The vulnerable system is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either: the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or through terminal emulation (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., using social engineering techniques to trick a legitimate user into opening a malicious document).
Privileges Required
None
PR
The attacker is unauthenticated prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction
None
UI
The vulnerable system can be exploited without interaction from any human user, other than the attacker. Examples include: a remote attacker is able to send packets to a target system a locally authenticated attacker executes code to elevate privileges
Scope
Unchanged
S
An exploited vulnerability can only affect resources managed by the same security authority. In the case of a vulnerability in a virtualized environment, an exploited vulnerability in one guest instance would not affect neighboring guest instances.
Confidentiality
High
C
There is total information disclosure, resulting in all data on the system being revealed to the attacker, or there is a possibility of the attacker gaining control over confidential data.
Integrity
High
I
There is a total compromise of system integrity. There is a complete loss of system protection, resulting in the attacker being able to modify any file on the target system.
Availability
High
A
There is a total shutdown of the affected resource. The attacker can deny access to the system or data, potentially causing significant loss to the organization.
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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.a
sc
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