[38365] in bugtraq
Re: gzip TOCTOU file-permissions vulnerability
daemon@ATHENA.MIT.EDU (psz@maths.usyd.edu.au)
Thu Apr 14 14:27:18 2005
From: psz@maths.usyd.edu.au
Date: Thu, 14 Apr 2005 10:29:21 +1000
Message-Id: <200504140029.j3E0TLCd005292@pisa.maths.usyd.edu.au>
To: 299007@bugs.debian.org, joeyh@debian.org, martin.pitt@canonical.com
Cc: 303927@bugs.debian.org, bugtraq@securityfocus.com, imranghory@gmail.com
In-Reply-To: <20050413154049.GA30175@kitenet.net>
Joey Hess <joeyh@debian.org> wrote:
>> ... really dumb idea to have a group/world-writeable directory
>> without the sticky bit.
>
> It may be really dumb, but it's pretty common practice too. ...
> Just a few examples within the Debian project ...
Kindly add the Debian example:
psz@pisa:/usr/local$ ls -ld .
drwxrwsr-x 10 root staff 4096 Nov 13 2002 .
For Debian this is "mandated by policy":
> The Debian Policy Manual [1] says:
>
> ... /usr/local take precedence over the equivalents in /usr.
> ... should have permissions 2775 and be owned by root.staff.
>
> but it [2] also says:
>
> ... make sure that [it] is secure ...
> Files should be owned by root.root ... mode 644 or 755.
> Directories should be mode 755 or 2775 ... owned by the group that needs
> write access to it.
>
> ...
> References:
>
> [1] http://www.debian.org/doc/debian-policy/ch-opersys.html#s9.1.2
> [2] http://www.debian.org/doc/debian-policy/ch-files.html#s10.9
(please see http://bugs.debian.org/299007 for more details).
> (gzip is not typically ran in any of these directories AFAIK, FWIW).
Typically? Suppose I (as simple user psz) do
cd $HOME; touch xyz; chmod 666 xyz; gzip xyz
and tell my system manager that I have problems with that gzipped file.
While root is running "gunzip ~psz/xyz" I do
rm xyz; ln /etc/passwd xyz
then we end up with /etc/passwd world-writable. (Bzip uses chown also, so
using bzip2/bunzip would get /etc/passwd owned by psz; am not sure about
gzip or cpio.)
Cheers,
Paul Szabo psz@maths.usyd.edu.au http://www.maths.usyd.edu.au/u/psz/
School of Mathematics and Statistics University of Sydney Australia
