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FreeBSD-SA-19:20.bsnmp                                      Security Advisory
                                                          The FreeBSD Project

Topic:          Insufficient message length validation in bsnmp library

Category:       contrib
Module:         bsnmp
Announced:      2019-08-06
Credits:        Guido Vranken <guidovranken@gmail.com>
Affects:        All supported versions of FreeBSD.
Corrected:      2019-08-06 16:11:16 UTC (stable/12, 12.0-STABLE)
                2019-08-06 17:12:17 UTC (releng/12.0, 12.0-RELEASE-p9)
                2019-08-06 16:12:43 UTC (stable/11, 11.3-STABLE)
                2019-08-06 17:12:17 UTC (releng/11.3, 11.3-RELEASE-p2)
                2019-08-06 17:12:17 UTC (releng/11.2, 11.2-RELEASE-p13)
CVE Name:       CVE-2019-5610

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 bsnmp software library is used for the Internet SNMP (Simple Network
Management Protocol).  As part of this it includes functions to handle ASN.1
(Abstract Syntax Notation One).

II.  Problem Description

A function extracting the length from type-length-value encoding is not
properly validating the submitted length.

III. Impact

A remote user could cause, for example, an out-of-bounds read, decoding of
unrelated data, or trigger a crash of the software such as bsnmpd resulting
in a denial of service.

IV.  Workaround

No workaround is available.

V.   Solution

Perform one of the following:

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

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

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-19:20/bsnmp.patch
# fetch https://security.FreeBSD.org/patches/SA-19:20/bsnmp.patch.asc
# gpg --verify bsnmp.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>.

Restart all daemons that use the library, or reboot the system.

VI.  Correction details

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

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/12/                                                        r350637
releng/12.0/                                                      r350646
stable/11/                                                        r350638
releng/11.3/                                                      r350646
releng/11.2/                                                      r350646
- -------------------------------------------------------------------------

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-2019-5610>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-19:20.bsnmp.asc>
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