RSHSVC Included in WinNT 3.5x/4.0 ResKit Has Potential Leak

• Microsoft Windows NT Workstation versions 3.5, 3.51, and 4.0
• Microsoft Windows NT Server versions 3.5, 3.51, and 4.0

SYMPTOMS

Although the RSHSVC utility included in the Windows NT Server Resource Kit uses the .Rhosts file for the Account Level Equivalence (ALE) security, RSHSVC does not do the ALE security check as is explicitly specified in the Rshsvc.txt or Rshsvc.htm files, therefore it poses a security leak or hole.

MORE INFORMATION

A Remote Shell Server Service (RSH) Daemon normally provides one or two levels of security: the Host Level Equivalence (low/loose), by using the Hosts.equiv file and the Account Level Equivalence (high/tighter), by using the .Rhosts file (The period "." is part of the name!).

According to the Rshsvc.txt or Rshsvc.htm file, the Rshsvc.exe file running on an IP host (local computer) provides the ALE security and is supposed to check the user name (either the client user name or server user name) of a user who tries to remotely access from a remote host, and the remote host name against the entries in the .Rhosts file under the %SystemRoot%\System32\Drivers\Etc directory on the local computer.

RSHSVC supposedly returns an access denied error message when any of the following conditions occur:

• The RSH client computer name is not specified in the .Rhosts file.
• The name of the user that is logged on to the RSH client computer is not present in the .Rhosts files.
• RHSVC (using GetHostByName) failed to resolve the IP Address of a computer, say Mx, specified in the .Rhosts files and a user is trying to access this service from that computer Mx.

This poses serious security problems such as delete file, kill process, and so forth. * 2. Issue the following command from an authorized remote computer. (But

STATUS

Microsoft has confirmed this to be a problem in NT version 3.5x/4.0 and we are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

REFERENCE

1. Rshsvc.txt or Rshsvc.htm coming with the Rshsvc.exe and .DLL file in the Windows NT Resource Kit.

2. Essential System Administration, O'Reilly & Assoc, 2nd Ed., Chapter 13 Network Security, Pages 622-623.

3. UNIX Network Programming, W. R. Stevens, Prentice Hall, Chapter 9 Security, Pages 421-424