Filename: 129-reject-plaintext-ports.txt Title: Block Insecure Protocols by Default Version: $Revision$ Last-Modified: $Date$ Author: Kevin Bauer & Damon McCoy Created: 2008-01-15 Status: Open Overview: Below is a proposal to mitigate insecure protocol use over Tor. This document 1) demonstrates the extent to which insecure protocols are currently used within the Tor network, and 2) proposes a simple solution to prevent users from unknowingly using these insecure protocols. By insecure, we consider protocols that explicitly leak sensitive user names and/or passwords, such as POP, IMAP, Telnet, and FTP. Motivation: As part of a general study of Tor use in 2006/2007 [1], we attempted to understand what types of protocols are used over Tor. While we observed a enormous volume of Web and Peer-to-peer traffic, we were surprised by the number of insecure protocols that were used over Tor. For example, over an 8 day observation period, we observed the following number of connections over insecure protocols: POP and IMAP:10,326 connections Telnet: 8,401 connections FTP: 3,788 connections Each of the above listed protocols exchange user name and password information in plain-text. As an upper bound, we could have observed 22,515 user names and passwords. This observation echos the reports of a Tor router logging and posting e-mail passwords in August 2007 [2]. The response from the Tor community has been to further educate users about the dangers of using insecure protocols over Tor. However, we recently repeated our Tor usage study from last year and noticed that the trend in insecure protocol use has not declined. Therefore, we propose that additional steps be taken to protect naive Tor users from inadvertently exposing their identities (and even passwords) over Tor. Security Implications: This proposal is intended to improve Tor's security by limiting the use of insecure protocols. Roger added: By adding these warnings for only some of the risky behavior, users may do other risky behavior, not get a warning, and believe that it is therefore safe. But overall, I think it's better to warn for some of it than to warn for none of it. Specification: As an initial step towards mitigating the use of the above-mentioned insecure protocols, we propose that the default ports for each respective insecure service be blocked at the Tor client's socks proxy. These default ports include: 23 - Telnet 109 - POP2 110 - POP3 143 - IMAP Notice that FTP is not included in the proposed list of ports to block. This is because FTP is often used anonymously, i.e., without any identifying user name or password. This blocking scheme can be implemented as a set of flags in the client's torrc configuration file: BlockInsecureProtocols 0|1 WarnInsecureProtocols 0|1 When the warning flag is activated, a message should be displayed to the user similar to the message given when Tor's socks proxy is given an IP address rather than resolving a host name. We recommend that the default torrc configuration file block insecure protocols and provide a warning to the user to explain the behavior. Finally, there are many popular web pages that do not offer secure login features, such as MySpace, and it would be prudent to provide additional rules to Privoxy to attempt to protect users from unknowingly submitting their login credentials in plain-text. Compatibility: None, as the proposed changes are to be implemented in the client. References: [1] Shining Light in Dark Places: A Study of Anonymous Network Usage. University of Colorado Technical Report CU-CS-1032-07. August 2007. [2] Rogue Nodes Turn Tor Anonymizer Into Eavesdropper's Paradise. http://www.wired.com/politics/security/news/2007/09/embassy_hacks. Wired. September 10, 2007. Implementation: Roger added this feature in http://archives.seul.org/or/cvs/Jan-2008/msg00182.html He also added a status event for Vidalia to recognize attempts to use vulnerable-plaintext ports, so it can help the user understand what's going on and how to fix it. Next steps: a) Vidalia should learn to recognize this controller status event, so we don't leave users out in the cold when we enable this feature. b) We should decide which ports to reject by default. The current consensus is 23,109,110,143 -- the same set that we warn for now.