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Home » Hacking News » SGI-19950123-02-I-IRIX TCP/IP Initial Sequence Numbers

SGI-19950123-02-I-IRIX TCP/IP Initial Sequence Numbers

by Nikola Strahija on March 21st, 2002 As part of on going security efforts, SGI acknowledges the "statistical weaknesses in TCP/IP initial sequence numbers" vulnerability issue and is investigating.

This was reported by Tim Newsham of Guardent and CERT:

No further information is available at this time.

For the protection of all our customers, SGI does not disclose, discuss
or confirm vulnerabilities until a full investigation has occurred and
any necessary fixes are available for all vulnerable and supported IRIX
operating systems.

Until SGI has more definitive information to provide, customers are
encouraged to assume all security vulnerabilities as exploitable and take
appropriate steps according to local site security policies and requirements.

As further information becomes available, additional advisories will be
issued via the normal SGI security information distribution methods
including the wiretap mailing list.

- --------------------------
- --- Temporary Solution ---
- --------------------------

SGI has been tracking TCP ISN randomization issues over the years.
For details please see the following security advisories:
SGI Advisory 19950123-02-I

CERT CA-1996-21

SGI Advisory 19961202-01-PX

CERT CA-1995-01

Thus far, SGI has implemented RFC 1948 with MD5 on IRIX 6.5.3 and
above using the tcpiss_md5 tunable kernel parameter. The default is

To enable the tcpiss_md5 kernel parameter, perform the following
command as root:

# /usr/sbin/systune -b tcpiss_md5 1

To verify RFC 1948 has been enabled in IRIX, use the following command
as root:

# /usr/sbin/systune tcpiss_md5

This should return:

tcpiss_md5 = 1 (0x1)

SGI is investigating if more work in this area is needed beyond setting
tcpiss_md5=1 to fully address all issues presented in the CERT advisory.

- -------------------
- --- Information ---
- -------------------

SGI Security Advisories can be found at: and

SGI Security Patches can be found at: and

SGI patches for IRIX can be found at the following patch servers: and

SGI freeware updates for IRIX can be found at:

SGI fixes for SGI open sourced code can be found on:

SGI patches and RPMs for Linux can be found at: or

SGI patches for Windows NT or 2000 can be found at:

IRIX 5.2-6.4 Recommended/Required Patch Sets can be found at: and

IRIX 6.5 Maintenance Release Streams can be found at:

IRIX 6.5 Software Update CDs can be obtained from:

The primary SGI anonymous FTP site for security advisories and patches is ( Security advisories and patches are
located under the URL

For security and patch management reasons, (mirrors security FTP repository) lags behind and does not do a
real-time update.

- ------------------------
- --- Acknowledgments ----
- ------------------------

SGI wishes to thank Tim Newsham, Guardent, CERT, and the members of
the Internet Community at large for their assistance in this matter.

- -----------------------------------------
- --- SGI Security Information/Contacts ---
- -----------------------------------------

If there are questions about this document, email can be sent to
[email protected]


SGI provides security information and patches for use by the entire SGI
community. This information is freely available to any person needing the
information and is available via anonymous FTP and the Web.

The primary SGI anonymous FTP site for security advisories and patches is ( Security advisories and patches are
located under the URL

The SGI Security Headquarters Web page is accessible at the URL:

For issues with the patches on the FTP sites, email can be sent to
[email protected]

For assistance obtaining or working with security patches, please
contact your SGI support provider.


SGI provides a free security mailing list service called wiretap and
encourages interested parties to self-subscribe to receive (via email) all
SGI Security Advisories when they are released. Subscribing to the mailing
list can be done via the Web
( or by sending email to
SGI as outlined below.

% mail [email protected]
subscribe wiretap

In the example above, is the email address that you wish
the mailing list information sent to. The word end must be on a separate
line to indicate the end of the body of the message. The control-d (^d) is
used to indicate to the mail program that you are finished composing the
mail message.


SGI provides a comprehensive customer World Wide Web site. This site is
located at .


If there are general security questions on SGI systems, email can be sent to
[email protected]

For reporting *NEW* SGI security issues, email can be sent to
[email protected] or contact your SGI support provider. A support
contract is not required for submitting a security report.

This information is provided freely to all interested parties
and may be redistributed provided that it is not altered in any
way, SGI is appropriately credited and the document retains and
includes its valid PGP signature.

Version: 2.6.2


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