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 , 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"  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  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 . 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 > > >  ftp://ftp.andrew.cmu.edu/pub/mpack/ >  http://git.goodpoint.de/?p=mpacktrafficripper.git;a=summary >  http://git.goodpoint.de/?p=mpack.git;a=summary >  > 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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