The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers). An example of a network attack is an attacker causing a denial of service by sending a specially crafted TCP packet across a wide area network (e.g., CVE-2004-0230).
Attack Complexity
Low
AC
The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
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
None
C
There is no impact on the confidentiality of the system; the attacker does not gain the ability to read any data.
Integrity
None
I
There is no impact on the integrity of the system; the attacker does not gain the ability to modify any files or information 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.
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
========================================================================
=====
FreeBSD-SA-06:08.sack Security Advisory
The FreeBSD Project
Topic: Infinite loop in SACK handling
Category: core
Module: netinet
Announced: 2006-02-01
Credits: Scott Wood
Affects: FreeBSD 5.3 and 5.4
Corrected: 2006-01-24 01:16:18 UTC (RELENG_5, 5.4-STABLE)
2006-02-01 19:43:10 UTC (RELENG_5_4, 5.4-RELEASE-p11)
2006-02-01 19:43:36 UTC (RELENG_5_3, 5.3-RELEASE-p26)
CVE Name: CVE-2006-0433
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
SACK (Selective Acknowledgement) is an extension to the TCP/IP protocol
that allows hosts to acknowledge the receipt of some, but not all, of
the packets sent, thereby reducing the cost of retransmissions.
II. Problem Description
When insufficient memory is available to handle an incoming selective
acknowledgement, the TCP/IP stack may enter an infinite loop.
III. Impact
By opening a TCP connection and sending a carefully crafted series of
packets, an attacker may be able to cause a denial of service.
IV. Workaround
On FreeBSD 5.4, the net.inet.tcp.sack.enable sysctl can be used to
disable the use of SACK:
# sysctl net.inet.tcp.sack.enable=0
No workaround is available for FreeBSD 5.3.
V. Solution
Perform one of the following:
1) Upgrade your vulnerable system to 5-STABLE or to the RELENG_5_4 or
RELENG_5_3 security branch dated after the correction date.
2) To patch your present system:
The following patch have been verified to apply to FreeBSD 5.3 and
5.4 systems.
a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-06:08/sack.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-06:08/sack.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_5
src/sys/netinet/tcp_sack.c 1.3.2.10
RELENG_5_4
src/UPDATING 1.342.2.24.2.20
src/sys/conf/newvers.sh 1.62.2.18.2.16
src/sys/netinet/tcp_sack.c 1.3.2.5.2.1
RELENG_5_3
src/UPDATING 1.342.2.13.2.29
src/sys/conf/newvers.sh 1.62.2.15.2.31
src/sys/netinet/tcp_sack.c 1.3.4.1
- ------------------------------------------------------------------------
-
VII. References
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-0433
The latest revision of this advisory is available at
ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-06:08.sack.
asc
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