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Category:   Application (VPN)  >   OpenSSH Vendors:   OpenSSH.org
(FreeBSD Issues Fix) OpenSSH Multiple Flaws Let Remote Authenticated Users Gain Elevated Privileges and Local Privileged Users Obtain Host Private Keys
SecurityTracker Alert ID:  1037577
SecurityTracker URL:  http://securitytracker.com/id/1037577
CVE Reference:   CVE-2016-10009, CVE-2016-10010   (Links to External Site)
Date:  Jan 11 2017
Impact:   Denial of service via network, Disclosure of authentication information, Execution of arbitrary code via network, Modification of system information, Modification of user information, Root access via local system, User access via network
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): prior to 7.4
Description:   Multiple vulnerabilities were reported in OpenSSH. A remote authenticated user can gain elevated privileges. A remote authenticated user can write files on the target system. A local user can obtain private keys on the target system.

A remote authenticated user with control of a sshd service can return a request to the target ssh-agent to load a specially crafted PKCS#11 module across a forwarded agent channel and execute arbitrary code on or write files to the target system running the ssh-agent [CVE-2016-10009].

A user that can exploit a separate vulnerability on sshd may be able to gain root privileges via a forwarded Unix-domain socket [CVE-2016-10010]. Systems with privilege separation disabled are affected.

A local privileged user may be able to exploit a privilege separation flaw to obtain host private key material [CVE-2016-10011].

A user that can exploit a separate vulnerability on sshd may be able to gain elevated privileges due to a flaw in boundary checks in the shared memory manager that may be skipped by some optimizing compilers [CVE-2016-10012].

A remote user may be able to bypass address-based access controls if the AllowUser directive is configured with invalid CIDR address ranges.

Jann Horn of Project Zero, Guido Vranken, and Laurence Parry reported these vulnerabilities.

Impact:   A remote authenticated user can gain elevated privileges on the target system.

A remote authenticated user can modify files on the target system.

A local user can obtain passwords on the target system.

Solution:   FreeBSD has issued a fix for CVE-2016-10009 and CVE-2016-10010.

The FreeBSD advisory is available at:

https://security.FreeBSD.org/advisories/FreeBSD-SA-17:01.openssh.asc

Vendor URL:  security.FreeBSD.org/advisories/FreeBSD-SA-17:01.openssh.asc (Links to External Site)
Cause:   Access control error, Boundary error
Underlying OS:  UNIX (FreeBSD)
Underlying OS Comments:  10.3, 11.0

Message History:   This archive entry is a follow-up to the message listed below.
Dec 19 2016 OpenSSH Multiple Flaws Let Remote Authenticated Users Gain Elevated Privileges and Local Privileged Users Obtain Host Private Keys



 Source Message Contents

Subject:  FreeBSD Security Advisory FreeBSD-SA-17:01.openssh

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

=============================================================================
FreeBSD-SA-17:01.openssh                                    Security Advisory
                                                          The FreeBSD Project

Topic:          OpenSSH multiple vulnerabilities

Category:       contrib
Module:         OpenSSH
Announced:      2017-01-11
Affects:        All supported versions of FreeBSD.
Corrected:      2017-01-11 05:56:40 UTC (stable/11, 11.0-STABLE)
                2017-01-11 06:01:23 UTC (releng/11.0, 11.0-RELEASE-p7)
                2017-01-11 05:56:40 UTC (stable/10, 10.3-STABLE)
                2017-01-11 06:01:23 UTC (releng/10.3, 10.3-RELEASE-p16)
CVE Name:       CVE-2016-10009, CVE-2016-10010

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

OpenSSH is an implementation of the SSH protocol suite, providing an
encrypted and authenticated transport for a variety of services,
including remote shell access.

OpenSSH supports accessing keys provided by a PKCS#11 token.

II.  Problem Description

The ssh-agent(1) agent supports loading a PKCS#11 module from outside a
trusted whitelist.  An attacker can request loading of a PKCS#11 module
across forwarded agent-socket. [CVE-2016-10009]

When privilege separation is disabled, forwarded Unix domain sockets
would be created by sshd(8) with the privileges of 'root' instead of
the authenticated user. [CVE-2016-10010]

III. Impact

A remote attacker who have control of a forwarded agent-socket on a
remote system and have the ability to write files on the system
running ssh-agent(1) agent can run arbitrary code under the same user
credential.  Because the attacker must already have some control on
both systems, it is relatively hard to exploit this vulnerability in
a practical attack. [CVE-2016-10009]

When privilege separation is disabled (on FreeBSD, privilege separation
is enabled by default and has to be explicitly disabled), an authenticated
attacker can potentially gain root privileges on systems running OpenSSH
server. [CVE-2016-10010]

IV.  Workaround

Systems not running ssh-agent(1) and sshd(8) services are not affected.

System administrators may remove ssh-agent(1) to mitigate CVE-2016-10009.

System administrators should enable privilege separation when running
OpenSSH server, which is the FreeBSD default, to mitigate CVE-2016-10010.

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.

Kill all running ssh-agent(1) process and restart sshd(8) service.
A reboot is recommended but not required.

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

Kill all running ssh-agent(1) process and restart sshd(8) service.
A reboot is recommended but not required.

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.

# fetch https://security.FreeBSD.org/patches/SA-17:01/openssh.patch
# fetch https://security.FreeBSD.org/patches/SA-17:01/openssh.patch.asc
# gpg --verify openssh.patch.asc

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

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

c) Recompile the operating system using buildworld and installworld as
described in <URL:https://www.FreeBSD.org/handbook/makeworld.html>.

Kill all running ssh-agent(1) process and restart sshd(8) service.
A reboot is recommended but not required.

VI.  Correction details

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

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/10/                                                        r311915
releng/10.3/                                                      r311916
stable/11/                                                        r311915
releng/11.0/                                                      r311916
- -------------------------------------------------------------------------

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.openssh.com/txt/release-7.4>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-10009>

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-10010>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-17:01.openssh.asc>
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