSCERT contact information has been replaced with CERT/CC contact information.

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

AUSCERT has received a report of a vulnerability in the Sun Microsystems Solaris 2.x distribution involving the Volume Management daemon, vold(1M). This program is used to help manage CDROM and floppy devices.

This vulnerability may allow a local user to gain root privileges.

Exploit details involving this vulnerability have been made publicly available.

At this stage, AUSCERT is not aware of any official patches. AUSCERT recommends that sites take the actions suggested in Section 3 until official patches are available.

1. Description

The Volume Management daemon, vold(1M), manages the CDROM and floppy devices. For example, it provides the ability to automatically detect, and then mount, removable media such as CDROMs and floppy devices.

vold is part of the Solaris 2.x Volume Management package (SUNWvolu). It is executed as a background daemon on system startup and runs as root.

When vold detects that a CDROM or floppy has been inserted into a drive, it is configured to automatically mount the media, making it available to users. Part of this process includes the creation of temporary files, which are used to allow the Openwindows File Manager, filemgr(1), to determine that new media has been mounted. These files are created by the action_filemgr.so shared object which is called indirectly by vold through rmmount(1M). The handling of these files is not performed in a secure manner. As vold is configured to access these temporary files with root privileges, it may be possible to manipulate vold into creating or over-writing arbitrary files on the system.

This vulnerability requires that vold be running and media managed by vold, such as a CDROM or floppy, be physically loaded into a drive. Note that a local user need not have physical access to the media drive to exploit this vulnerability. It is enough to wait until somebody else loads the drive, exploiting the vulnerability at that time.

This vulnerability is known to be present in Solaris 2.4 and Solaris 2.5. Solaris distributions prior to Solaris 2.4 are also expected to be vulnerable.

2. Impact

Local users may be able to create or over-write arbitrary files on the system. This can be leveraged to gain root privileges.

3. Workaround

AUSCERT believes the workarounds given in Sections 3.1 or 3.2 will address this vulnerability. Vendor patches may also address this vulnerability in the future (Section 3.3).

3.1 Edit /etc/rmmount.conf

The temporary files which are susceptible to attack are created by the /usr/lib/rmmount/action_filemgr.so.1 shared object which is called indirectly by vold through rmmount(1M). rmmount(1M) can be configured so that it does not create the temporary files, thereby removing this vulnerability.

To our knowledge, configuring rmmount(1M) in this fashion will not affect the functionality of vold. It will, however, remove the ability of the Openwindows File Manager, filemgr(1), to automatically detect newly mounted media.

To prevent rmmount(1M) creating temporary files, sites must edit the /etc/rmmount.conf file and comment out (or remove) any entry which references action_filemgr.so.

The standard /etc/rmmount.conf contains the following entries which must be commented out (or deleted) to remove this vulnerability:

After applying this workaround, an example of /etc/rmmount.conf may look like:


        # @(#)rmmount.conf 1.2     92/09/23 SMI
        #
        # Removable Media Mounter configuration file.
        #

        # File system identification
        ident hsfs ident_hsfs.so cdrom
        ident ufs ident_ufs.so cdrom floppy pcmem
        ident pcfs ident_pcfs.so floppy pcmem

        # Actions
        #
        # Following two lines commented out to remove vold vulnerability
        #
        # action cdrom action_filemgr.so
        # action floppy action_filemgr.so

Note that vold does not have to be restarted for these changes to take effect.

3.2 Remove the Volume Management system

Sites who do not require the vold functionality should remove the complete set of Volume Management packages. These are SUNWvolg, SUNWvolu and SUNWvolr. These packages can be removed using pkgrm(1M).

3.3 Install vendor patches

Currently, AUSCERT is not aware of any official patches which address this vulnerability. When official patches are made available, AUSCERT suggests that they be installed.

AUSCERT wishes to thanks to Leif Hedstrom, Mark McPherson(QTAC), Marek Krawus(UQ), DFN-CERT and CERT/CC for their assistance in this matter.

UPDATES

Vendor Information

Below is information we have received from vendors. If you do not see your vendor's name below, contact the vendor directly for information.

Sun Microsystems, Inc.

Sun Microsystems has provided the following list of patches in response to this advisory:

Revision History

Oct. 20, 1997  Vendor information for Sun has been added to the UPDATES
                 section.
Sep. 24, 1997  Updated copyright statement
Aug. 30, 1996  Removed references to CA-96.17.README.
               Beginning of the advisory - removed AUSCERT advisory header
                 to avoid confusion.

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