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fetchmail-EN-2010-03: fetchmail SASL bugs prevent successful authentication

Topics:		Authentication incapability in older fetchmail versions

Author:		Matthias Andree

Version:	1.0

Announced:	2010-10-16

Impact:		Denial of service

URL:		http://www.fetchmail.info/fetchmail-EN-2010-03.txt

Project URL:	http://www.fetchmail.info/

Affects:	fetchmail up to and including 6.3.17

Not affected:	fetchmail release 6.3.18 and newer

Corrected:	2010-10-09 Git, required commit:

		cc50a92a07e864c3be6a895f2f7daaa426814d45

		(note that you need to check out all changes up to this

		 commit, just cherry-picking this will not suffice)

		2010-10-09 fetchmail 6.3.18 release tarball

0. Release history

==================

2010-10-16 1.0	complete

1. Background

=============

This first "fetchmail-EN" is an errata notice, issued to notify

fetchmail users and distributors of critical bugs that do not, however,

expose the computer running fetchmail to security (privacy, integrity or

availability) threats. The numbering is inlined with the fetchmail

security advisory numbering for redundancy.

fetchmail is a software package to retrieve mail from remote POP2, POP3,

IMAP, ETRN or ODMR servers and forward it to local SMTP, LMTP servers or

message delivery agents. It supports SSL and TLS security layers through

the OpenSSL library, if enabled at compile time and if also enabled at

run time.

2. Problem description and Impact

=================================

Fetchmail can be configured at compile time to support various AUTH or

SASL schemes.

Some of the schemes, notably GSSAPI, can fail in the middle of the

protocol data exchange.  In this case, the client (fetchmail) is

supposed to abort the authentication by sending a line with just an

asterisk "*".

However, all fetchmail versions before 6.3.18 have not aborted failing

authenticators properly (but just sent an empty line).

This caused fetchmail to pick up the authentication error too late and

mistake it for an error to a different scheme it tried later on.

Notably, GSSAPI-enabled fetchmail was frequently reported to fail

authentication against Exchange 2007 or 2010 through Debian bug trackers

and the fetchmail mailing lists.  This is considered sufficiently grave

to warrant an erratum notice.  This is a bug affecting fetchmail 6.3.17

and all previous releases.

3. Solution

===========

Install fetchmail release 6.3.18 or newer.

The fetchmail source code is always available from

<http://developer.berlios.de/project/showfiles.php?group_id=1824>.

Since the changes are non-trivial, 6.3.18 contains other unrelated

important fixes (such as applying timeout to the authentication phase,

or mispicking an incompatible libmd5.so), and because only full releases

have been tested, no separate patch is made available.

For details on what else changed in release 6.3.18, please see the NEWS

file shipping with fetchmail 6.3.18, or its online copy at

<http://developer.berlios.de/project/shownotes.php?group_id=1824&release_id=17957>.

4. Workaround

=============

Configure the required authentication scheme explicitly in the rcfile

or on the command line.  When using TLS or SSL, and --sslcertck is in

effect, that might be --auth password on the command line. (In the

rcfile, the "--" have to be omitted.)

A. Copyright, License and Warranty

==================================

(C) Copyright 2010 by Matthias Andree, <matthias.andree@gmx.de>.

Some rights reserved.

This work is licensed under the

Creative Commons Attribution-NoDerivs 3.0 Germany License (CC BY-ND 3.0).

To view a copy of this license, visit

http://creativecommons.org/licenses/by-nd/3.0/de/deed.en

or send a letter to:

Creative Commons

444 Castro Street

Suite 900

MOUNTAIN VIEW, CALIFORNIA 94041

USA

THIS WORK IS PROVIDED FREE OF CHARGE AND WITHOUT ANY WARRANTIES.

Use the information herein at your own risk.

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