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FreeBSD-SA-16:29.bspatch Security Advisory
The FreeBSD Project

Topic: Heap overflow vulnerability in bspatch

Category: core
Module: bsdiff
Announced: 2016-10-10
Affects: All supported versions of FreeBSD.
2016-09-22 21:05:21 UTC (stable/11, 11.0-STABLE)
2016-09-27 19:36:12 UTC (releng/11.0, 11.0-RELEASE-p1)
2016-09-22 21:16:54 UTC (stable/10, 10.3-STABLE)
2016-10-10 07:18:54 UTC (releng/10.3, 10.3-RELEASE-p10)
2016-10-10 07:18:54 UTC (releng/10.2, 10.2-RELEASE-p23)
2016-10-10 07:18:54 UTC (releng/10.1, 10.1-RELEASE-p40)
2016-09-23 01:52:06 UTC (stable/9, 9.3-STABLE)
2016-10-10 07:19:16 UTC (releng/9.3, 9.3-RELEASE-p48)

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 bspatch utility generates newfile from oldfile and patchfile where
patchfile is a binary patch built by bsdiff(1).

II. Problem Description

The implementation of bspatch is susceptible to integer overflows with
carefully crafted input, potentially allowing an attacker who can control
the patch file to write at arbitrary locations in the heap. This issue
was partially addressed in FreeBSD-SA-16:25.bspatch, but some possible
integer overflows remained.

III. Impact

An attacker who can control the patch file can cause a crash or run arbitrary
code under the credentials of the user who runs bspatch, in many cases, root.

IV. Workaround

No workaround is available.

V. Solution

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

No reboot is needed.

Perform one of the following:

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.

Because this vulnerability exists in bspatch, a component used by
freebsd-update, a special procedure must be followed to safely update.
First, truncate bspatch to a zero byte file:

# :> /usr/bin/bspatch

FreeBSD-update will fall back to replacing bspatch, rather than applying
a binary patch. Proceed with FreeBSD-update as usual:

# freebsd-update fetch
# freebsd-update install

No reboot is needed.

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-16:29/bspatch.patch
# fetch https://security.FreeBSD.org/patches/SA-16:29/bspatch.patch.asc
# gpg –verify bspatch.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/ r306222
releng/9.3/ r306942
stable/10/ r306215
releng/10.1/ r306941
releng/10.2/ r306941
releng/10.3/ r306941
stable/11/ r306213
releng/11.0/ r306379
– ————————————————————————-

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://gist.github.com/anonymous/e48209b03f1dd9625a992717e7b89c4f>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-16:29.bspatch.asc>
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