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Re: I've found a vulnerability in bash

From: Kerin Millar
Subject: Re: I've found a vulnerability in bash
Date: Fri, 19 Nov 2021 14:05:00 +0000

(Copying the list back in ...)

On Fri, 19 Nov 2021 07:19:29 -0500
Marshall Whittaker <marshallwhittaker@gmail.com> wrote:

> Though I do disagree with you, this is the only message in this thread that
> even makes sense.

Firstly, rm * is a valid - albeit unsafe - simple command, and one that is 
easily rectified. Secondly, the manner in which * expands is in accordance with 
the documented behaviour. Thirdly, the manner in which simple commands are 
processed is in accordance with the documented behaviour. In the event that you 
can falsify the second and/or third of these assertions, then - and only then - 
will you have discovered a bug in bash.

As far as I can tell, your contention is that the default mode of pathname 
expansion should be changed in order to paper over the first point. Very well. 
Let's consider what would happen if, say, GLOBIGNORE=".*:-*" were to be a 

* bash would violate POSIX [1]
* bash would be incompatible with other shells on this point
* existing scripts would change their behaviour and/or break (note: file names 
beginning with a dash are perfectly legal)
* the behavioural change would not conclusively address the issue

What do I mean by not addressing the issue? Fundamentally, the issue is one of 
passing unsanitised input to an program, with the input taking the form of an 
argument vector. Programs are free to act upon their arguments in whatever way 
they see fit. While it may be common for argument beginning with a dash to 
denote an option, this is by no means a cast-iron rule. If the words produced 
by the expansion of a glob be arbitrary in nature, it is your responsibility to 
understand how to convey them safely to a given program. In many cases, 
assuming that responsibility turns out not to be overly hard. The point is that 
it is beyond the purview of the shell.


Kerin Millar

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