First problem: HOW does the client set "the environmental variable BAD_VAR"
The classic example Shellshock is having HTTP_USER_AGENT be your bad variable 
wget -U "() { test;};echo \"Content-type: text/plain\"; echo; echo; /b
+in/cat /etc/passwd" http://10.248.2.15/cgi-bin/test.cgi

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and more generally, the whole point of tainting the whole of %ENV is that you shouldn't be playing catch-up; whole thing is potentially suspect.
where does the script you've shown us access BAD_VAR?
This is exactly my point. The Perl script never accesses BAD_VAR, only the child process. Perhaps this updated case would make my vector more obvious: 
#!/usr/bin/perl -wT

print "Content-type: text/plain\n\n";
local $ENV{PATH} = '/usr/local/bin';
print `eval \$BAD_VAR`;

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The horror with Shellshock is that unless you wipe all potentially corrupted values out of %ENV, it doesn't matter what you call. Thus my original question, should I be updating that script to read 
#!/usr/bin/perl -wT

print "Content-type: text/plain\n\n";
local %ENV = (PATH => '/usr/local/bin');
print `eval \$BAD_VAR`;

[download]

#11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.

In reply to Re^6: Taint and Shellshock by kennethk
in thread Taint and Shellshock by kennethk

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