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FreeBSD Security Advisory - Kernel Privilege Escalation

FreeBSD Security Advisory - Kernel Privilege Escalation
Posted Jun 12, 2012
Authored by Rafal Wojtczuk, John Baldwin | Site security.freebsd.org

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

tags | advisory, kernel, local
systems | freebsd
advisories | CVE-2012-0217
MD5 | 56d3bf6b6e660c92e8067bdb14796166

FreeBSD Security Advisory - Kernel Privilege Escalation

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=============================================================================
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)
2012-06-18 21:00:54 UTC (RELENG_8_1, 8.1-RELEASE-p12)
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/>.

0. Revision History

v1.0 2012-06-12 Initial release.
v1.1 2012-06-19 Corrected patch FreeBSD 8.1.

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.

[7.4, 8.3, 8.2, 9.0]
# fetch http://security.FreeBSD.org/patches/SA-12:04/sysret.patch
# fetch http://security.FreeBSD.org/patches/SA-12:04/sysret.patch.asc

[8.1]
# fetch http://security.FreeBSD.org/patches/SA-12:04/sysret-81.patch
# fetch http://security.FreeBSD.org/patches/SA-12:04/sysret-81.patch.asc

[8.1 if original sysret.patch has been applied]
# fetch http://security.FreeBSD.org/patches/SA-12:04/sysret-81-correction.patch
# fetch http://security.FreeBSD.org/patches/SA-12:04/sysret-81-correction.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 1.632.2.14.2.15
src/sys/conf/newvers.sh 1.83.2.10.2.16
src/sys/amd64/amd64/trap.c 1.332.2.10.2.3
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/ r237242
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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