FreeBSD Security Advisories
2006-Mar-01 07:03 UTC
FreeBSD Security Advisory FreeBSD-SA-06:10.nfs
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============================================================================FreeBSD-SA-06:10.nfs
Security Advisory
The FreeBSD Project
Topic: Remote denial of service in NFS server
Category: core
Module: sys_nfsserver
Announced: 2006-03-01
Credits: Evgeny Legerov
Affects: All FreeBSD releases.
Corrected: 2006-03-01 14:18:11 UTC (RELENG_6, 6.1-PRERELEASE)
2006-03-01 14:18:46 UTC (RELENG_6_0, 6.0-RELEASE-p5)
2006-03-01 14:19:48 UTC (RELENG_5, 5.5-PRERELEASE)
2006-03-01 14:21:01 UTC (RELENG_5_4, 5.4-RELEASE-p12)
2006-03-01 14:24:52 UTC (RELENG_5_3, 5.3-RELEASE-p27)
2006-03-01 14:21:56 UTC (RELENG_4, 4.11-STABLE)
2006-03-01 14:22:30 UTC (RELENG_4_11, 4.11-RELEASE-p15)
2006-03-01 14:23:07 UTC (RELENG_4_10, 4.10-RELEASE-p21)
CVE Name: CVE-2006-0900
For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit
<URL:http://www.freebsd.org/security/>.
I. Background
The Network File System (NFS) allows a host to export some or all of
its filesystems so that other hosts can access them over the network
and mount them as if they were on local disks. NFS is built on top of
the Sun Remote Procedure Call (RPC) framework.
II. Problem Description
A part of the NFS server code charged with handling incoming RPC
messages via TCP had an error which, when the server received a
message with a zero-length payload, would cause a NULL pointer
dereference which results in a kernel panic. The kernel will only
process the RPC messages if a userland nfsd daemon is running.
III. Impact
The NULL pointer deference allows a remote attacker capable of sending
RPC messages to an affected FreeBSD system to crash the FreeBSD system.
IV. Workaround
1) Disable the NFS server: set the nfs_server_enable variable to "NO"
in /etc/rc.conf, and reboot.
Alternatively, if there are no active NFS clients (as listed by the
showmount(8) utility), simply killing the mountd and nfsd processes
should suffice.
2) Add firewall rules to block RPC traffic to the NFS server from
untrusted hosts.
V. Solution
Perform one of the following:
1) Upgrade your vulnerable system to 4-STABLE, 5-STABLE, or 6-STABLE,
or to the RELENG_6_0, RELENG_5_4, RELENG_5_3, RELENG_4_11, or
RELENG_4_10 security branch dated after the correction date.
2) To patch your present system:
The following patches have been verified to apply to FreeBSD 4.10,
4.11, 5.3, 5.4, and 6.0 systems.
a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.
[FreeBSD 4.x]
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-06:10/nfs4.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-06:10/nfs4.patch.asc
[FreeBSD 5.x and 6.x]
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-06:10/nfs.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-06:10/nfs.patch.asc
b) Apply the patch.
# cd /usr/src
# patch < /path/to/patch
c) Recompile your kernel as described in
<URL:http://www.freebsd.org/handbook/kernelconfig.html> and reboot the
system.
VI. Correction details
The following list contains the revision numbers of each file that was
corrected in FreeBSD.
Branch Revision
Path
- -------------------------------------------------------------------------
RELENG_4
src/sys/nfs/nfs_socket.c 1.60.2.7
RELENG_4_11
src/UPDATING 1.73.2.91.2.16
src/sys/conf/newvers.sh 1.44.2.39.2.19
src/sys/nfs/nfs_socket.c 1.60.2.6.6.1
RELENG_4_10
src/UPDATING 1.73.2.90.2.22
src/sys/conf/newvers.sh 1.44.2.34.2.23
src/sys/nfs/nfs_socket.c 1.60.2.6.4.1
RELENG_5
src/sys/nfsserver/nfs_srvsock.c 1.92.2.2
RELENG_5_4
src/UPDATING 1.342.2.24.2.21
src/sys/conf/newvers.sh 1.62.2.18.2.17
src/sys/nfsserver/nfs_srvsock.c 1.92.2.1.2.1
RELENG_5_3
src/UPDATING 1.342.2.13.2.30
src/sys/conf/newvers.sh 1.62.2.15.2.32
src/sys/nfsserver/nfs_srvsock.c 1.92.4.1
RELENG_6
src/sys/nfsserver/nfs_srvsock.c 1.94.2.1
RELENG_6_0
src/UPDATING 1.416.2.3.2.10
src/sys/conf/newvers.sh 1.69.2.8.2.6
src/sys/nfsserver/nfs_srvsock.c 1.94.4.1
- -------------------------------------------------------------------------
VII. References
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-0900
The latest revision of this advisory is available at
ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-06:10.nfs.asc
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FreeBSD Security Advisories wrote:> Topic: Remote denial of service in NFS server > [...] > IV. Workaround > > 1) Disable the NFS server: set the nfs_server_enable variable to "NO" > in /etc/rc.conf, and reboot. > > Alternatively, if there are no active NFS clients (as listed by the > showmount(8) utility), simply killing the mountd and nfsd processes > should suffice. > > 2) Add firewall rules to block RPC traffic to the NFS server from > untrusted hosts.There's one more workaround: Since this problem only affects RPC messages incoming via TCP, disabling the use of TCP with NFS will correct this while still allowing NFS to run over UDP. To disable use of TCP for NFS, remove the "-t" flag from nfs_server_flags in /etc/rc.conf and reboot. Colin Percival