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Re: Arbitrary command execution in shell - by design!

From: Ángel
Subject: Re: Arbitrary command execution in shell - by design!
Date: Sat, 30 Oct 2021 23:44:34 +0200

On 2021-10-29 at 22:41 -0700, L A Walsh wrote:
> > This is quite unfair.  
> Huh?  It's true--look at how functions have to be stored in
> the environment because someone was able to hack "their
> own system" where they already have unrestricted shell access.
> If that isn't ugly or lame, what is?  But it was the fault
> of taking actions that a hacker could do on a system where
> they already had shell access to corrupt their own environment.

No. The big issue was that web servers convert HTTP headers into
environment variables when calling a CGI script (adding a HTTP_ prefix
which didn't help here), but that allowing a *remote* user to set
certain environment variables that lead to execution if the CGI itself
was a shell script run under bash or bash got called from it.

Two features were safe when taken separately, but turned out to be 
dangerous when combined.

A bug that is only self-exploitable isn't really a security issue.

> If permissions and paths were correctly set to never execute
> files owned by that user, I don't see how that exploit
> would gain root access and affect anyone other the user
> who was injecting the code into their own function.

That exploit didn't allow escalating to root (by itself). It would
typically allow execution as a web user (www-data, apache…) or the
owner of the CGI file. Escalation to root would need to be a separate


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