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CERT Advisory 096
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CERT(sm) Advisory CA-95:09
Original issue date: August 29, 1995
Last revised: August 30, 1996
Information previously in the README was inserted
into the advisory. Updated version number of AUSCERT checklist
and the appendix.
A complete revision history is at the end of this file.
Topic: Solaris ps Vulnerability
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The text of this advisory is taken primarily
from AUSCERT advisory AA-95.07, with their permission.
A vulnerability exists in Solaris systems that allows a race condition to be
exploited to gain root access. The essential problem is that the ps(1)
program maintains a data file in the /tmp directory, and the /tmp directory is
world-writable, allowing users to delete other users' files in /tmp. This
vulnerability affects Solaris 2.x (SunOS 5.x) systems.
An exploit program for this vulnerability has been published. We urge
you to take the actions described in Section III as soon as possible.
We will update this advisory as we receive additional information.
Please check advisory files regularly for updates that relate to your site.
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I. Description
A race condition exists in at least one Solaris 2.x (SunOS 5.x) system
program that can be exploited to gain root access if the user has access
to the temporary files. Access to temporary files may be obtained if the
permissions on the /tmp and /var/tmp directories are set incorrectly.
The permissions on the /tmp directory are often reset incorrectly by
the system if tmpfs (which is mounting swap as /tmp) is in use.
II. Impact
Users logged in to the system may gain unauthorized root privileges.
III. Solution
A. Determine if your system is vulnerable
To determine if you are running tmpfs, the following command can be
used to verify if the file system for /tmp is swap:
% /usr/sbin/df -k /tmp
Filesystem kbytes used avail capacity Mounted on
swap 28348 12 28336 0% /tmp
or look in the file /etc/vfstab for the configuration line:
#device device mount FS fsck mount mount
#to mount to fsck point type pass at boot options
swap - /tmp tmpfs - yes -
If either of these two conditions exist, then you are running tmpfs
and the system may automatically reset the permission bits of /tmp at
the next reboot.
To verify if your configuration is currently vulnerable, the
following command may be used:
% /usr/bin/ls -ld /tmp
drwxrwxrwt 2 root root 61 Aug 15 12:12 /tmp
If the sticky bit (t) is not set (it will be an x), then the
system is vulnerable. In addition, we recommend that the owner
and group for /tmp be changed to root and root, respectively.
B. Perform the following workarounds
These workarounds have been verified with Sun Microsystems. Apply
these workarounds until you an install a patch. (Patch information is
in Sec. C. below.)
1. Immediate - fix /tmp permissions
A workaround that takes effect immediately is to set the sticky bit
on the /tmp directory using the following command as root:
# /usr/bin/chmod 1777 /tmp
Note that this command must be performed after each reboot if you
are mounting swap as /tmp (using tmpfs).
In addition, the ownership and group membership of the /tmp
directory should be verified using /usr/bin/ls -ld /tmp, and if
incorrect may be reset by:
# /usr/bin/chown root /tmp
# /usr/bin/chgrp root /tmp
The AUSCERT UNIX Security Checklist addresses this issue in
Section 5.5. This section is reproduced in the appendix of this
advisory. The entire AUSCERT checklist may be obtained from these
locations.
Sites outside of Australia should use the info.cert.org FTP site.
ftp://info.cert.org/pub/tech_tips/AUSCERT_checklist_1.1
ftp://ftp.auscert.org.au/pub/auscert/papers/unix_security_checklist_1.1
2. Permanent - make the above change to /tmp permissions permanent
The change noted in item B.1 above will be lost upon
reboot. To make the changes permanent, create the
following script as /etc/init.d/tmpfsfix:
-----------------------------cut here--8<----------------------------
#!/bin/sh
if [ -d /tmp ]
then
/usr/bin/chmod 1777 /tmp
/usr/bin/chgrp root /tmp
/usr/bin/chown root /tmp
fi
------------------------------cut here---8<--------------------------
After creating this file, the following commands should be issued
as root to make the file executable, set appropriate owner and group,
and create the necessary symbolic link to ensure that it is executed
upon reboot appropriately:
# /usr/bin/ln -s /etc/init.d/tmpfsfix /etc/rc2.d/S06tmpfix
# /usr/bin/chmod 744 /etc/init.d/tmpfsfix
# /usr/bin/chown root /etc/init.d/tmpfsfix
# /usr/bin/chgrp sys /etc/init.d/tmpfsfix
# /bin/rm -f /etc/rc3.d/S79tmpfix
If you have done item B.1 above, you can reboot at your leisure.
Otherwise, reboot your system now. In either case, verify the
permissions of /tmp immediately after your next system reboot.
3. Check /var/tmp permissions
We recommend that you also check and correct the /var/tmp
directory. Note that this directory is not usually mounted as
tmpfs, so it normally would not be subject to automatic resetting
of its permission bits on reboot.
% /usr/bin/ls -ld /var/tmp
drwxrwxrwt 2 root root 512 Aug 15 11:35 /var/tmp
C. Install a vendor patch
On September 20, 1995, Sun Microsystems, Inc., provided the following
information in their advisory.
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Begin Text provided by vendor
II. Announcement of patches for Solaris 2.x "ps_data" vulnerability
A. Patch list
We have produced patches for the versions of SunOS shown below.
