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.

# Makefile for Sphinx documentation
#

# You can set these variables from the command line.
SPHINXOPTS    =
SPHINXBUILD   = sphinx-build
PAPER         =
BUILDDIR      = _build

# Internal variables.
PAPEROPT_a4     = -D latex_paper_size=a4
PAPEROPT_letter = -D latex_paper_size=letter
ALLSPHINXOPTS   = -d $(BUILDDIR)/doctrees $(PAPEROPT_$(PAPER)) $(SPHINXOPTS) .

.PHONY: help clean html dirhtml singlehtml pickle json htmlhelp qthelp devhelp epub latex latexpdf text man changes linkcheck doctest

help:
	@echo "Please use \`make <target>' where <target> is one of"
	@echo "  html       to make standalone HTML files"
	@echo "  dirhtml    to make HTML files named index.html in directories"
	@echo "  singlehtml to make a single large HTML file"
	@echo "  pickle     to make pickle files"
	@echo "  json       to make JSON files"
	@echo "  htmlhelp   to make HTML files and a HTML help project"
	@echo "  qthelp     to make HTML files and a qthelp project"
	@echo "  devhelp    to make HTML files and a Devhelp project"
	@echo "  epub       to make an epub"
	@echo "  latex      to make LaTeX files, you can set PAPER=a4 or PAPER=letter"
	@echo "  latexpdf   to make LaTeX files and run them through pdflatex"
	@echo "  text       to make text files"
	@echo "  man        to make manual pages"
	@echo "  changes    to make an overview of all changed/added/deprecated items"
	@echo "  linkcheck  to check all external links for integrity"
	@echo "  doctest    to run all doctests embedded in the documentation (if enabled)"

clean:
	-rm -rf $(BUILDDIR)/*

html:
	$(SPHINXBUILD) -b html $(ALLSPHINXOPTS) $(BUILDDIR)/html
	@echo
	@echo "Build finished. The HTML pages are in $(BUILDDIR)/html."

dirhtml:
	$(SPHINXBUILD) -b dirhtml $(ALLSPHINXOPTS) $(BUILDDIR)/dirhtml
	@echo
	@echo "Build finished. The HTML pages are in $(BUILDDIR)/dirhtml."

singlehtml:
	$(SPHINXBUILD) -b singlehtml $(ALLSPHINXOPTS) $(BUILDDIR)/singlehtml
	@echo
	@echo "Build finished. The HTML page is in $(BUILDDIR)/singlehtml."

pickle:
	$(SPHINXBUILD) -b pickle $(ALLSPHINXOPTS) $(BUILDDIR)/pickle
	@echo
	@echo "Build finished; now you can process the pickle files."

json:
	$(SPHINXBUILD) -b json $(ALLSPHINXOPTS) $(BUILDDIR)/json
	@echo
	@echo "Build finished; now you can process the JSON files."

htmlhelp:
	$(SPHINXBUILD) -b htmlhelp $(ALLSPHINXOPTS) $(BUILDDIR)/htmlhelp
	@echo
	@echo "Build finished; now you can run HTML Help Workshop with the" \
	      ".hhp project file in $(BUILDDIR)/htmlhelp."

qthelp:
	$(SPHINXBUILD) -b qthelp $(ALLSPHINXOPTS) $(BUILDDIR)/qthelp
	@echo
	@echo "Build finished; now you can run "qcollectiongenerator" with the" \
	      ".qhcp project file in $(BUILDDIR)/qthelp, like this:"
	@echo "# qcollectiongenerator $(BUILDDIR)/qthelp/Kallithea.qhcp"
	@echo "To view the help file:"
	@echo "# assistant -collectionFile $(BUILDDIR)/qthelp/Kallithea.qhc"

devhelp:
	$(SPHINXBUILD) -b devhelp $(ALLSPHINXOPTS) $(BUILDDIR)/devhelp
	@echo
	@echo "Build finished."
	@echo "To view the help file:"
	@echo "# mkdir -p $$HOME/.local/share/devhelp/Kallithea"
	@echo "# ln -s $(BUILDDIR)/devhelp $$HOME/.local/share/devhelp/Kallithea"
	@echo "# devhelp"

epub:
	$(SPHINXBUILD) -b epub $(ALLSPHINXOPTS) $(BUILDDIR)/epub
	@echo
	@echo "Build finished. The epub file is in $(BUILDDIR)/epub."

latex:
	$(SPHINXBUILD) -b latex $(ALLSPHINXOPTS) $(BUILDDIR)/latex
	@echo
	@echo "Build finished; the LaTeX files are in $(BUILDDIR)/latex."
	@echo "Run \`make' in that directory to run these through (pdf)latex" \
	      "(use \`make latexpdf' here to do that automatically)."

latexpdf:
	$(SPHINXBUILD) -b latex $(ALLSPHINXOPTS) $(BUILDDIR)/latex
	@echo "Running LaTeX files through pdflatex..."
	make -C $(BUILDDIR)/latex all-pdf
	@echo "pdflatex finished; the PDF files are in $(BUILDDIR)/latex."

text:
	$(SPHINXBUILD) -b text $(ALLSPHINXOPTS) $(BUILDDIR)/text
	@echo
	@echo "Build finished. The text files are in $(BUILDDIR)/text."

man:
	$(SPHINXBUILD) -b man $(ALLSPHINXOPTS) $(BUILDDIR)/man
	@echo
	@echo "Build finished. The manual pages are in $(BUILDDIR)/man."

changes:
	$(SPHINXBUILD) -b changes $(ALLSPHINXOPTS) $(BUILDDIR)/changes
	@echo
	@echo "The overview file is in $(BUILDDIR)/changes."

linkcheck:
	$(SPHINXBUILD) -b linkcheck $(ALLSPHINXOPTS) $(BUILDDIR)/linkcheck
	@echo
	@echo "Link check complete; look for any errors in the above output " \
	      "or in $(BUILDDIR)/linkcheck/output.txt."

doctest:
	$(SPHINXBUILD) -b doctest $(ALLSPHINXOPTS) $(BUILDDIR)/doctest
	@echo "Testing of doctests in the sources finished, look at the " \
	      "results in $(BUILDDIR)/doctest/output.txt."