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Category:   OS (UNIX)  >   FreeBSD Kernel Vendors:   FreeBSD
FreeBSD NFS Server Code Flaws Let Remote Users Execute Arbitrary Code
SecurityTracker Alert ID:  1042164
SecurityTracker URL:  http://securitytracker.com/id/1042164
CVE Reference:   CVE-2018-17157, CVE-2018-17158, CVE-2018-17159   (Links to External Site)
Date:  Nov 28 2018
Impact:   Execution of arbitrary code via network, User access via network
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 11.2
Description:   Several vulnerabilities were reported in FreeBSD Kernel. A remote user can cause arbitrary code to be executed on the target user's system.

A remote user can create specially crafted network file system (NFS) content that, when loaded by the target user, either remotely or locally, will trigger a flaw in the FreeBSD NFS server code and cause the target system to crash or potentially execute arbitrary code.

Systems that do not provide NFS services are not affected.

Jakub Jirasek, Secunia Research at Flexera reported these vulnerabilities.

Impact:   A remote user can create content that will execute arbitrary code on the target user's system.
Solution:   FreeBSD has issued a fix.

The FreeBSD advisory is available at:

https://security.FreeBSD.org/advisories/FreeBSD-SA-18:13.nfs.asc

Vendor URL:  security.FreeBSD.org/advisories/FreeBSD-SA-18:13.nfs.asc (Links to External Site)
Cause:   Not specified

Message History:   None.


 Source Message Contents

Subject:  FreeBSD Security Advisory FreeBSD-SA-18:13.nfs

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

=============================================================================
FreeBSD-SA-18:13.nfs                                        Security Advisory
                                                          The FreeBSD Project

Topic:          Multiple vulnerabilities in NFS server code

Category:       core
Module:         nfs
Announced:      2018-11-27
Credits:        Jakub Jirasek, Secunia Research at Flexera
Affects:        All supported versions of FreeBSD.
Corrected:      2018-11-23 20:41:54 UTC (stable/11, 11.2-STABLE)
                2018-11-27 19:42:16 UTC (releng/11.2, 11.2-RELEASE-p5)
CVE Name:       CVE-2018-17157, CVE-2018-17158, CVE-2018-17159

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

The Network File System (NFS) allows a host to export some or all of its file
systems so that other hosts can access them over the network and mount them
as if they were local.  FreeBSD includes both server and client
implementations of NFS.

II.  Problem Description

Insufficient and improper checking in the NFS server code could cause a
denial of service or possibly remote code execution via a specially crafted
network packet.

III. Impact

A remote attacker could cause the NFS server to crash, resulting in a denial
of service, or possibly execute arbitrary code on the server. 

IV.  Workaround

No workaround is available, but systems that do not provide NFS services are
not vulnerable.

Additionally, it is highly recommended the NFS service port (default port
number 2049) is protected via a host or network based firewall to prevent
arbitrary, untrusted clients from being able to connect.

V.   Solution

Perform one of the following:

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

Afterward, reboot the system.

2) 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

Afterward, reboot the system.

3) 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.

[FreeBSD 11.2]
# fetch https://security.FreeBSD.org/patches/SA-18:13/nfs.patch
# fetch https://security.FreeBSD.org/patches/SA-18:13/nfs.patch.asc
# gpg --verify nfs.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/11/                                                        r340854
releng/11.2/                                                      r341088
- -------------------------------------------------------------------------

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://www.flexerasoftware.com/enterprise/company/about/secunia-research/>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-17157>
<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-17158>
<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-17159>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-18:13.nfs.asc>
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