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RE: Bug in syntax checking causes unintended running of a function


From: dnade.ext
Subject: RE: Bug in syntax checking causes unintended running of a function
Date: Thu, 21 Apr 2016 07:40:16 +0000

Hi

 

For the record it does not work with "fake" exported functions. I was scared this could be really bad be so I've tested this case :

 

Here is inject.py

#!/usr/bin/python -tt

import os

os.putenv('BASH_FUNC_foo%%', '''() { avg=0;

avg=((avg+6));

echo -n "This function was never called. Bash version:";

/bin/bash --version | head -1;

}''')

os.system("bash")

 

And, it happily failed:

$ python inject.py        

bash: foo: ligne 1: Erreur de syntaxe près du symbole inattendu « ( »

bash: foo: ligne 1: ` avg=((avg+6));'

bash: avertissement : foo: ignoring function definition attempt

bash: erreur lors de l'import de la définition de fonction pour « foo »

$

 

I think the shellshock mitigations have blocked the injection from happening.

Do you think these should/could be applied to all function definitions?

 

Regards.

 

            D

 

--

Damien Nadé <address@hidden>

Astek Sud-Est pour Orange/OF/DTSI/DSI/DSI DFY/HBX/GOT

 

From: bug-bash [mailto:bug-bash-bounces+address@hidden On Behalf Of David Maas
Sent: lundi 18 avril 2016 21:52
To: address@hidden
Subject: Bug in syntax checking causes unintended running of a function

 

Hi! I found a bug in bash, I've checked versions 4.1 (centos 6.7), 4.2 (centos 7.2), and 4.3.30 (from the ftp site). The bug is that if you do a double parenthesis math thing with the wrong syntax, the script runs the function during what I assume is syntax checking. Demonstration script is attached.


-------------- Script --------------

#!/bin/bash

#Should be avg=((avg+6))


function neverrunme
{
    avg=0
    avg=(($avg+6))
    echo -n "This function was never called. Bash version:"
    /bin/bash --version | head -1
}

echo "Welcome to this demonstration."

-------------- Output --------------

address@hidden ~]$ ./test-file.sh
./test-file.sh: line 7: syntax error near unexpected token `('
./test-file.sh: line 7: `    avg=(($avg+6))'
This function was never called. Bash version:GNU bash, version 4.2.46(1)-release (x86_64-redhat-linux-gnu)
./test-file.sh: line 10: syntax error near unexpected token `}'
./test-file.sh: line 10: `}'

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