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fetchmail-SA-2006-02: TLS enforcement problem/MITM attack/password exposure
Topics: fetchmail cannot enforce TLS
Author: Matthias Andree Version: 1.0 Announced: 2007-01-04 Type: secret information disclosure Impact: fetchmail can expose cleartext password over unsecure link fetchmail may not detect man in the middle attacks Danger: medium Credits: Isaac Wilcox (bug report, testing, collaboration on fix) CVE Name: CVE-2006-5867 URL: http://fetchmail.berlios.de/fetchmail-SA-2006-02.txt Project URL: http://fetchmail.berlios.de/
Affects: fetchmail releases <= 6.3.5 fetchmail release candidates 6.3.6-rc1, -rc2, -rc3
Not affected: fetchmail release candidates 6.3.6-rc4, -rc5 fetchmail release 6.3.6
Corrected: 2006-11-26 fetchmail 6.3.6-rc4
2006-11-16 v0.01 internal review draft 2006-11-26 v0.02 revise failure cases, workaround, add acknowledgments 2006-11-27 v0.03 add more vulnerabilities 2006-01-04 v1.0 ready for release
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.
fetchmail ships with a graphical, Python/Tkinter based configuration utility named "fetchmailconf" to help the user create configuration (run control) files for fetchmail.
Fetchmail has had several nasty password disclosure vulnerabilities for a long time. It was only recently that these have been found.
V1. sslcertck/sslfingerprint options should have implied "sslproto tls1" in order to enforce TLS negotiation, but did not.
V2. Even with "sslproto tls1" in the config, fetches would go ahead in plain text if STLS/STARTTLS wasn't available (not advertised, or advertised but rejected).
V3. POP3 fetches could completely ignore all TLS options whether available or not because it didn't reliably issue CAPA before checking for STLS support - but CAPA is a requisite for STLS. Whether or not CAPAbilities were probed, depended on the "auth" option. (Fetchmail only tried CAPA if the auth option was not set at all, was set to gssapi, kerberos, kerberos_v4, otp, or cram-md5.)
V4. POP3 could fall back to using plain text passwords, even if strong authentication had been configured.
V5. POP2 would not complain if strong authentication or TLS had been requested.
This can cause eavesdroppers to obtain the password, depending on the authentication scheme that is configured or auto-selected, and subsequently impersonate somebody else when logging into the upstream server.
If your upstream offers SSLv3-wrapped service on a dedicated port, use fetchmail --ssl --sslcertck --sslproto ssl3 on the command line, or equivalent in the run control file. This encrypts the whole session.
Download and install fetchmail 6.3.6 or a newer stable release from fetchmail's project site at <http://developer.berlios.de/project/showfiles.php?group_id=1824>.
Isaac Wilcox has been a great help with testing the fixes and getting them right.
(C) Copyright 2007 by Matthias Andree, <firstname.lastname@example.org>. Some rights reserved.
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs German License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/2.0/de/ or send a letter to Creative Commons; 559 Nathan Abbott Way; Stanford, California 94305; USA.
THIS WORK IS PROVIDED FREE OF CHARGE AND WITHOUT ANY WARRANTIES. Use the information herein at your own risk.
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