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Re: Vulnerability in Majordomo
From: merlyn () STONEHENGE COM (Randal Schwartz)
Date: Tue, 26 Aug 1997 18:45:55 -0700


"Steve" == Steve Hill <steve_hill () VNET IBM COM> writes:

Steve> By far the safest way of doing any sort of validation is to
Steve> provide a list of the safe characters, and not permit anything
Steve> else. The perl to implement such a scheme is remarkably simple:

Steve>   $reply_addr =~ s/[^\w\. () -]//g;

Steve> This will remove all characters which are not alphanumeric, a
Steve> period, an at symbol or a hyphen. Of course, you may like to
Steve> include a small piece of code which saves insecure strings in a
Steve> file somewhere, along with the sender.

No.  The *very* safest way is "Don't let data anywhere near a shell!"
The CGI FAQ tells how to do this stuff right.  So does the Perl FAQ
(which now ships *with* Perl as part of the distribution).  So does
the (new) Camel book.

There's no excuse for letting data of any kind get anywhere near a
shell line.  Ugh.  Especially with the ultra-flexible Perl constructs.

--
Name: Randal L. Schwartz / Stonehenge Consulting Services (503)777-0095
Keywords: Perl training, UNIX[tm] consulting, video production, skiing, flying
Email: <merlyn () stonehenge com> Snail: (Call) PGP-Key: (finger merlyn () ora com)
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Quote: "I'm telling you, if I could have five lines in my .sig, I would!" -- me



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