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Category:   OS (UNIX)  >   FreeBSD Kernel Vendors:   FreeBSD
FreeBSD Kernel System Call Return Value Validation Flaw Lets Local Users Gain Elevated Privileges
SecurityTracker Alert ID:  1027164
SecurityTracker URL:  http://securitytracker.com/id/1027164
CVE Reference:   CVE-2012-0217   (Links to External Site)
Updated:  Jun 19 2012
Original Entry Date:  Jun 13 2012
Impact:   User access via local system
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 7.4, 8.1, 8.2, 8.3, 9.0
Description:   A vulnerability was reported in the FreeBSD Kernel. A local user can obtain elevated privileges on the target system.

A kernel-level sanity check does not properly validate user-supplied data on 64-bit CPUs. A local user can exploit this flaw to execute arbitrary code on the target system with elevated privileges.

FreeBSD/amd64 running on AMD CPUs is not affected.

Systems with 64 bit capable CPUs but running the 32 bit FreeBSD/i386 kernel are not affected.

Rafal Wojtczuk and John Baldwin reported this vulnerability.
Impact:   A local user can obtain elevated privileges on the target system.
Solution:   The vendor has issued a fix.

On June 19, 2012, the vendor issued an updated patch for FreeBSD 8.1.

The vendor's advisory is available at:

http://security.FreeBSD.org/advisories/FreeBSD-SA-12:04.sysret.asc
Vendor URL:  security.FreeBSD.org/advisories/FreeBSD-SA-12:04.sysret.asc (Links to External Site)
Cause:   Input validation error
Underlying OS:  

Message History:   None.

 Source Message Contents
Date:  Tue, 12 Jun 2012 13:26:33 +0000 (GMT)
Subject:  FreeBSD Security Advisory FreeBSD-SA-12:04.sysret

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

=============================================================================
FreeBSD-SA-12:04.sysret                                     Security Advisory
                                                          The FreeBSD Project

Topic:          Privilege escalation when returning from kernel

Category:       core
Module:         sys_amd64
Announced:      2012-06-12
Credits:        Rafal Wojtczuk, John Baldwin
Affects:        All supported versions of FreeBSD
Corrected:      2012-06-12 12:10:10 UTC (RELENG_7, 7.4-STABLE)
                2012-06-12 12:10:10 UTC (RELENG_7_4, 7.4-RELEASE-p9)
                2012-06-12 12:10:10 UTC (RELENG_8, 8.3-STABLE)
                2012-06-12 12:10:10 UTC (RELENG_8_3, 8.3-RELEASE-p3)
                2012-06-12 12:10:10 UTC (RELENG_8_2, 8.2-RELEASE-p9)
                2012-06-12 12:10:10 UTC (RELENG_8_1, 8.1-RELEASE-p11)
                2012-06-12 12:10:10 UTC (RELENG_9, 9.0-STABLE)
                2012-06-12 12:10:10 UTC (RELENG_9_0, 9.0-RELEASE-p3)
CVE Name:       CVE-2012-0217

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

The FreeBSD operating system implements a rings model of security, where
privileged operations are done in the kernel, and most applications
request access to these operations by making a system call, which puts
the CPU into the required privilege level and passes control to the
kernel.

II.  Problem Description

FreeBSD/amd64 runs on CPUs from different vendors.  Due to varying
behaviour of CPUs in 64 bit mode a sanity check of the kernel may be
insufficient when returning from a system call.

III. Impact

Successful exploitation of the problem can lead to local kernel privilege
escalation, kernel data corruption and/or crash.

To exploit this vulnerability, an attacker must be able to run code with user
privileges on the target system.

IV.  Workaround

No workaround is available.

However FreeBSD/amd64 running on AMD CPUs is not vulnerable to this
particular problem.

Systems with 64 bit capable CPUs, but running the 32 bit FreeBSD/i386
kernel are not vulnerable, nor are systems running on different
processor architectures.

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to 7-STABLE, 8-STABLE, or 9-STABLE,
or to the RELENG_7_4, RELENG_8_3, RELENG_8_2, RELENG_8_1, or RELENG_9_0
security branch dated after the correction date.

2) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to FreeBSD 7.4,
8.3, 8.2, 8.1 and 9.0 systems.

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

# fetch http://security.FreeBSD.org/patches/SA-12:04/sysret.patch
# fetch http://security.FreeBSD.org/patches/SA-12:04/sysret.patch.asc

b) Apply the patch.

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

c) Recompile your kernel as described in
<URL:http://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

3) To update your vulnerable system via a binary patch:

Systems running 7.4-RELEASE, 8.3-RELEASE, 8.2-RELEASE, 8.1-RELEASE,
or 9.0-RELEASE on the i386 or amd64 platforms can be updated via the
freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install

VI.  Correction details

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

CVS:

Branch                                                           Revision
  Path
- -------------------------------------------------------------------------
RELENG_7
  src/sys/amd64/amd64/trap.c                                   1.319.2.14
RELENG_7_4
  src/UPDATING                                            1.507.2.36.2.11
  src/sys/conf/newvers.sh                                  1.72.2.18.2.14
  src/sys/amd64/amd64/trap.c                               1.319.2.12.2.2
RELENG_8
  src/sys/amd64/amd64/trap.c                                   1.332.2.24
RELENG_8_3
  src/UPDATING                                             1.632.2.26.2.5
  src/sys/conf/newvers.sh                                   1.83.2.15.2.7
  src/sys/amd64/amd64/trap.c                               1.332.2.21.2.2
RELENG_8_2
  src/UPDATING                                            1.632.2.19.2.11
  src/sys/conf/newvers.sh                                  1.83.2.12.2.14
  src/sys/amd64/amd64/trap.c                               1.332.2.14.2.2
RELENG_8_1
  src/UPDATING                                            1.632.2.14.2.14
  src/sys/conf/newvers.sh                                  1.83.2.10.2.15
  src/sys/amd64/amd64/trap.c                               1.332.2.10.2.2
RELENG_9
  src/sys/amd64/amd64/trap.c                                    1.357.2.9
RELENG_9_0
  src/UPDATING                                              1.702.2.4.2.5
  src/sys/conf/newvers.sh                                    1.95.2.4.2.7
  src/sys/amd64/amd64/trap.c                                1.357.2.2.2.3
- -------------------------------------------------------------------------

Subversion:

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/7/                                                         r236953
releng/7.4/                                                       r236953
stable/8/                                                         r236953
releng/8.3/                                                       r236953
releng/8.2/                                                       r236953
releng/8.1/                                                       r236953
stable/9/                                                         r236953
releng/9.0/                                                       r236953
- -------------------------------------------------------------------------

VII. References

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2012-0217

The latest revision of this advisory is available at
http://security.FreeBSD.org/advisories/FreeBSD-SA-12:04.sysret.asc
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