[security bulletin] SSRT4743, SSRT4884 rev.1 - HP Tru64 UNIX TCP/IP remote Denial of Service (DoS)
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HP SECURITY BULLETIN
HPSBTU01210 REVISION: 1
SSRT4743, SSRT4884 rev.1 - HP Tru64 UNIX TCP/IP remote Denial of
Service (DoS)
NOTICE:
The information in this Security Bulletin should be acted upon
as soon as possible.
INITIAL RELEASE:
04 October 2005
POTENTIAL SECURITY IMPACT:
Remote Denial of Service (DoS)
SOURCE:
Hewlett-Packard Company
HP Software Security Response Team
VULNERABILITY SUMMARY:
Several potential security vulnerabilities have been identified
in the HP Tru64 UNIX TCP/IP including ICMP, and Initial Sequence
Number generation (ISNs). These exploits could result in a remote
Denial of Service (DoS) from network throughput reduction for
TCP connections, the reset of TCP connections, or TCP spoofing.
REFERENCES:
CERT CA-2001-09, NISCC Vulnerability Advisory VU#498440 VU#532967,
CAN-2004-0790 CAN-2004-0791 CAN-2004-1060 CAN-2001-0328
SUPPORTED SOFTWARE VERSIONS*: ONLY impacted versions are listed.
HP Tru64 UNIX 5.1B-3
HP Tru64 UNIX 5.1B-2/PK4
HP Tru64 UNIX 5.1A PK
HP Tru64 UNIX 4.0G PK4
HP Tru64 UNIX 4.0F PK8
BACKGROUND:
Special Instructions for the Customer
The Internet Control Message Protocol (ICMP) (RFC 792) is used in
the Internet Architecture to perform fault-isolation and recovery
(RFC816), which is the group of actions that hosts and routers
take to determine if a network failure has occurred.
The industry standard TCP specification (RFC 793) has a
vulnerability whereby ICMP packets can be used to perform a
variety of attacks such as blind connection reset attacks and
blind throughput-reduction attacks. Blind connection reset
attacks can be triggered by an attacker sending forged ICMP
"Destination Unreachable, host unreachable" packets or ICMP
"Destination Unreachable, port unreachable" packets. Blind
throughput-reduction attacks can be caused by an attacker sending
a forged ICMP type 4 (Source Quench) packet.
Path MTU Discovery (RFC 1191) describes a technique for
dynamically discovering the MTU (maximum transmission unit) of an
arbitrary internet path. This protocol uses ICMP packets from
the router to discover the MTU for a TCP connection path. An
attacker can reduce the throughput of a TCP connection by sending
forged ICMP packets (or their IPv6 counterpart) to the
discovering host, causing an incorrect Path MTU setting.
HP has addressed these potential vulnerabilities by providing a
new kernel tunable in Tru64 UNIX V5.1B and 5.1A,
icmp_tcpseqcheck. In Tru64 4.0F and 4.0G, HP has introduced two
new kernel tunables, icmp_tcpseqcheck and icmp_rejectcodemask.
The icmp_rejectcodemask tunable is already available in Tru64
UNIX V5.1B and 5.1A.
icmp_tcpseqcheck
The icmp_tcpseqcheck variable mitigates ICMP attacks against TCP
by checking that the TCP sequence number contained in the payload
of the ICMP error message is within the range of the data already
sent but not yet acknowledged. An ICMP error message that does
not pass this check is discarded. This behavior protects TCP
against spoofed ICMP packets.
Set the tunable as follows:
icmp_tcpseqcheck=1 (default)
Provides a level of protection that reduces the possibility
of considering a spoofed ICMP packet as valid
to one in two raised to the thirty-second power.
icmp_tcpseqcheck=0
Retains existing behavior, i.e., accepts all ICMP packets
icmp_rejectcodemask
In the Requirements for IP Version 4 Routers (RFC 1812), research
suggests that the use of ICMP Source Quench packets is an
ineffective (and unfair) antidote for congestion. Thus, HP
recommends completely ignoring ICMP Source Quench packets using
the icmp_rejectcodemask tunable. The icmp_rejectcodemask is a
bitmask that designates the ICMP codes that the system should
reject. For example, to reject ICMP Source Quench packets,
set the mask bit position for the ICMP_SOURCEQUENCH code 4,
which is two to the 4th power = 16 (0x10 hex).
The icmp_rejectcodemask tunable can be used to reject any
ICMP packet type, or multiple masks can be combined to reject
more than one type.
Note: The ICMP type codes are defined in
"/usr/include/netinet/ip_icmp.h".
