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-Filename: 129-reject-plaintext-ports.txt
-Title: Block Insecure Protocols by Default
-Author: Kevin Bauer & Damon McCoy
-Created: 2008-01-15
-Status: Closed
-Implemented-In: 0.2.0.x
-
-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.
-