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FreeBSD Security Advisory - FreeBSD-SA-16:07.openssh

FreeBSD Security Advisory - FreeBSD-SA-16:07.openssh
Posted Jan 15, 2016
Authored by Qualys Security Advisory Team | Site security.freebsd.org

FreeBSD Security Advisory - The OpenSSH client code contains experimental support for resuming SSH connections (roaming). The matching server code has never been shipped, but the client code was enabled by default and could be tricked by a malicious server into leaking client memory to the server, including private client user keys. A user that authenticates to a malicious or compromised server may reveal private data, including the private SSH key of the user.

tags | advisory
systems | freebsd
advisories | CVE-2016-0777
MD5 | db88bcb6e48b14664b5ad70f4388c83d

FreeBSD Security Advisory - FreeBSD-SA-16:07.openssh

Change Mirror Download
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=============================================================================
FreeBSD-SA-16:07.openssh Security Advisory
The FreeBSD Project

Topic: OpenSSH client information leak

Category: contrib
Module: openssh
Announced: 2016-01-14
Credits: Qualys Security Advisory Team
Affects: All supported versions of FreeBSD.
Corrected: 2016-01-14 22:42:43 UTC (stable/10, 10.2-STABLE)
2016-01-14 22:45:33 UTC (releng/10.2, 10.2-RELEASE-p10)
2016-01-14 22:47:54 UTC (releng/10.1, 10.1-RELEASE-p27)
2016-01-14 22:50:35 UTC (stable/9, 9.3-STABLE)
2016-01-14 22:53:07 UTC (releng/9.3, 9.3-RELEASE-p34)
CVE Name: CVE-2016-0777

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. The ssh(1) is client side utility used
to login to remote servers.

II. Problem Description

The OpenSSH client code contains experimental support for resuming SSH
connections (roaming). The matching server code has never been shipped, but
the client code was enabled by default and could be tricked by a malicious
server into leaking client memory to the server, including private client
user keys.

III. Impact

A user that authenticates to a malicious or compromised server may reveal
private data, including the private SSH key of the user.

IV. Workaround

The vulnerable code in the client can be completely disabled by adding
'UseRoaming no' to the global ssh_config(5) file, or to user configuration
in ~/.ssh/config, or by passing -oUseRoaming=no on the command line.

All current remote ssh(1) sessions need to be restared after changing
the configuration file.

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.

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

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-16:07/openssh.patch
# fetch https://security.FreeBSD.org/patches/SA-16:07/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>.

VI. Correction details

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

Branch/path Revision
- -------------------------------------------------------------------------
stable/9/ r294053
releng/9.3/ r294054
stable/10/ r294049
releng/10.1/ r294051
releng/10.2/ r294052
- -------------------------------------------------------------------------

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-2016-0777>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-16:07.openssh.asc>
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