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FreeBSD-SA-16:06.bsnmpd Security Advisory
The FreeBSD Project

Topic: Insecure default bsnmpd.conf permissions

Category: contrib
Module: bsnmpd
Announced: 2016-01-14
Credits: Pierre Kim
Affects: All supported versions of FreeBSD.
Corrected: 2016-01-14 09:11:42 UTC (stable/10, 10.2-STABLE)
2016-01-14 09:10:46 UTC (releng/10.2, 10.2-RELEASE-p9)
2016-01-14 09:11:16 UTC (releng/10.1, 10.1-RELEASE-p26)
2016-01-14 09:11:48 UTC (stable/9, 9.3-STABLE)
2016-01-14 09:11:26 UTC (releng/9.3, 9.3-RELEASE-p33)
CVE Name: CVE-2015-5677

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 bsnmpd daemon serves the Internet SNMP (Simple Network Management
Protocol). It is intended to serve only the absolute basic MIBs and
implements all other MIBs through loadable modules.

II. Problem Description

The SNMP protocol supports an authentication model called USM, which relies
on a shared secret. The default permission of the bsnmpd configuration file,
/etc/bsnmpd.conf, is weak and does not provide adequate protection against
local unprivileged users.

III. Impact

A local user may be able to read the shared secret, if configured and used
by the system administrator.

IV. Workaround

No workaround is available, but systems that do not use bsnmpd with its USM
authentication model are not vulnerable.

V. Solution

This vulnerability can be fixed by modifying the permission on
/etc/bsnmpd.conf to owner root:wheel and permission 0600.

The patch is provided mainly for third party vendors who deploy FreeBSD
and provide a safe default. The patch itself DOES NOT fix the permissions
for existing installations.

The patch can be applied by performing one of the following:

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

The system administrator should change the permission on /etc/bsnmpd.conf
to root:wheel and 0600.

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

The system administrator should change the permission on /etc/bsnmpd.conf
to root:wheel and 0600.

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-16:06/bsnmpd.patch
# fetch https://security.FreeBSD.org/patches/SA-16:06/bsnmpd.patch.asc
# gpg –verify bsnmpd.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/ r293898
releng/9.3/ r293896
stable/10/ r293897
releng/10.1/ r293894
releng/10.2/ r293893
– ————————————————————————-

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-2015-5677>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-16:06.bsnmpd.asc>
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