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FreeBSD-SA-15:20.expat Security Advisory
The FreeBSD Project

Topic: Multiple integer overflows in expat (libbsdxml) XML parser

Category: contrib
Module: libbsdxml
Announced: 2015-08-18
Affects: All supported versions of FreeBSD.
Corrected: 2015-08-18 19:30:05 UTC (stable/10, 10.2-STABLE)
2015-08-18 19:30:35 UTC (releng/10.1, 10.1-RELEASE-p18)
2015-08-18 19:30:17 UTC (releng/10.2, 10.2-RC3-p1)
2015-08-18 19:30:17 UTC (releng/10.2, 10.2-RELEASE-p1)
2015-08-18 19:30:05 UTC (stable/9, 9.3-STABLE)
2015-08-18 19:30:35 UTC (releng/9.3, 9.3-RELEASE-p23)
CVE Name: CVE-2015-1283

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

Expat is an XML parser library written in C. It is a stream-oriented
parser in which an application registers handlers for things the parser
might find in the XML document (like start tags).

The FreeBSD base system ships libexpat as libbsdxml for components that
need to parse XML data. Some of these applications use the XML parser
on trusted data from the kernel, for instance the geom(8) configuration
utilities, while other applications, like tar(1), cpio(1), svnlite(1)
and unbound-anchor(8), may use the XML parser on input from network or
the user.

II. Problem Description

Multiple integer overflows have been discovered in the XML_GetBuffer()
function in the expat library.

III. Impact

The integer overflows may be exploited by using specifically crafted XML
data and lead to infinite loop, or a heap buffer overflow, which results
in a Denial of Service condition, or enables remote attackers to execute
arbitrary code.

IV. Workaround

No workaround is available, but the problem is only exploitable when the
affected system needs to process data from an untrusted source.

Because the library is used by many third party applications, we advise
system administrators to check and make sure that they have the latest
expat version as well, and restart all third party services, or reboot
the system.

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.

A reboot is not required after updating the base system.

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

A reboot is not required after updating the base system.

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-15:20/expat.patch
# fetch https://security.FreeBSD.org/patches/SA-15:20/expat.patch.asc
# gpg –verify expat.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>.

The FreeBSD base system do not install daemons that uses the library,
therefore, a reboot is not required after updating the base system.

VI. Correction details

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

Branch/path Revision
– ————————————————————————-
stable/9/ r286900
releng/9.3/ r286902
stable/10/ r286900
releng/10.1/ r286902
releng/10.2/ r286901
– ————————————————————————-

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-2015-1283>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-15:20.expat.asc>
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