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Ultrix DECnet Internet Gateway

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             The Computer Incident Advisory Capability
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                         Information Bulletin

	Vulnerability in ULTRIX DECnet-Internet Gateway Software

September 26, 1991, 1300 PDT	                            Number B-43
PROBLEM:   The ULTRIX DECNet-Internet Gateway software can be exploited
	   to obtain root privilege on ULTRIX Gateway machines.
PLATFORM:  ULTRIX Version 4.0, 4.1, and 4.2, both RISC and VAX
DAMAGE:    Unauthorized root privilege may result in loss of system
	   and file integrity.
SOLUTIONS: Change the "guest" account entry in /etc/passwd to specify
	   /bin/false as the shell. This vulnerability will be fixed
	   in a future release of Ultrix.
	   Critical DECnet-Internet Gateway Vulnerability Facts

The ULTRIX V4.0, V4.1, and V4.2 DECnet-Internet Gateway software can
be exploited to gain root privilege on the ULTRIX Gateway host. This
vulnerability exists on both the VAX and RISC architectures. It can
only be exploited on ULTRIX V4.0, V4.1, and V4.2 machines running
DECnet/ULTRIX with the DECnet gateway functionality enabled.  To
determine if your ULTRIX host running DECnet/ULTRIX is currently
vulnerable, execute the command:

	/usr/bin/ncp show exec char

	Note: if your system doesn't have the file /usr/bin/ncp, it
	does not have DECnet/ULTRIX installed.

Find the "Gateway Access" line. It should look like:

	Gateway Access                  = Disabled
	Gateway Access                  = Enabled

If gateway access is "Enabled", your machine is vulnerable.

Digital Equipment Corporation (DEC) is aware of this vulnerability and
will correct the problem in a future release of Ultrix. To protect
ULTRIX V4.0, V4.1, and V4.2 systems, DEC has provided the following

	Edit /etc/passwd to specify "/bin/false" in the shell field
	of the "guest" account. Note that this action will effectively
	disable interactive use of the "guest" account.

For example, the /etc/passwd entry
        guest:Nologin:269:31:DECnet Guest:/usr/users/guest:/bin/csh
should become
        guest:Nologin:269:31:DECnet Guest:/usr/users/guest:/bin/false
        ^^^^^                                              ^^^^^^^^^^
	Note that the fields highlighted above must appear verbatim; the
	other fields may vary depending on your local configuration.
	However, CIAC and DEC strongly recommend that the password field
	be "Nologin" (the ULTRIX/DECnet default). ULTRIX uses the "guest"
	account solely to facilitate DECnet/ULTRIX. Any other use of the
	"guest" account is not supported and is strongly discouraged.

CIAC and DEC recommend this workaround be applied to all ULTRIX V4.0,
V4.1, and V4.2 machines running DECnet/ULTRIX, even those with the
gateway functionality disabled, as a prudent precaution.

For additional information or assistance, please contact CIAC:
	Hal R. Brand
        (510)** 422-6312 or (FTS) 532-6312

 	During work hours call CIAC at (510)** 422-8193 or (FTS) 532-8193
	or send e-mail to ciac@llnl.gov.

 	Send FAX messages to: (510)** 423-8002 or (FTS) 543-8002 (THIS

	Previous CIAC bulletins are available via anonymous FTP from
	irbis.llnl.gov (

	** (510) is CIAC's new area code. It was (415).

CIAC thanks Becky Bolling and Curt Bemis of Oak Ridge National
Laboratory for bringing this problem to our attention. CIAC also thanks
Digital Equipment Corporation for the workaround information.  Neither
the United States Government nor the University of California nor any of
their employees, makes any warranty, expressed or implied, or assumes
any legal liability or responsibility for the accuracy, completeness, or
usefulness of any information, product, or process disclosed, or
represents that its use would not infringe privately owned rights.
Reference herein to any specific commercial products, process, or
service by trade name, trademark manufacturer, or otherwise, does not
necessarily constitute or imply its endorsement, recommendation, or
favoring by the United States Government or the University of
California.  The views and opinions of authors expressed herein do not
necessarily state or reflect those of the United States Government nor
the University of California, and shall not be used for advertising or
product endorsement purposes.

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