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Date: Fri, 23 Oct 2015 07:15:53 +0100
From: Tim Brown <>
Subject: Re: CVE Request: BusyBox tar directory traversal

On Thursday 22 October 2015 22:40:29 Robert Watson wrote:
> Apologies if I'm naive but... since /tmp is world writable, how is this a
> vulnerability?

The permissions on /tmp having nothing at all to do with this, not sure why 
you brought that up. With most archiving tools, there is an expectation that 
unpacking will involve writing only to the current directory and below and/or 
a user specified directory and below. This breaks that assumption because the 
unpacker may create a symlink to a location outside of the directory which 
later may then be followed when further files are unpacked. Depending on the 
user permissions, this could lead to sensitive files being overwritten. Even if 
the unpacker validates the path it is writing to is as described, the 
validation fails to account for the potential presence of symbolic link files 
that point elsewhere.

Tim Brown
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