templates: properly escape inline JavaScript values TLDR: Kallithea has issues with escaping values for use in inline JS. Despite judicious poking of the code, no actual security vulnerabilities have been found, just lots of corner-case bugs. This patch fixes those, and hardens the code against actual security issues. The long version: To embed a Python value (typically a 'unicode' plain-text value) in a larger file, it must be escaped in a context specific manner. Example: >>> s = u'<script>alert("It\'s a trap!");</script>' 1) Escaped for insertion into HTML element context >>> print cgi.escape(s) &lt;script&gt;alert("It's a trap!");&lt;/script&gt; 2) Escaped for insertion into HTML element or attribute context >>> print h.escape(s) &lt;script&gt;alert(&#34;It&#39;s a trap!&#34;);&lt;/script&gt; This is the default Mako escaping, as usually used by Kallithea. 3) Encoded as JSON >>> print json.dumps(s) "<script>alert(\"It's a trap!\");</script>" 4) Escaped for insertion into a JavaScript file >>> print '(' + json.dumps(s) + ')' ("<script>alert(\"It's a trap!\");</script>") The parentheses are not actually required for strings, but may be needed to avoid syntax errors if the value is a number or dict (object). 5) Escaped for insertion into a HTML inline <script> element >>> print h.js(s) ("\x3cscript\x3ealert(\"It's a trap!\");\x3c/script\x3e") Here, we need to combine JS and HTML escaping, further complicated by the fact that "<script>" tag contents can either be parsed in XHTML mode (in which case '<', '>' and '&' must additionally be XML escaped) or HTML mode (in which case '</script>' must be escaped, but not using HTML escaping, which is not available in HTML "<script>" tags). Therefore, the XML special characters (which can only occur in string literals) are escaped using JavaScript string literal escape sequences. (This, incidentally, is why modern web security best practices ban all use of inline JavaScript...) Unsurprisingly, Kallithea does not do (5) correctly. In most cases, Kallithea might slap a pair of single quotes around the HTML escaped Python value. A typical benign example: $('#child_link').html('${_('No revisions')}'); This works in English, but if a localized version of the string contains an apostrophe, the result will be broken JavaScript. In the more severe cases, where the text is user controllable, it leaves the door open to injections. In this example, the script inserts the string as HTML, so Mako's implicit HTML escaping makes sense; but in many other cases, HTML escaping is actually an error, because the value is not used by the script in an HTML context. The good news is that the HTML escaping thwarts attempts at XSS, since it's impossible to inject syntactically valid JavaScript of any useful complexity. It does allow JavaScript errors and gibberish to appear on the page, though. In these cases, the escaping has been fixed to use either the new 'h.js' helper, which does JavaScript escaping (but not HTML escaping), OR the new 'h.jshtml' helper (which does both), in those cases where it was unclear if the value might be used (by the script) in an HTML context. Some of these can probably be "relaxed" from h.jshtml to h.js later, but for now, using h.jshtml fixes escaping and doesn't introduce new errors. In a few places, Kallithea JSON encodes values in the controller, then inserts the JSON (without any further escaping) into <script> tags. This is also wrong, and carries actual risk of XSS vulnerabilities. However, in all cases, security vulnerabilities were narrowly avoided due to other filtering in Kallithea. (E.g. many special characters are banned from appearing in usernames.) In these cases, the escaping has been fixed and moved to the template, making it immediately visible that proper escaping has been performed. Mini-FAQ (frequently anticipated questions): Q: Why do everything in one big, hard to review patch? Q: Why add escaping in specific case FOO, it doesn't seem needed? Because the goal here is to have "escape everywhere" as the default policy, rather than identifying individual bugs and fixing them one by one by adding escaping where needed. As such, this patch surely introduces a lot of needless escaping. This is no different from how Mako/Pylons HTML escape everything by default, even when not needed: it's errs on the side of needless work, to prevent erring on the side of skipping required (and security critical) work. As for reviewability, the most important thing to notice is not where escaping has been introduced, but any places where it might have been missed (or where h.jshtml is needed, but h.js is used). Q: The added escaping is kinda verbose/ugly. That is not a question, but yes, I agree. Hopefully it'll encourage us to move away from inline JavaScript altogether. That's a significantly larger job, though; with luck this patch will keep us safe and secure until such a time as we can implement the real fix. Q: Why not use Mako filter syntax ("${val|h.js}")? Because of long-standing Mako bug #140, preventing use of 'h' in filters. Q: Why not work around bug #140, or even use straight "${val|js}"? Because Mako still applies the default h.escape filter before the explicitly specified filters. Q: Where do we go from here? Longer term, we should stop doing variable expansions in script blocks, and instead pass data to JS via e.g. data attributes, or asynchronously using AJAX calls. Once we've done that, we can remove inline JavaScript altogether in favor of separate script files, and set a strict Content Security Policy explicitly blocking inline scripting, and thus also the most common kind of cross-site scripting attack.

