Re: Bug in bash <= 4.3 [security feature bypassed]

[Hector Marco <hecmargi () upv es>]

On 05/06/14 12:02, Daryl Tester wrote:
> On 03/06/14 23:46, Hector Marco wrote:
>
> > Recently we discovered a bug in bash. After some time after reporting
> > it to bash developers, it has not been fixed.
>
> ...
>
> > Any comments about this issue are welcomed.
> >
> > Details at:
> > http://hmarco.org/bugs/bash_4.3-setuid-bug.html
>
> I'm only going by the patch presented above, so ...
>
> 1.  The program should be calling setgid() before setuid() (which is
> another common class of security mistake).
> 2.  Why is exit() returning values greater than 255?  It's not capable
> of doing that under (most) Unix environments.


a) I tried to patch by doing minimal changes to bash source code. 
Originally,
    the bash call first setuid() and later setgid(). And as you point 
this is not the
    best option. So, this code has actually 2 mistakes. I changed the 
patch code
    order calls, thanks, but anyway the patch achieve their goal, 
"avoid the bash
    to be a valid target shell in an attack".


b) I can imagine why you spent time writing about the patch and not 
about the
    important point here which is the bug.