Date: Sat, 31 Dec 2011 20:39:13 +0100 From: Sebastian Pipping <sebastian@...ping.org> To: oss-security@...ts.openwall.com Subject: mpack 1.6 allows eavesdropping on mails sent by other users 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 ? 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
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