OS version Patch ID Patch File Name
---------- --------- ---------------
5.3 101545-02 101545-02.tar.Z
5.4 102711-01 102711-01.tar.Z
5.4_x86 102712-01 102712-01.tar.Z
B. Patch notes
1. SunOS 4.1.x systems are not affected by this bug.
2. The fix has been applied to the upcoming version of Solaris.
III. Checksum Table
In the checksum table we show the BSD and SVR4 checksums and MD5
digital signatures for the compressed tar archives.
File BSD SVR4 MD5
Name Checksum Checksum Digital Signature
--------------- ----------- ---------- --------------------------------
101545-02.tar.Z 41218 77 47754 153 A8FB866780E7207D26CF16210BCFDC83
102711-01.tar.Z 17256 69 20376 138 98A449372C5ABBDB7C37B08BFE0E6ED7
102712-01.tar.Z 29867 68 56717 136 E324004BB8C09990B2790CB5D29D3AF5
The checksums shown above are from the BSD-based checksum
(on 4.1.x, /bin/sum; on Solaris 2.x, /usr/ucb/sum) and from
the SVR4 version on Solaris 2.x (/usr/bin/sum).
End Text provided by vendor
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..............................................................................
Appendix: Excerpt from AUSCERT UNIX Security Checklist (Version 1.1)
5.5 File Permissions
* ENSURE that the permissions of /etc/utmp are set to 644.
* ENSURE that the permissions of /etc/sm and /etc/sm.bak are set to
2755.
* ENSURE that the permissions of /etc/state are set to 644.
* ENSURE that the permissions of /etc/motd and /etc/mtab are set to 644.
* ENSURE that the permissions of /etc/syslog.pid are set to 644.
[NOTE: this may be reset each time you restart syslog.]
* DO consider removing read access to files that users do not need to
access.
* ENSURE that the kernel (e.g., /vmunix) is owned by root, has group set
to 0 (wheel on SunOS) and permissions set to 644.
* ENSURE that /etc, /usr/etc, /bin, /usr/bin, /sbin, /usr/sbin, /tmp and
/var/tmp are owned by root and that the sticky-bit is set on /tmp and
on /var/tmp (see G.14). Refer to the AUSCERT Advisory AA-95:05 (see
A.1).
* ENSURE that there are no unexpected world writable files or
directories on your system.
See G.15 for example commands to find group and world writable files
and directories.
* CHECK that files which have the SUID or SGID bit enabled, should have
it enabled (see G.16).
* ENSURE the umask value for each user is set to something sensible
like 027 or 077.
(Refer to section E.1 for a shell script to check this).
* ENSURE all files in /dev are special files.
Special files are identified with a letter in the first position
of the permissions bits. See G.17 for a command to find files in
/dev which are not special files or directories.
Note: Some systems have directories and a shell script in /dev
which may be legitimate. Please check the manual pages for more
information.
* ENSURE that there are no unexpected special files outside /dev.
See G.18 for a command to find any block special or character
special files.
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The CERT Coordination Center staff thanks AUSCERT, the Australian response
team, for their permission to reuse text from their advisory AA-95.07 and
for their cooperation and assistance.
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If you believe that your system has been compromised, contact the CERT
Coordination Center or your representative in the Forum of Incident
Response and Security Teams (FIRST).
If you wish to send sensitive incident or vulnerability information to
CERT staff by electronic mail, we strongly advise that the email be
encrypted. The CERT Coordination Center can support a shared DES key, PGP
(public key available via anonymous FTP on info.cert.org), or PEM (contact
CERT staff for details).
Internet email: cert@cert.org
Telephone: +1 412-268-7090 (24-hour hotline)
CERT personnel answer 8:30 a.m.-5:00 p.m. EST(GMT-5)/EDT(GMT-4),
and are on call for emergencies during other hours.
Fax: +1 412-268-6989
Postal address: CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh, PA 15213-3890
USA
CERT advisories and bulletins are posted on the USENET newsgroup
comp.security.announce. If you would like to have future advisories and
bulletins mailed to you or to a mail exploder at your site, please send mail
to cert-advisory-request@cert.org.
Past CERT publications, information about FIRST representatives, and
other information related to computer security are available for anonymous
FTP from info.cert.org.
This material may be reproduced and distributed without permission provided it
is used for noncommercial purposes, and the CERT Coordination Center and
AUSCERT are acknowledged.
CERT is a service mark of Carnegie Mellon University.
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UPDATES
If anyone has trouble retrieving the electronic file CA-95:09.Solaris.ps.vul,
they should use the file name CA-95:09.Solaris-ps.vul.
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Revision history
Aug. 30, 1996 Information previously in the README was inserted
into the advisory. Updated version number of AUSCERT checklist
and the appendix.
Sep. 20, 1995 Sec. III.A.1 - corrected the command and explanation for
checking your configuration.
Sec. III.B.1 - corrected commands for verifying ownership and
group membership.
Sec. III.B.2 - replaced this section, which was incorrect.
Sec. III.B.3 - replaced the text and command.
Sec. III.C - added this section, which contains Sun patch
information.
Appendix - corrected item 10.
Updates section - added a note about the file name.
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