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FreeBSD Security Advisory - mountd ACL Mishandling

FreeBSD Security Advisory - mountd ACL Mishandling
Posted Apr 21, 2011
Site security.freebsd.org

FreeBSD Security Advisory - The mountd(8) daemon services NFS mount requests from other client machines. When mountd is started, it loads the export host addresses and options into the kernel using the mount(2) system call. While parsing the exports(5) table, a network mask in the form of "-network=netname/prefixlength" results in an incorrect network mask being computed if the prefix length is not a multiple of 8. For example, specifying the ACL for an export as "-network 192.0.2.0/23" would result in a netmask of 255.255.127.0 being used instead of the correct netmask of 255.255.254.0.

tags | advisory, kernel
systems | freebsd
advisories | CVE-2011-1739
SHA-256 | daab8415751957e3ad1463b8ec1447aa42b593613cb89eb97366e0b6b20911e2

FreeBSD Security Advisory - mountd ACL Mishandling

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=============================================================================
FreeBSD-SA-11:01.mountd Security Advisory
The FreeBSD Project

Topic: Network ACL mishandling in mountd(8)

Category: core
Module: mountd
Announced: 2011-04-20
Credits: Ruslan Ermilov
Affects: All supported versions of FreeBSD
Corrected: 2011-04-20 21:00:24 UTC (RELENG_7, 7.4-STABLE)
2011-04-20 21:00:24 UTC (RELENG_7_3, 7.3-RELEASE-p5)
2011-04-20 21:00:24 UTC (RELENG_7_4, 7.4-RELEASE-p1)
2011-04-20 21:00:24 UTC (RELENG_8, 8.2-STABLE)
2011-04-20 21:00:24 UTC (RELENG_8_1, 8.1-RELEASE-p3)
2011-04-20 21:00:24 UTC (RELENG_8_2, 8.2-RELEASE-p1)
CVE Name: CVE-2011-1739

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:http://security.FreeBSD.org/>.

I. Background

The mountd(8) daemon services NFS mount requests from other client
machines. When mountd is started, it loads the export host addresses
and options into the kernel using the mount(2) system call.

II. Problem Description

While parsing the exports(5) table, a network mask in the form of
"-network=netname/prefixlength" results in an incorrect network mask
being computed if the prefix length is not a multiple of 8.

For example, specifying the ACL for an export as "-network 192.0.2.0/23"
would result in a netmask of 255.255.127.0 being used instead of the
correct netmask of 255.255.254.0.

III. Impact

When using a prefix length which is not multiple of 8, access would be
granted to the wrong client systems.

IV. Workaround

For IPv4-only systems, using the -netmask option instead of CIDR notion
for -network circumvents this bug.

A firewall such as pf(4) can (and probably should) be used to restrict
access to the NFS server.

Systems not providing NFS service, or using a prefix length which is a
multiple of 8 in all ACLs, are not affected.

V. Solution

Perform one of the following:

1) Upgrade your vulnerable system to 7-STABLE or 8-STABLE, or to the
RELENG_8_2, RELENG_8_1, RELENG_7_4, RELENG_7_3 security branch dated
after the correction date.

2) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to FreeBSD 7.3, 7.4,
8.1 and 8.2 systems.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch http://security.FreeBSD.org/patches/SA-11:01/mountd.patch
# fetch http://security.FreeBSD.org/patches/SA-11:01/mountd.patch.asc

b) Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch
# cd /usr/src/usr.sbin/mountd
# make obj && make depend && make && make install

3) To update your vulnerable system via a binary patch:

Systems running 7.3-RELEASE, 7.4-RELEASE, 8.1-RELEASE or 8.2-RELEASE on
the i386 or amd64 platforms can be updated via the freebsd-update(8)
utility:

# freebsd-update fetch
# freebsd-update install

VI. Correction details

The following list contains the revision numbers of each file that was
corrected in FreeBSD.

CVS:

Branch Revision
Path
- -------------------------------------------------------------------------
RELENG_7
src/usr.sbin/mountd/mountd.c 1.94.2.3
RELENG_7_4
src/UPDATING 1.507.2.36.2.3
src/sys/conf/newvers.sh 1.72.2.18.2.6
src/usr.sbin/mountd/mountd.c 1.94.2.2.8.2
RELENG_7_3
src/UPDATING 1.507.2.34.2.7
src/sys/conf/newvers.sh 1.72.2.16.2.9
src/usr.sbin/mountd/mountd.c 1.94.2.2.6.2
RELENG_8
src/usr.sbin/mountd/mountd.c 1.105.2.3
RELENG_8_2
src/UPDATING 1.632.2.19.2.3
src/sys/conf/newvers.sh 1.83.2.12.2.6
src/usr.sbin/mountd/mountd.c 1.105.2.2.4.2
RELENG_8_1
src/UPDATING 1.632.2.14.2.6
src/sys/conf/newvers.sh 1.83.2.10.2.7
src/usr.sbin/mountd/mountd.c 1.105.2.2.2.2
- -------------------------------------------------------------------------

Subversion:

Branch/path Revision
- -------------------------------------------------------------------------
stable/7/ r220901
releng/7.3/ r220901
releng/7.4/ r220901
stable/8/ r220901
releng/8.1/ r220901
releng/8.2/ r220901
- -------------------------------------------------------------------------

VII. References

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2011-1739

The latest revision of this advisory is available at
http://security.FreeBSD.org/advisories/FreeBSD-SA-11:01.mountd.asc
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