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.

List of contributors to Kallithea project:

    Mads Kiilerich <madski@unity3d.com> 2012-2016
    Takumi IINO <trot.thunder@gmail.com> 2012-2016
    Unity Technologies 2012-2016
    Andrew Shadura <andrew@shadura.me> 2012 2014-2016
    Dominik Ruf <dominikruf@gmail.com> 2012 2014-2016
    Thomas De Schampheleire <thomas.de.schampheleire@gmail.com> 2014-2016
    Étienne Gilli <etienne.gilli@gmail.com> 2015-2016
    Jan Heylen <heyleke@gmail.com> 2015-2016
    Robert Martinez <ntttq@inboxen.org> 2015-2016
    Robert Rauch <mail@robertrauch.de> 2015-2016
    Søren Løvborg <sorenl@unity3d.com> 2015-2016
    Angel Ezquerra <angel.ezquerra@gmail.com> 2016
    Asterios Dimitriou <steve@pci.gr> 2016
    Kateryna Musina <kateryna@unity3d.com> 2016
    Konstantin Veretennicov <kveretennicov@gmail.com> 2016
    Oscar Curero <oscar@naiandei.net> 2016
    Robert James Dennington <tinytimrob@googlemail.com> 2016
    timeless@gmail.com 2016
    YFdyh000 <yfdyh000@gmail.com> 2016
    Aras Pranckevičius <aras@unity3d.com> 2012-2013 2015
    Sean Farley <sean.michael.farley@gmail.com> 2013-2015
    Christian Oyarzun <oyarzun@gmail.com> 2014-2015
    Joseph Rivera <rivera.d.joseph@gmail.com> 2014-2015
    Michal Čihař <michal@cihar.com> 2014-2015
    Anatoly Bubenkov <bubenkoff@gmail.com> 2015
    Andrew Bartlett <abartlet@catalyst.net.nz> 2015
    Balázs Úr <urbalazs@gmail.com> 2015
    Ben Finney <ben@benfinney.id.au> 2015
    Branko Majic <branko@majic.rs> 2015
    Daniel Hobley <danielh@unity3d.com> 2015
    David Avigni <david.avigni@ankapi.com> 2015
    Denis Blanchette <dblanchette@coveo.com> 2015
    duanhongyi <duanhongyi@doopai.com> 2015
    EriCSN Chang <ericsning@gmail.com> 2015
    Grzegorz Krason <grzegorz.krason@gmail.com> 2015
    Jiří Suchan <yed@vanyli.net> 2015
    Kazunari Kobayashi <kobanari@nifty.com> 2015
    Kevin Bullock <kbullock@ringworld.org> 2015
    kobanari <kobanari@nifty.com> 2015
    Marc Abramowitz <marc@marc-abramowitz.com> 2015
    Marc Villetard <marc.villetard@gmail.com> 2015
    Matthias Zilk <matthias.zilk@gmail.com> 2015
    Michael Pohl <michael@mipapo.de> 2015
    Michael V. DePalatis <mike@depalatis.net> 2015
    Morten Skaaning <mortens@unity3d.com> 2015
    Nick High <nick@silverchip.org> 2015
    Niemand Jedermann <predatorix@web.de> 2015
    Peter Vitt <petervitt@web.de> 2015
    Ronny Pfannschmidt <opensource@ronnypfannschmidt.de> 2015
    Sam Jaques <sam.jaques@me.com> 2015
    Tuux <tuxa@galaxie.eu.org> 2015
    Viktar Palstsiuk <vipals@gmail.com> 2015
    Ante Ilic <ante@unity3d.com> 2014
    Bradley M. Kuhn <bkuhn@sfconservancy.org> 2014
    Calinou <calinou@opmbx.org> 2014
    Daniel Anderson <daniel@dattrix.com> 2014
    Henrik Stuart <hg@hstuart.dk> 2014
    Ingo von Borstel <kallithea@planetmaker.de> 2014
    Jelmer Vernooij <jelmer@samba.org> 2014
    Jim Hague <jim.hague@acm.org> 2014
    Matt Fellows <kallithea@matt-fellows.me.uk> 2014
    Max Roman <max@choloclos.se> 2014
    Na'Tosha Bard <natosha@unity3d.com> 2014
    Rasmus Selsmark <rasmuss@unity3d.com> 2014
    Tim Freund <tim@freunds.net> 2014
    Travis Burtrum <android@moparisthebest.com> 2014
    Zoltan Gyarmati <mr.zoltan.gyarmati@gmail.com> 2014
    Marcin Kuźmiński <marcin@python-works.com> 2010-2013
    xpol <xpolife@gmail.com> 2012-2013
    Aparkar <aparkar@icloud.com> 2013
    Dennis Brakhane <brakhane@googlemail.com> 2013
    Grzegorz Rożniecki <xaerxess@gmail.com> 2013
    Jonathan Sternberg <jonathansternberg@gmail.com> 2013
    Leonardo Carneiro <leonardo@unity3d.com> 2013
    Magnus Ericmats <magnus.ericmats@gmail.com> 2013
    Martin Vium <martinv@unity3d.com> 2013
    Simon Lopez <simon.lopez@slopez.org> 2013
    Ton Plomp <tcplomp@gmail.com> 2013
    Augusto Herrmann <augusto.herrmann@planejamento.gov.br> 2011-2012
    Dan Sheridan <djs@adelard.com> 2012
    Dies Koper <diesk@fast.au.fujitsu.com> 2012
    Erwin Kroon <e.kroon@smartmetersolutions.nl> 2012
    H Waldo G <gwaldo@gmail.com> 2012
    hppj <hppj@postmage.biz> 2012
    Indra Talip <indra.talip@gmail.com> 2012
    mikespook 2012
    nansenat16 <nansenat16@null.tw> 2012
    Philip Jameson <philip.j@hostdime.com> 2012
    Raoul Thill <raoul.thill@gmail.com> 2012
    Stefan Engel <mail@engel-stefan.de> 2012
    Tony Bussieres <t.bussieres@gmail.com> 2012
    Vincent Caron <vcaron@bearstech.com> 2012
    Vincent Duvert <vincent@duvert.net> 2012
    Vladislav Poluhin <nuklea@gmail.com> 2012
    Zachary Auclair <zach101@gmail.com> 2012
    Ankit Solanki <ankit.solanki@gmail.com> 2011
    Dmitri Kuznetsov 2011
    Jared Bunting <jared.bunting@peachjean.com> 2011
    Jason Harris <jason@jasonfharris.com> 2011
    Les Peabody <lpeabody@gmail.com> 2011
    Liad Shani <liadff@gmail.com> 2011
    Lorenzo M. Catucci <lorenzo@sancho.ccd.uniroma2.it> 2011
    Matt Zuba <matt.zuba@goodwillaz.org> 2011
    Nicolas VINOT <aeris@imirhil.fr> 2011
    Shawn K. O'Shea <shawn@eth0.net> 2011
    Thayne Harbaugh <thayne@fusionio.com> 2011
    Łukasz Balcerzak <lukaszbalcerzak@gmail.com> 2010
    Andrew Kesterson <andrew@aklabs.net>
    cejones
    David A. Sjøen <david.sjoen@westcon.no>
    James Rhodes <jrhodes@redpointsoftware.com.au>
    Jonas Oberschweiber <jonas.oberschweiber@d-velop.de>
    larikale
    RhodeCode GmbH
    Sebastian Kreutzberger <sebastian@rhodecode.com>
    Steve Romanow <slestak989@gmail.com>
    SteveCohen
    Thomas <thomas@rhodecode.com>
    Thomas Waldmann <tw-public@gmx.de>