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Date: Sat, 31 Dec 2011 14:26:59 -0700
From: Kurt Seifried <kseifrie@...hat.com>
To: oss-security@...ts.openwall.com
CC: Sebastian Pipping <sebastian@...ping.org>
Subject: Re: mpack 1.6 allows eavesdropping on mails sent by
other users
On 12/31/2011 12:39 PM, Sebastian Pipping wrote:
> Hello oss-security,
>
>
> I think I have found something :-)
>
>
> Target software
> ===============
> I recently stumbled upon a vulnerability in mpack 1.6 [1], a handy tool
> to (1) wrap/unwrap files into/from MIME containers and (2) send files
> via e-mail from the command line.
>
>
> Potential damage
> ================
> The vulnerability allows to eavesdrop on mails (or parts of them on
> FreeBSD) sent by other any user on the system, including mails sent by
> root. I guess "information disclosure" is the term.
>
> To reduce the probability of telling something here that turns out wrong
> later, I wrote a little tool called "mpacktrafficripper" [2] to
> demonstrate and verify the exploit.
>
> The FreeBSD version may allow additional damage, see details below.
>
>
> Affected distros
> ================
> So far I have superficially tested the latest editions of three major
> distros. The results:
>
> - Debian (1.6-7): vulnerable
>
> - Gentoo (1.6-r1): vulnerable
>
> - FreeBSD (1.6): vulnerable (part 2 and after if split,
> see details)
>
> Check [3] for my Git repo collecting the patches of all of these.
>
>
> Technical details
> =================
> The original code of mpack 1.6 operates this way:
>
> 1) make a tempfile name using mktemp
>
> 2) open that file using open(..., O_CREAT|O_EXCL, 0644)
> 3) write to the file ^^^^
> 4) close it
>
> 5) re-open the file using fopen(..., "r")
> 6) read from it
> 7) close it
>
> 8) delete the file
>
> So due to permissions 0644 everyone can read the file he opens the file
> for reading before it's deleted. With an open file descriptor, there
> should not even be a reason to hurry.
>
> So a call like
>
> # sudo mpack -s foo /etc/passwd fake@...l.com
>
> can be eavesdropped on in Debian and Gentoo.
> When instructing mpack to split the file into several mails as in
>
> # sudo mpack -s foo -m 1700 /etc/passwd fake@...l.com
> ^^^^^^^
> the tempfile names follow a pattern:
>
> foo
> foo.01
> foo.02
>
> Now on FreeBSD the original use of mktemp followed by open with
> O_CREAT|O_EXCL has been adjusted to this procedure, instead:
>
> 1) make a temp file using mkstemp and close returned file descriptor
> ^
> 2) open that file using open(..., O_CREAT|O_TRUNC, 0644)
> ^^^^^^^
> 3) to 8) as above
>
> So mkstemp creates the first file (not open) which gets the permissions
> right but all following files are created using open _without_ O_EXCL
> and with 0644 permissions. So the second part and after can be
> eavesdropped on FreeBSD, too. Additionally, there could be room for
> symlink or hardlink attacks in that case, I have tested that.
>
>
> A patch
> =======
> A patch could be to change create files with 0600 permissions rather
> than 0644 as done by [4]. However, that approach affects creation of
> non-temporary files too. In some cases, users may not want that
> behaviour -- you tell me.
>
>
> Upstream
> ========
> My attempts of contacting upstream failed. I wrote to
>
> To: mpack-bugs@...rew.cmu.edu
> CC: "John G. Myers" <jgm@....edu>,
> "Christopher J. Newman" <chrisn@....edu>
>
> and got this back:
>
> ----- The following addresses had permanent fatal errors -----
> <jgm@....edu>
> (reason: 553 5.3.0 <jgm+@...rew.cmu.edu>... Unknown address.
> See <http://www.cmu.edu/directory?to=jgm>)
> niftytelnet@....com
> (reason: 550 5.1.1 unknown or illegal alias: niftytelnet@....com)
> (expanded from: <chrisn@....edu>)
>
> ----- Transcript of session follows -----
> ... while talking to mx1.andrew.cmu.edu.:
> >>> DATA
> <<< 553 5.3.0 <jgm+@...rew.cmu.edu>... Unknown address.
> See <http://www.cmu.edu/directory?to=jgm>
> 550 5.1.1 <jgm@....edu>... User unknown
> <<< 503 5.0.0 Need RCPT (recipient)
> ... while talking to mx.mac.com.akadns.net.:
> >>> DATA
> <<< 550 5.1.1 unknown or illegal alias: niftytelnet@....com
> 550 5.1.1 niftytelnet@....com... User unknown
> <<< 554 5.5.0 No recipients have been specified.
>
>
> Next steps
> ==========
> You tell me. Does this need a CVE number? With a dead upstream, how do
> we best get this fixed in all distros ?
It's a vuln so yup. Please use CVE-2011-4919 for this issue. As for
getting it fixed FreeBSD/Debian/etc monitor this list, if anyone thinks
additional notification is needed please forward this email to the
appropriate parties I guess.
>
> Best,
>
>
>
> Sebastian
>
>
> [1] ftp://ftp.andrew.cmu.edu/pub/mpack/
> [2] http://git.goodpoint.de/?p=mpacktrafficripper.git;a=summary
> [3] http://git.goodpoint.de/?p=mpack.git;a=summary
> [4]
> http://git.goodpoint.de/?p=mpack.git;a=commitdiff;h=0c87201f64491575350b18d04c62ec142e119d1f
Happy new years!
--
-- Kurt Seifried / Red Hat Security Response Team
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