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FreeBSD-SA-15:24.rpcbind                                    Security Advisory
                                                          The FreeBSD Project

Topic:          rpcbind(8) remote denial of service [REVISED]

Category:       core
Module:         rpcbind
Announced:      2015-09-29, revised on 2015-10-02
Affects:        All supported versions of FreeBSD.
Corrected:      2015-10-02 16:36:16 UTC (stable/10, 10.2-STABLE)
                2015-10-02 16:37:06 UTC (releng/10.2, 10.2-RELEASE-p5)
                2015-10-02 16:37:06 UTC (releng/10.1, 10.1-RELEASE-p22)
                2015-10-02 16:36:16 UTC (stable/9, 9.3-STABLE)
                2015-10-02 16:37:06 UTC (releng/9.3, 9.3-RELEASE-p28)
CVE Name:       CVE-2015-7236

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/>.

0.   Revision history

v1.0  2015-09-29 Initial release.
v1.1  2015-10-02 Revised patch to address a regression related to NIS usage

I.   Background

Sun RPC is a remote procedure call framework which allows clients to invoke
procedures in a server process over a network transparently.

The rpcbind(8) utility is a server that converts RPC program numbers into
universal addresses.  It must be running on the host to be able to make RPC
calls on a server on that machine.

The Sun RPC framework uses a netbuf structure to represent the transport
specific form of a universal transport address.  The structure is expected
to be opaque to consumers.  In the current implementation, the structure
contains a pointer to a buffer that holds the actual address.

II.  Problem Description

In rpcbind(8), netbuf structures are copied directly, which would result in
two netbuf structures that reference to one shared address buffer.  When one
of the two netbuf structures is freed, access to the other netbuf structure
would result in an undefined result that may crash the rpcbind(8) daemon.

III. Impact

A remote attacker who can send specifically crafted packets to the rpcbind(8)
daemon can cause it to crash, resulting in a denial of service condition.

IV.  Workaround

No workaround is available, but systems that do not provide the rpcbind(8)
service to untrusted systems, or do not provide any RPC services are not
vulnerable.  On FreeBSD, typical RPC based services includes NIS and NFS.

Alternatively, rpcbind(8) can be configured to bind on specific IP
address(es) by using the '-h' option.  This may be used to reduce the attack
vector when the system has multiple network interfaces and when some of them
would face an untrusted network.

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.

Restart the applicable daemons, or reboot the system.  Because rpcbind(8)
is an essential service to all RPC service daemons, these daemons may also
need to be restarted.

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

Restart the applicable daemons, or reboot the system.  Because rpcbind(8)
is an essential service to all RPC service daemons, these daemons may also
need to be restarted.

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-15:24/rpcbind.patch
# fetch https://security.FreeBSD.org/patches/SA-15:24/rpcbind.patch.asc
# gpg --verify rpcbind.patch.asc

# fetch https://security.FreeBSD.org/patches/SA-15:24/rpcbind-00.patch
# fetch https://security.FreeBSD.org/patches/SA-15:24/rpcbind-00.patch.asc
# gpg --verify rpcbind-00.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 the applicable daemons, or reboot the system.

VI.  Correction details

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

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/9/                                                         r288511
releng/9.3/                                                       r288512
stable/10/                                                        r288511
releng/10.1/                                                      r288512
releng/10.2/                                                      r288512
- -------------------------------------------------------------------------

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-2015-7236>

<URL:https://bugzilla.suse.com/show_bug.cgi?id=946204>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-15:24.rpcbind.asc>
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