Set the tunable as follows:
icmp_rejectcodemask = 0x10
Rejects ICMP Source Quench packets
icmp_rejectcodemask = 0 (default)
Retains existing behavior, i.e., accepts all ICMP packets
Adjusting the variables
The ICMP sequence check variable (icmp_tcpseqcheck) can be
adjusted using the sysconfig and sysconfigdb commands:
# sysconfig -q inet icmp_tcpseqcheck
inet:
icmp_tcpseqcheck = 1
# sysconfig -r inet icmp_tcpseqcheck=0
icmp_tcpseqcheck: reconfigured
# sysconfig -q inet icmp_tcpseqcheck
inet:
icmp_tcpseqcheck = 0
# sysconfig -q inet icmp_tcpseqcheck > /tmp/icmp_tcpseqcheck_merge
# sysconfigdb -m -f /tmp/icmp_tcpseqcheck_merge inet
# sysconfigdb -l inet
inet:
icmp_tcpseqcheck = 1
Similarly, the icmp_rejectcodemask variable can be adjusted using
the sysconfig and sysconfigdb commands:
# sysconfig -q inet icmp_rejectcodemask
inet:
icmp_rejectcodemask = 0
# sysconfig -r inet icmp_rejectcodemask=0x10
icmp_rejectcodemask: reconfigured
# sysconfig -q inet icmp_rejectcodemask
inet:
icmp_rejectcodemask = 16
# sysconfig -q inet icmp_rejectcodemask
> /tmp/icmp_rejectcodemask_merge
# sysconfigdb -m -f /tmp/icmp_rejectcodemask_merge inet
# sysconfigdb -l inet
inet:
icmp_rejectcodemask = 16
RESOLUTION:
Until the corrections are available in a mainstream
release patch kit, HP is releasing the following Early Release
Patch (ERP) kits publicly for use by any customer.
The ERP kits use dupatch to install and will not install over
any installed Customer Specific Patches (CSPs) that have file
intersections with the ERPs. Contact your service provider for
assistance if the ERP installation is blocked by any of your
installed CSPs.
The fixes contained in the ERP kits are scheduled to be
available in the following mainstream patch kits:
HP Tru64 Unix 5.1B-4
Early Release Patches
The ERPs deliver the following file:
/sys/BINARY/inet.mod
HP Tru64 UNIX 5.1B-3
ERP Kit Name: T64KIT0026447-V51BB26-ES-20050914
Kit Location:
http://www.itrc.hp.com/service/patch/patchDetail.do?
patchid=T64KIT0026447-V51BB26-ES-20050914
MD5 checksum: 168639dedac3894e6432957c178e70ba
HP Tru64 UNIX 5.1B-2/PK4
ERP Kit Name: T64KIT0026436-V51BB25-ES-20050914
Kit Location:
http://www.itrc.hp.com/service/patch/patchDetail.do?
patchid=T64KIT0026436-V51BB25-ES-20050914
MD5 checksum: ececa219e125c929d1d33bb5f2824072
HP Tru64 UNIX 5.1A PK6
ERP Kit Name: T64KIT0026446-V51AB24-ES-20050914
Kit Location:
http://www.itrc.hp.com/service/patch/patchDetail.do?
patchid=T64KIT0026446-V51AB24-ES-20050914
MD5 checksum: 75c1039c63444e530772cc2b7e25cf0a
HP Tru64 UNIX 4.0G PK4
ERP Kit Name: T64KIT0025920-V40GB22-ES-20050628
Kit Location:
http://www.itrc.hp.com/service/patch/patchDetail.do?
patchid=T64KIT0025920-V40GB22-ES-20050628
MD5 checksum: 13849fd555239d75d300d1cb46dc995f
HP Tru64 UNIX 4.0F PK8
ERP Kit Name: DUXKIT0025921-V40FB22-ES-20050628
Kit Location:
http://www.itrc.hp.com/service/patch/patchDetail.do?
patchid=DUXKIT0025921-V40FB22-ES-20050628
MD5 checksum: 743b614d39f185802701b7f2dd14ffa5
MD5 checksums are available from the ITRC patch database main
page:
http://www.itrc.hp.com/service/patch/mainPage.do
- From the patch database main page, click Tru64 UNIX,
then click verifying MD5 checksums under useful links.
General ITRC Patch Page:
http://www.itrc.hp.com/service/patch/mainPage
BULLETIN REVISION HISTORY:
Revision 0: 15 September 2005
Initial Release
Revision 1: 4 October 2005
New ERP kits are available for
HP Tru64 Unix V5.1B-3, V5.1B-2/PK4, and V5.1A PK6
SUPPORT: For further information, contact normal HP Services
support channel.
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* The Software Product Category that this Security Bulletin
relates to is represented by the 5th and 6th characters of the
Bulletin number:
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System management and security procedures must be reviewed
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to provide customers with current secure solutions.
"HP is broadly distributing this Security Bulletin in order to
bring to the attention of users of the affected HP products the
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