tahoe-lafs/docs/known_issues.txt

= Known Issues =

1.  Overview
2.  Issues in Tahoe-LAFS v1.6.0, released 2010-02-01
  2.1.  Potential unauthorized access by JavaScript in unrelated files
    2.1.1.  How to manage it
  2.2.  Potential disclosure of file through embedded hyperlinks or JavaScript in that file
    2.2.1.  How to manage it
  2.3.  Command-line arguments are leaked to other local users
    2.3.1.  How to manage it
  2.4.  Capabilities may be leaked to web browser phishing filter servers
    2.4.1.  How to manage it

== Overview ==

Below is a list of known issues in recent releases of Tahoe-LAFS, and how to
manage them.  The current version of this file can be found at

http://allmydata.org/source/tahoe/trunk/docs/known_issues.txt

If you've been using Tahoe-LAFS since v1.1 (released 2008-06-11) or if you're
just curious about what sort of mistakes we've made in the past, then you might
want to read the "historical known issues" document:

http://allmydata.org/source/tahoe/trunk/docs/historical/historical_known_issues.txt

== Issues in Tahoe-LAFS v1.6.0, released 2010-02-01 ==

=== Potential unauthorized access by JavaScript in unrelated files ===

If you view a file stored in Tahoe-LAFS through a web user interface,
JavaScript embedded in that file might be able to access other files or
directories stored in Tahoe-LAFS which you view through the same web
user interface.  Such a script would be able to send the contents of
those other files or directories to the author of the script, and if you
have the ability to modify the contents of those files or directories,
then that script could modify or delete those files or directories.

==== How to manage it ====

For future versions of Tahoe-LAFS, we are considering ways to close off
this leakage of authority while preserving ease of use -- the discussion
of this issue is ticket #615.

For the present, either do not view files stored in Tahoe-LAFS through a
web user interface, or turn off JavaScript in your web browser before
doing so, or limit your viewing to files which you know don't contain
malicious JavaScript.


=== Potential disclosure of file through embedded hyperlinks or JavaScript in that file ===

If there is a file stored on a Tahoe-LAFS storage grid, and that file
gets downloaded and displayed in a web browser, then JavaScript or
hyperlinks within that file can leak the capability to that file to a
third party, which means that third party gets access to the file.

If there is JavaScript in the file, then it could deliberately leak
the capability to the file out to some remote listener.

If there are hyperlinks in the file, and they get followed, then
whichever server they point to receives the capability to the
file. Note that IMG tags are typically followed automatically by web
browsers, so being careful which hyperlinks you click on is not
sufficient to prevent this from happening.

==== How to manage it ====

For future versions of Tahoe-LAFS, we are considering ways to close off
this leakage of authority while preserving ease of use -- the discussion
of this issue is ticket #127.

For the present, a good work-around is that if you want to store and
view a file on Tahoe-LAFS and you want that file to remain private, then
remove from that file any hyperlinks pointing to other people's servers
and remove any JavaScript unless you are sure that the JavaScript is not
written to maliciously leak access.


=== Command-line arguments are leaked to other local users ===

Remember that command-line arguments are visible to other users (through
the 'ps' command, or the windows Process Explorer tool), so if you are
using a Tahoe-LAFS node on a shared host, other users on that host will
be able to see (and copy) any caps that you pass as command-line
arguments.  This includes directory caps that you set up with the "tahoe
add-alias" command.  Use "tahoe create-alias" for that purpose instead.

==== How to manage it ====

Bypass add-alias and edit the NODEDIR/private/aliases file directly, by
adding a line like this:

fun: URI:DIR2:ovjy4yhylqlfoqg2vcze36dhde:4d4f47qko2xm5g7osgo2yyidi5m4muyo2vjjy53q4vjju2u55mfa

By entering the dircap through the editor, the command-line arguments
are bypassed, and other users will not be able to see them. Once you've
added the alias, if you use that alias instead of a cap itself on the
command-line, then no secrets are passed through the command line.  Then
other processes on the system can still see your filenames and other
arguments you type there, but not the caps that Tahoe uses to permit
access to your files and directories.  Starting in Tahoe-LAFS v1.3.0,
there is a "tahoe create-alias" command that does this for you.


=== Capabilities may be leaked to web browser phishing filter servers ===

Internet Explorer includes a "phishing filter", which is turned on by
default, and which sends any URLs that it deems suspicious to a central
server (Microsoft gives a brief description of its operation at
<http://blogs.msdn.com/ie/archive/2005/09/09/463204.aspx>).
This of course has implications for the privacy of general web browsing,
but when using the Tahoe web user interface, it could also affect
confidentiality and integrity by leaking capabilities to the filter server.
Since IE's filter sends URLs by SSL/TLS, the exposure of caps is limited
to the filter server operators (or anyone able to hack the filter server)
rather than to network eavesdroppers.

We are not aware of any other widely used current browser besides IE that
has such a facility enabled by default (Opera has one that is disabled by
default). Firefox briefly included a phishing filter in previous versions,
but abandoned it.

==== How to manage it ====

If you use Internet Explorer's phishing filter or a similar add-on
for another browser, consider either disabling it, or not using the WUI
via that browser. Phishing filters have very limited effectiveness (see
<http://lorrie.cranor.org/pubs/ndss-phish-tools-final.pdf>), and phishing
site operators have learnt how to bypass them.

To disable the filter in IE7 or IE8:
 - Click Internet Options from the Tools menu.
 - Click the Advanced tab.
 - If an "Enable SmartScreen Filter" option is present, uncheck it.
   If a "Use Phishing Filter" or "Phishing Filter" option is present,
   set it to Disable.
 - Confirm (click OK or Yes) out of all dialogs.

If you have a version of IE that splits the settings between security
zones, do this for all zones. Alternatively, don't use IE.