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Category:   OS (UNIX)  >   FreeBSD Kernel Vendors:   FreeBSD
FreeBSD Kernel ELF Header Parsing Error Lets Local Users Obtain Memory Contents and Cause the Target System to Crash
SecurityTracker Alert ID:  1041646
SecurityTracker URL:  http://securitytracker.com/id/1041646
CVE Reference:   CVE-2018-6924   (Links to External Site)
Date:  Sep 12 2018
Impact:   Denial of service via local system, Disclosure of system information
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 10.4, 11.1, 11.2
Description:   A vulnerability was reported in FreeBSD Kernel. A local user can cause denial of service conditions on the target system. A local user can obtain potentially sensitive information from system memory.

A local user can execute a specially crafted ELF binary to obtain potentially sensitive information from system memory on the target system or cause the target system to crash.

Thomas Barabosch, Fraunhofer FKIE, and Mark Johnston reported this vulnerability.

Impact:   A local user can cause denial of service conditions on the target system.

A local user can obtain potentially sensitive information from system memory on the target system.

Solution:   FreeBSD has issued a fix.

The FreeBSD advisory is available at:

https://security.FreeBSD.org/advisories/FreeBSD-SA-18:12.elf.asc

Vendor URL:  security.FreeBSD.org/advisories/FreeBSD-SA-18:12.elf.asc (Links to External Site)
Cause:   Input validation error

Message History:   None.


 Source Message Contents

Subject:  FreeBSD Security Advisory FreeBSD-SA-18:12.elf

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512

=============================================================================
FreeBSD-SA-18:12.elf                                        Security Advisory
                                                          The FreeBSD Project

Topic:          Improper ELF header parsing

Category:       core
Module:         kernel
Announced:      2018-09-12
Credits:        Thomas Barabosch, Fraunhofer FKIE; Mark Johnston
Affects:        All supported versions of FreeBSD.
Corrected:      2018-09-12 05:02:11 UTC (stable/11, 11.1-STABLE)
                2018-09-12 05:07:35 UTC (releng/11.2, 11.2-RELEASE-p3)
                2018-09-12 05:07:35 UTC (releng/11.1, 11.1-RELEASE-p14)
                2018-09-12 05:03:30 UTC (stable/10, 10.4-STABLE)
                2018-09-12 05:07:35 UTC (releng/10.4, 10.4-RELEASE-p12)
CVE Name:       CVE-2018-6924

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

I.   Background

To execute a binary the kernel must parse the ELF header to determine the
entry point address, the program interpreter, and other parameters.

II.  Problem Description

Insufficient validation was performed in the ELF header parser, and malformed
or otherwise invalid ELF binaries were not rejected as they should be.

III. Impact

Execution of a malicious ELF binary may result in a kernel crash or may
disclose kernel memory.

IV.  Workaround

No workaround is available.

V.   Solution

Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date, and
reboot.

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

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install
# shutdown -r +30 "Rebooting for security update"

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

The following patches have been verified to apply to the applicable
FreeBSD release branches.

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

# fetch https://security.FreeBSD.org/patches/SA-18:12/elf.patch
# fetch https://security.FreeBSD.org/patches/SA-18:12/elf.patch.asc
# gpg --verify elf.patch.asc

b) Apply the patch.  Execute the following commands as root:

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

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

VI.  Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/10/                                                        r338605
releng/10.4/                                                      r338606
stable/11/                                                        r338604
releng/11.1/                                                      r338606
releng/11.2/                                                      r338606
- -------------------------------------------------------------------------

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-6924>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-18:12.elf.asc>
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