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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)
<script>alert("It's a trap!");</script>
2) Escaped for insertion into HTML element or attribute context
>>> print h.escape(s)
<script>alert("It's a trap!");</script>
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.
| author | Søren Løvborg <sorenl@unity3d.com> |
|---|---|
| date | Tue, 28 Feb 2017 17:19:00 +0100 |
| parents | ed2fb6e84a02 |
| children | 2c3d30095d5e |
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.. _general: ======================= General Kallithea usage ======================= Repository deletion ------------------- Currently when an admin or owner deletes a repository, Kallithea does not physically delete said repository from the filesystem, but instead renames it in a special way so that it is not possible to push, clone or access the repository. There is a special command for cleaning up such archived repositories:: paster cleanup-repos --older-than=30d my.ini This command scans for archived repositories that are older than 30 days, displays them, and asks if you want to delete them (unless given the ``--dont-ask`` flag). If you host a large amount of repositories with forks that are constantly being deleted, it is recommended that you run this command via crontab. It is worth noting that even if someone is given administrative access to Kallithea and deletes a repository, you can easily restore such an action by renaming the repository directory, removing the ``rm__<date>`` prefix. File view: follow current branch -------------------------------- In the file view, left and right arrows allow to jump to the previous and next revision. Depending on the way revisions were created in the repository, this could jump to a different branch. When the checkbox ``Follow current branch`` is checked, these arrows will only jump to revisions on the same branch as the currently visible revision. So for example, if someone is viewing files in the ``beta`` branch and marks the `Follow current branch` checkbox, the < and > arrows will only show revisions on the ``beta`` branch. Changelog features ------------------ The core feature of a repository's ``changelog`` page is to show the revisions in a repository. However, there are several other features available from the changelog. Branch filter By default, the changelog shows revisions from all branches in the repository. Use the branch filter to restrict to a given branch. Viewing a changeset A particular changeset can be opened by clicking on either the changeset hash or the commit message, or by ticking the checkbox and clicking the ``Show selected changeset`` button at the top. Viewing all changes between two changesets To get a list of all changesets between two selected changesets, along with the changes in each one of them, tick the checkboxes of the first and last changeset in the desired range and click the ``Show selected changesets`` button at the top. You can only show the range between the first and last checkbox (no cherry-picking). From that page, you can proceed to viewing the overall delta between the selected changesets, by clicking the ``Compare revisions`` button. Creating a pull request You can create a new pull request for the changes of a particular changeset (and its ancestors) by selecting it and clicking the ``Open new pull request for selected changesets`` button. Permanent repository URLs ------------------------- Due to the complicated nature of repository grouping, URLs of repositories can often change. For example, a repository originally accessible from:: http://kallithea.example.com/repo_name would get a new URL after moving it to test_group:: http://kallithea.example.com/test_group/repo_name Such moving of a repository to a group can be an issue for build systems and other scripts where the repository paths are hardcoded. To mitigate this, Kallithea provides permanent URLs using the repository ID prefixed with an underscore. In all Kallithea URLs, for example those for the changelog and the file view, a repository name can be replaced by this ``_ID`` string. Since IDs are always the same, moving the repository to a different group will not affect such URLs. In the example, the repository could also be accessible as:: http://kallithea.example.com/_<ID> The ID of a given repository can be shown from the repository ``Summary`` page, by selecting the ``Show by ID`` button next to ``Clone URL``. Email notifications ------------------- With email settings properly configured in the Kallithea configuration file, Kallithea will send emails on user registration and when errors occur. Emails are also sent for comments on changesets. In this case, an email is sent to the committer of the changeset (if known to Kallithea), to all reviewers of the pull request (if applicable) and to all people mentioned in the comment using @mention notation. Trending source files --------------------- Trending source files are calculated based on a predefined dictionary of known types and extensions. If an extension is missing or you would like to scan custom files, it is possible to extend the ``LANGUAGES_EXTENSIONS_MAP`` dictionary located in ``kallithea/config/conf.py`` with new types. Cloning remote repositories --------------------------- Kallithea has the ability to clone repositories from given remote locations. Currently it supports the following options: - hg -> hg clone - svn -> hg clone - git -> git clone .. note:: svn -> hg cloning requires the ``hgsubversion`` library to be installed. If you need to clone repositories that are protected via basic authentication, you can pass the credentials in the URL, e.g. ``http://user:passw@remote.example.com/repo``. Kallithea will then try to login and clone using the given credentials. Please note that the given credentials will be stored as plaintext inside the database. However, the authentication information will not be shown in the clone URL on the summary page. Specific features configurable in the Admin settings ---------------------------------------------------- In general, the Admin settings should be self-explanatory and will not be described in more detail in this documentation. However, there are a few features that merit further explanation. Repository extra fields ^^^^^^^^^^^^^^^^^^^^^^^ In the *Visual* tab, there is an option "Use repository extra fields", which allows to set custom fields for each repository in the system. Once enabled site-wide, the custom fields can be edited per-repository under *Options* | *Settings* | *Extra Fields*. Example usage of such fields would be to define company-specific information into repositories, e.g., defining a ``repo_manager`` key that would give info about a manager of each repository. There's no limit for adding custom fields. Newly created fields are accessible via the API. Meta tagging ^^^^^^^^^^^^ In the *Visual* tab, option "Stylify recognised meta tags" will cause Kallithea to turn certain text fragments in repository and repository group descriptions into colored tags. Currently recognised tags are:: [featured] [stale] [dead] [lang => lang] [license => License] [requires => Repo] [recommends => Repo] [see => URI]