Due to a known but unfixed bug in the Python standard library’s
urllib.parse module (CVE-2015-2104), a crafted URL could bypass the
validation in the previous patch and still achieve an open redirect.
https://bugs.python.org/issue23505
Switch to using django.utils.http.is_safe_url, which already contains
a workaround for this bug.
Signed-off-by: Anders Kaseorg <anders@zulipchat.com>
This closes an open redirect vulnerability, one case of which was
found by Graham Bleaney and Ibrahim Mohamed using Pysa.
Signed-off-by: Anders Kaseorg <anders@zulipchat.com>
This endpoint serves requests which might originate from an image
preview link which had an http url and the message holding the image
link was rendered before we introduced thumbnailing. In that case
we would have used a camo proxy to proxy http content over https and
avoid mix content warnings.
In near future, we plan to drop use of camo and just rely on thumbor
to serve such images. This endpoint helps maintain backward
compatibility for links which were already rendered.
We used to add sharpen filter for all the image sizes whereas it was
intended for resized images only which would have been smoothened
out a bit by the resize operation.
This unnecessary use of the filter used to result in weird issues
with full size images.
For example: Image located at this url:-
http://arqex.com/wp-content/uploads/2015/02/trees.png
When rendered in full size would have just boundaries visible.
We seemed to have been doing too much of sharpening on the thumbnails.
The purpose of sharpening here was to just counter the softening
effects of a resize on an image but overdoing it is bad.
Value sharpen(0.5,0.2,true) seems to look good for achieving the
best results here on different displays as revealed in the manual
hit and trial based testing.
Thanks to @borisyankov for pointing out the issue and suggesting
the values.
This is a prepartory commit for the upcoming changes. It was meaningful
to extract this one out because this function is essentially a condition
check on whether a given url is one of the user_uploads or an external
one. Based on its value we decide whether a url must be thumbnailed or
not and thus this function will also be used in an upcoming commit
patching lib/thumbnail.py to do the same check before thumbnail url
generation.
In this commit we fix a bug due to which url preview images for urls
to custom emojis, realm icons or user avatars appeared broken when
such urls would be part of a Zulip message.
This is a preparatory commit to fix a bug in which a user posts
a link of custom emoji, user avatar or realm icon in a Zulip
message.
In this commit we are just adjusting the url generation in the
backend to have the '/user_uploads/' in the encrypted url generated
which the user is supposed to be redirected to and therefore
essentially reaching thumbor with the encrypted url.
This is necessary because 'user_uploads' and 'user_avatars' (or any
other item under 'user_avatars' endpoint) have a different folder
location under the local file storage backend. 'user_uploads'
endpoint's stuff is stored in a 'files' directory whereas stuff
'user_avatars' endpoint's stuff is stored in a 'avatars' directory.
Thumbor needs to know from which directory a particular local file
needs to be retrieved and therefore the zthumbor/loaders.py adds
a prefix location for the directory.
Since in an upcoming commit we are going to add user_avatars
directory location 'avatars' folder as a prefix this preparatory
commit helps simply doing the changes.
Various pieces of our thumbor-based thumbnailing system were already
merged; this adds the remaining pieces required for it to work:
* a THUMBOR_URL Django setting that controls whether thumbor is
enabled on the Zulip server (and if so, where thumbor is hosted).
* Replaces the overly complicated prototype cryptography logic
* Adds a /thumbnail endpoint (supported both on web and mobile) for
accessing thumbnails in messages, designed to support hosting both
external URLs as well as uploaded files (and applying Zulip's
security model for access to thumbnails of uploaded files).
* Modifies bugdown to, when THUMBOR_URL is set, render images with the
`src` attribute pointing /thumbnail (to provide a small thumbnail
for the image), along with adding a "data-original" attribute that
can be used to access the "original/full" size version of the image.
There are a few things that don't work quite yet:
* The S3 backend support is incomplete and doesn't work yet.
* The error pages for unauthorized access are ugly.
* We might want to rename data-original and /thumbnail?size=original
to use some other name, like "full", that better reflects the fact
that we're potentially not serving the original image URL.
Mateusz Mandera
Anders Kaseorg
Aditya Bansal
Tim Abbott
