Re: .exrc file security risks

On Tue, 29 Apr 2003, Paul Greene wrote:

> I'm verifying the validity of a Solaris hardening guide and came across
> a recommendation to remove ".exrc" files.

Who is the author if this guide ?  This isn't a very common recommendation.

> However, I can't find anything
> mentioning ".exrc" files  in any of the standard security guidelines I
> normally refer to (CISecurity and NSA).

The .exrc file is the configuration file for the ex(1) and vi(1) text file
editors.

From vi(1):

     The editing environment defaults  to  certain  configuration
     options.  When  an editing session is initiated, vi attempts
     to read the EXINIT environment variable. If it  exists,  the
     editor  uses  the  values  defined  in EXINIT; otherwise the
     values set in $HOME/.exrc are used. If $HOME/.exrc does  not
     exist, the default values are used.

     To use a copy of .exrc  located  in  the  current  directory
     other   than  $HOME,  set  the  exrc  option  in  EXINIT  or
     $HOME/.exrc  . Options set in EXINIT can be turned off in  a
     local .exrc only if exrc is set in EXINIT or $HOME/.exrc.

Based on the above a "safe" configuration would be to set the value of
EXINIT to "set noexrc" and create a /.exrc file with "set noexrc" specified.

> What, if any, are the risks associated with these files? (Or possibly
> the spelling ".exrc" is a typo and should be something else?)

You can map keystrokes in vi to run external commands or combinations of
other vi internal commands.


If you are this concerned about your admin environment then maybe you
would be interested in running Trusted Solaris.  Trusted Solaris ships
with a version of vi(1) called adminvi(1) which has disabled a number
of "potentially risky" features, one of them being the ability to run
external commands.  By default the administration roles in Trusted Solaris
use adminvi(1) rather than vi(1).

-- 
Darren J Moffat