NO RESTRICTIONS _____________________________________________________ The Computer Incident Advisory Capability ___ __ __ _ ___ / | / \ / \___ __|__ /___\ \___ _____________________________________________________ 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 architectures. 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 or 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 workaround: 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 brand1@llnl.gov 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 IS A NEW FAX NUMBER). Previous CIAC bulletins are available via anonymous FTP from irbis.llnl.gov (128.115.19.60) ** (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.