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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 .
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
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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