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Re: Potential Denial of Service Vulnerability in embedded commands - Bas

From: Chet Ramey
Subject: Re: Potential Denial of Service Vulnerability in embedded commands - Bash version 4.4.12(1) - Release
Date: Tue, 7 Nov 2017 10:06:43 -0500
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On 11/7/17 9:56 AM, Alex Nichols wrote:
> Thank you for taking the time to respond to my email. 
> I accept that this is likely not a security issue outside of being a social
> engineering attack, but the  buggy behaviour that i'm curious about is that
> in each case the allocation should only have been of 2147483647 bytes in
> size (the size of the file i was using cat on). but instead, according to
> the error, bash had attempted to allocate far more memory than was required
> which is what caused the crash. for example the Kali example attempted to
> allocate 18446744071562067968 bytes or roughly 18446744071 GB of memory.
> Its also worth noting that the Kali example should have been able to have
> allocated more than enough memory to hold the 2GB file since it was able to
> allocate up to 4296613888 bytes of heap memory when it crashed. 

That depends on the behavior of the memory allocator under Kali. Bash's
power-of-two malloc sometimes causes requests to correspondingly exceed
the requested size, but any allocator (or allocation strategy) will
eventually exceed the available memory.

``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://cnswww.cns.cwru.edu/~chet/

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