.. _installation_iis:

=====================================================================
Installing Kallithea on Microsoft Internet Information Services (IIS)
=====================================================================

The following is documented using IIS 7/8 terminology. There should be nothing
preventing you from applying this on IIS 6 well.

.. note::

    Installing Kallithea under IIS can enable Single Sign-On to the Kallithea
    web interface from web browsers that can authenticate to the web server.
    (As an alternative to IIS, SSO is also possible with for example Apache and
    mod_sspi.)

    Mercurial and Git do however by default not support SSO on the client side
    and will still require some other kind of authentication.
    (An extension like hgssoauthentication_ might solve that.)

.. note::

    For the best security, it is strongly recommended to only host the site over
    a secure connection, e.g. using TLS.


Prerequisites
-------------

Apart from the normal requirements for Kallithea, it is also necessary to get an
ISAPI-WSGI bridge module, e.g. isapi-wsgi.


Installation
------------

The following assumes that your Kallithea is at ``c:\inetpub\kallithea``, and
will be served from the root of its own website. The changes to serve it in its
own virtual folder will be noted where appropriate.

Application pool
^^^^^^^^^^^^^^^^

Make sure that there is a unique application pool for the Kallithea application
with an identity that has read access to the Kallithea distribution.

The application pool does not need to be able to run any managed code. If you
are using a 32-bit Python installation, then you must enable 32-bit program in
the advanced settings for the application pool; otherwise Python will not be able
to run on the website and neither will Kallithea.

.. note::

    The application pool can be the same as an existing application pool,
    as long as the Kallithea requirements are met by the existing pool.

ISAPI handler
^^^^^^^^^^^^^

The ISAPI handler can be generated using::

    paster install-iis my.ini --virtualdir=/

This will generate a ``dispatch.py`` file in the current directory that contains
the necessary components to finalize an installation into IIS. Once this file
has been generated, it is necessary to run the following command due to the way
that ISAPI-WSGI is made::

    python2 dispatch.py install

This accomplishes two things: generating an ISAPI compliant DLL file,
``_dispatch.dll``, and installing a script map handler into IIS for the
``--virtualdir`` specified above pointing to ``_dispatch.dll``.

The ISAPI handler is registered to all file extensions, so it will automatically
be the one handling all requests to the specified virtual directory. When the website starts
the ISAPI handler, it will start a thread pool managed wrapper around the paster
middleware WSGI handler that Kallithea runs within and each HTTP request to the
site will be processed through this logic henceforth.

Authentication with Kallithea using IIS authentication modules
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The recommended way to handle authentication with Kallithea using IIS is to let
IIS handle all the authentication and just pass it to Kallithea.

.. note::

    As an alternative without SSO, you can also use LDAP authentication with
    Active Directory, see :ref:`ldap-setup`.

To move responsibility into IIS from Kallithea, we need to configure Kallithea
to let external systems handle authentication and then let Kallithea create the
user automatically. To do this, access the administration's authentication page
and enable the ``kallithea.lib.auth_modules.auth_container`` plugin. Once it is
added, enable it with the ``REMOTE_USER`` header and check *Clean username*.
Finally, save the changes on this page.

Switch to the administration's permissions page and disable anonymous access,
otherwise Kallithea will not attempt to use the authenticated user name. By
default, Kallithea will populate the list of users lazily as they log in. Either
disable external auth account activation and ensure that you pre-populate the
user database with an external tool, or set it to *Automatic activation of
external account*. Finally, save the changes.

The last necessary step is to enable the relevant authentication in IIS, e.g.
Windows authentication.


Troubleshooting
---------------

Typically, any issues in this setup will either be entirely in IIS or entirely
in Kallithea (or Kallithea's WSGI/paster middleware). Consequently, two
different options for finding issues exist: IIS' failed request tracking which
is great at finding issues until they exist inside Kallithea, at which point the
ISAPI-WSGI wrapper above uses ``win32traceutil``, which is part of ``pywin32``.

In order to dump output from WSGI using ``win32traceutil`` it is sufficient to
type the following in a console window::

    python2 -m win32traceutil

and any exceptions occurring in the WSGI layer and below (i.e. in the Kallithea
application itself) that are uncaught, will be printed here complete with stack
traces, making it a lot easier to identify issues.


.. _hgssoauthentication: https://bitbucket.org/domruf/hgssoauthentication