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FreeBSD-SA-08:01.pty                                        Security Advisory
                                                          The FreeBSD Project

Topic:          pty snooping

Category:       core
Module:         libc_stdlib / libutil
Announced:      2008-01-14
Credits:        John Baldwin
Affects:        FreeBSD 5.0 and later.
Corrected:      2008-01-14 22:57:45 UTC (RELENG_7, 7.0-PRERELEASE)
                2008-01-14 22:55:54 UTC (RELENG_7_0, 7.0-RC2)
                2008-01-14 22:56:05 UTC (RELENG_6, 6.3-PRERELEASE)
                2008-01-14 22:56:18 UTC (RELENG_6_3, 6.3-RELEASE)
                2008-01-14 22:56:44 UTC (RELENG_6_2, 6.2-RELEASE-p10)
                2008-01-14 22:56:56 UTC (RELENG_6_1, 6.1-RELEASE-p22)
                2008-01-14 22:57:06 UTC (RELENG_5, 5.5-STABLE)
                2008-01-14 22:57:19 UTC (RELENG_5_5, 5.5-RELEASE-p18)
CVE Name:       CVE-2008-0216, CVE-2008-0217

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:http://security.FreeBSD.org/>.

I.   Background

pt_chown is a setuid root support utility used by grantpt(3) to change
ownership of a tty.

openpty(3) is a support function in libutil which is used to obtain a
pseudo-terminal.

script(1) is a utility which makes a typescript of everything printed
on a terminal.

II.  Problem Description

Two issues exist in the FreeBSD pty handling.

If openpty(3) is called as non-root user the newly created
pseudo-terminal is world readable and writeable.  While this is
documented to be the case, script(1) still uses openpty(3) and
script(1) may be used by non-root users [CVE-2008-0217].

The ptsname(3) function incorrectly extracts two characters from the
name of a device node in /dev without verifying that it's actually
operating on a valid pty which the calling user owns.  pt_chown uses
the bad result from ptsname(3) to change ownership of a pty to the
user calling pt_chown [CVE-2008-0216].

III. Impact

If an unprivileged user is running script(1), or another program which
uses openpty(3), an attacker may snoop text which is printed to the
users terminal.

If a malicious user has read access to a device node with characters
in the device name that match the name of a pty, then the malicious user
can read the content of the pty from another user.  The malicious user
can open a lot of tty's resulting in a high probabilty of a new user
obtaining the pty name of a "vulnerable" pty.

NOTE WELL: If a user snoops a pty the snooped text will not be shown
to the real user, which in many cases mean the real owner of the pty
will be able to know the attack is taking place.

IV.  Workaround

Do not run script(1) as a non-root user.

The ptsname(3) issue only affects FreeBSD 6.0 and newer.

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to 5-STABLE, 6-STABLE, or
7.0-PRERELEASE, or to the RELENG_7_0, RELENG_6_3, RELENG_6_2,
RELENG_6_1, or RELENG_5_5 security branch dated after the correction
date.

2) To patch your present system:

The following patches have been verified to apply to FreeBSD 5.5, 6.1,
6.2, 6.3, and 7.0 systems.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

[FreeBSD 5.5]
# fetch http://security.FreeBSD.org/patches/SA-08:01/pty5.patch
# fetch http://security.FreeBSD.org/patches/SA-08:01/pty5.patch.asc

[FreeBSD 6.x]
# fetch http://security.FreeBSD.org/patches/SA-08:01/pty6.patch
# fetch http://security.FreeBSD.org/patches/SA-08:01/pty6.patch.asc

[FreeBSD 7.0]
# fetch http://security.FreeBSD.org/patches/SA-08:01/pty7.patch
# fetch http://security.FreeBSD.org/patches/SA-08:01/pty7.patch.asc

b) Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile the operating system as described in
<URL: http://www.freebsd.org/handbook/makeworld.html> and reboot the
system.

VI.  Correction details

The following list contains the revision numbers of each file that was
corrected in FreeBSD.

Branch                                                           Revision
  Path
- -------------------------------------------------------------------------
RELENG_5
  src/lib/libutil/pty.c                                          1.15.4.1
RELENG_5_5
  src/UPDATING                                            1.342.2.35.2.18
  src/sys/conf/newvers.sh                                  1.62.2.21.2.20
  src/lib/libutil/pty.c                                         1.15.16.1
RELENG_6
  src/lib/libc/stdlib/grantpt.c                                   1.4.2.2
  src/lib/libutil/pty.c                                         1.15.10.2
RELENG_6_3
  src/UPDATING                                             1.416.2.37.2.3
  src/sys/conf/newvers.sh                                   1.69.2.15.2.3
  src/lib/libc/stdlib/grantpt.c                                  1.4.10.2
  src/lib/libutil/pty.c                                         1.15.20.2
RELENG_6_2
  src/UPDATING                                            1.416.2.29.2.13
  src/sys/conf/newvers.sh                                  1.69.2.13.2.13
  src/lib/libc/stdlib/grantpt.c                                   1.4.8.1
  src/lib/libutil/pty.c                                         1.15.18.1
RELENG_6_1
  src/UPDATING                                            1.416.2.22.2.24
  src/sys/conf/newvers.sh                                  1.69.2.11.2.24
  src/lib/libc/stdlib/grantpt.c                                   1.4.6.1
  src/lib/libutil/pty.c                                         1.15.14.1
RELENG_7
  src/lib/libc/stdlib/grantpt.c                                   1.7.2.4
  src/lib/libutil/pty.c                                          1.17.2.3
RELENG_7_0
  src/UPDATING                                              1.507.2.3.2.1
  src/sys/conf/newvers.sh                                    1.72.2.5.2.2
  src/lib/libc/stdlib/grantpt.c                               1.7.2.2.2.2
  src/lib/libutil/pty.c                                      1.17.2.2.2.1
- -------------------------------------------------------------------------

VII. References

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-0216
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-0217

The latest revision of this advisory is available at
http://security.FreeBSD.org/advisories/FreeBSD-SA-08:01.pty.asc
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