-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 fetchmail-SA-2007-01: APOP considered insecure Topics: APOP authentication insecure, fetchmail implementation lax Author: Matthias Andree Version: 1.1 Announced: 2007-04-06 Type: password theft when under MITM attack Impact: password disclosure possible Danger: low Credits: Gaƫtan Leurent CVE Name: CVE-2007-1558 URL: http://fetchmail.sourceforge.net/fetchmail-SA-2007-01.txt Project URL: http://fetchmail.sourceforge.net/ Affects: fetchmail release < 6.3.8 Not affected: fetchmail release 6.3.8 Corrected: 2007-03-18 fetchmail SVN 0. Release history ================== 2007-04-06 1.0 first release 2008-04-24 1.1 add --ssl to section 3. suggestion A below 1. Background ============= 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. 2. Problem description and Impact ================================= The POP3 standard, currently RFC-1939, has specified an optional, MD5-based authentication scheme called "APOP". APOP should no longer be considered secure. Additionally, fetchmail's POP3 client implementation has been validating the APOP challenge too lightly and accepted random garbage as a POP3 server's APOP challenge, rather than insisting that the APOP challenge conformed to RFC-822, as required by RFC-1939. This made it easier than necessary for man-in-the-middle attackers to retrieve by several probing and guessing the first three characters of the APOP secret, bringing brute forcing the remaining characters well within reach. 3. Solution =========== Either of these is currently considered sufficient. A. Only use APOP on SSL or TLS secured connections with mandatory and thorough certificate validation, such as fetchmail --sslproto tls1 --sslcertck or --ssl --sslproto ssl3 --sslcertck), or equivalent in the run control file. B. Avoid APOP and use stronger authenticators. C. If you must continue to use APOP without SSL/TLS, then install fetchmail 6.3.8 or newer, as it is less susceptible to the attack by validating the APOP challenge more strictly to make the attack harder. The fetchmail 6.3.8 source code is available from . A. Copyright, License and Warranty ================================== (C) Copyright 2007, 2008 by Matthias Andree, . 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. END OF fetchmail-SA-2007-01.txt -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) iEYEARECAAYFAlN9DK0ACgkQvmGDOQUufZXpcQCgxzyViEuWv9/kZ6aE8PvfeEev 8ZsAoLQCAZbK1MHuP/FLeviuVOeHRxO1 =FH2Q -----END PGP SIGNATURE-----