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HistoryDec 24, 2004 - 12:00 a.m.

[Security Bulletin] SSRT4696 rev.0 - HP Tru64 UNIX TCP Stack Remote Denial of Service (DoS)


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SSRT4696 rev.0 - HP Tru64 UNIX TCP Stack
Remote Denial of Service (DoS)

There are no restrictions for distribution of this Bulletin
provided that it remains complete and intact.

The information in this Security bulletin should be acted upon
as soon as possible.

22 December 2004

Remote Denial of Service (DoS)

HP Software Security Response Team

NISCC Advisory 236929, CVE CAN-2004-0230

A potential security vulnerability has been identified in the
Transmission Control Protocol (TCP) on HP Tru64 UNIX systems.
The potential vulnerability could be remotely exploitable,
resulting in denial of service (DoS).

SUPPORTED SOFTWARE VERSIONS*: ONLY impacted versions are listed.
HP Tru64 UNIX V5.1B PK4
HP Tru64 UNIX V5.1B PK3
HP Tru64 UNIX V5.1A PK6
HP Tru64 UNIX V4.0G PK4
HP Tru64 UNIX V4.0F PK8

Special Instructions:

The industry standard TCP specification (RFC793) has a
vulnerability whereby established TCP connections can be
reset by an attacker.

TCP sessions, including Telnet, SSH, SFTP and HTTP may be
disconnected without warning. TCP sessions that have been
disconnected can be re-established.

HP Tru64 UNIX has addressed this potential vulnerability, called
a TCP reset attack, by providing a new kernel tunable variable,
tcp_rst_win (TCP reset window).

The tcp_rst_win variable mitigates the TCP reset attack by
reducing the window size in which a TCP reset packet will be
accepted by the Tru64 system.

Set the tunable as follows:

tcp_rst_win = -1 (default)

Retains existing TCP behavior.

tcp_rst_win = 2048

Provides a level of protection which will significantly reduce
the size of the TCP reset window while allowing for common TCP
client/server sequence number variations. This will allow a
reset packet to be accepted by the Tru64 system when the remote
machine has unacknowledged outstanding packets of up to a total
of 2048 bytes.

tcp_rst_win = 0

Provides maximum security against the potential DoS condition.

Setting tcp_rst_win to "0" provides the highest level of
protection without migrating to an IPSec environment. This
setting restricts the acceptance of a reset packet to the
current sequence number and may result in the rejection of
valid reset packets where sent data packets have not been

Customers who are extremely sensitive to this security threat
should implement IPSec, available in HP Tru64 UNIX 5.1A and
5.1B. Tru64 UNIX V4.0F and V4.0G can receive maximum available
protection with tcp_rst_win to "0".

The TCP reset window variable (tcp_rst_win) may be adjusted
using the "sysconfig" and "sysconfigdb" commands:

sysconfig -q inet tcp_rst_win

tcp_rst_win = -1

sysconfig -r inet tcp_rst_win=2048

tcp_rst_win: reconfigured

sysconfig -q inet tcp_rst_win

tcp_rst_win = 2048

sysconfig -q inet tcp_rst_win > /tmp/tcp_rst_win_merge

sysconfigdb -m -f /tmp/tcp_rst_win_merge inet

sysconfigdb -l inet

tcp_rst_win = 2048

The fixes contained in the ERP kits are scheduled to be
available in the following mainstream patch kits:

HP Tru64 UNIX V5.1B PK 5
HP Tru64 UNIX V5.1A PK 7

Until the corrections are available in mainstream release
patch kits, 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 installation of the ERPs is blocked by
any of your installed CSPs.

HP Tru64 UNIX 5.1B-2/PK4
ERP Kit Name: T64KIT0024531-V51BB25-ES-20041219
General ITRC Patch Page:
Kit Location:

HP Tru64 UNIX 5.1B-1/PK3
ERP Kit Name: T64KIT0024529-V51BB24-ES-20041219
General ITRC Patch Page:
Kit Location:

HP Tru64 UNIX 5.1A
PREREQUISITE: HP Tru64 UNIX with 5.1A with PK6 installed
ERP Kit Name: T64KIT0024527-V51AB24-ES-20041219
General ITRC Patch Page:
Kit Location:

HP Tru64 UNIX 4.0G
PREREQUISITE: HP Tru64 UNIX with 4.0G with PK4 installed
ERP Kit Name: T64KIT0024524-V40GB22-ES-20041219
General ITRC Patch Page:
Kit Location:

HP Tru64 UNIX 4.0F
PREREQUISITE: HP Tru64 UNIX with 4.0F with PK8 (BL22) installed
ERP Kit Name: DUXKIT0024523-V40FB22-ES-20041219
General ITRC Patch Page:
Kit Location:

Revision 0 - 22 December 2004
Initial Release

  • The software product category that this Security Bulletin
    relates to is represented by the 5th and 6th characters of the
    Bulletin number: GN=General, MA=Management Agents,
    MI=Misc. 3rd party, MP=HP-MPE/iX, NS=HP NonStop Servers,
    OV=HP OpenVMS, PI=HP Printing & Imaging, ST=HP Storage,
    TU=HP Tru64 UNIX, TL=Trusted Linux, UX=HP-UX, VV=Virtual Vault

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REPORT: To report a potential security vulnerability with any HP
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System management and security procedures must be reviewed
frequently to maintain system integrity. HP is continually
reviewing and enhancing the security features of software products
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
important security information contained in this Bulletin. HP
recommends that all users determine the applicability of this
information to their individual situations and take appropriate
action. HP does not warrant that this information is necessarily
accurate or complete for all user situations and, consequently,
HP will not be responsible for any damages resulting from user's
use or disregard of the information provided in this Bulletin.
To the extent permitted by law, HP disclaims all warranties,
either express or implied, including the warranties of
merchantability and fitness for a particular purpose, title
and non-infringement."

(c)Copyright 2004 Hewlett-Packard Development Company, L.P.
Hewlett-Packard Company shall not be liable for technical or
editorial errors or omissions contained herein. The information
provided is provided "as is" without warranty of any kind. To the
extent permitted by law, neither HP or its affiliates,
subcontractors or suppliers will be liable for incidental, special
or consequential damages including downtime cost; lost profits;
damages relating to the procurement of substitute products or
services; or damages for loss of data, or software restoration.
The information in this document is subject to change without
notice. Hewlett-Packard Company and the names of Hewlett-Packard
products referenced herein are trademarks of Hewlett-Packard
Company in the United States and other countries. Other product
and company names mentioned herein may be trademarks of their
respective owners.

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