Secure setuid shell scripts

[Chris Torek]

>>In article <4409 at bsu-cs.UUCP> dhesi at bsu-cs.UUCP (Rahul Dhesi) asked:
>>>If a 4.3BSD system has not been patched ....

>In article <14069 at mimsy.UUCP> I answered:
>>If the system has not been patched, and there is a set-ID script somewhere,
>>that script can be used as the basis for gaining the privileges granted
>>by that ID (user or group) in a way that the author of the script most
>>likely did not intend.

In article <546 at sp7040.UUCP> sbc at sp7040.UUCP (Stephen Carroll) asks:
>just one question.  Is this problem a security hole for only BSD systems,
>or does it exist on other SVID type systems or others?

Since System Vs% do not have directly-executable scripts, System Vs do
not have the problem, because System Vs cannot possibly have any set-ID
scripts.  (Actually, there is a way to have set-ID scripts without having
the kernel do it: you make the interpreter itself set-ID, and have it
check the ID on the script.  I believe ksh can do this.  sh cannot,
certainly not without modification.)

-----
% Not System V, System Vs: there are many different System Vs, all
  incompatible to some extent.  *Which one* shall we consider standard?
-----

 - If the kernel does not have directly-executable scripts, the system
   does not have the bug.

 - If the kernel has the #! mechanism copied directly from 4BSD, the system
   does have the bug.

 - If the kernel has a modified #! mechanism, it might not have the bug.
 
 - If you have on your machine no scripts that are themselves set-ID (user
   or group), you need not worry about the bug, whether it exists or not
   on your system.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris at mimsy.umd.edu	Path:	uunet!mimsy!chris