[Django] #25905: Unsafe usage of urljoin() within FileStorageSystem
Django
------------------------------+---------------------------
Reporter: free-Runner | Owner: nobody
Type: Bug | Status: new
Component: Core (Other) | Version: 1.9
Severity: Normal | Keywords: file, storage
Triage Stage: Unreviewed | Has patch: 1
Easy pickings: 0 | UI/UX: 0
------------------------------+---------------------------
It may be possible to override the hostname when displaying a link to a
static/media file with an attacker-controlled filename. The url() method
in FileStorageSystem uses urljoin(base,url) to combine the base_url
(typically STATIC_URL or MEDIA_URL) to the filename. The urljoin function
has an edge case where if the url parameter starts with "//", the base_url
value is overwritten. Thus, if an attacker can set the name variable of a
FileStorageSystem instance to "//www.evil.com", any url method call on
that instance will return an external link pointing to the attacker's
site. Creating a file of the name "\\www.evil.com" is also acceptable as
the filepath_to_uri function (that is called on the filename before the
urljoin call) converts all backslashes to forward-slashes. The latter
example works better as it is a completely valid Linux file name.
This issue can't be exploited using framework-provided upload techniques
(FileFields, ImageFields, etc) as they properly escape the filename.
However, an application may directly initialize a FileStorageSystem using
user-controlled data or allow users to modify the name attribute of an
existing FileStorageSystem instance. In such cases, an attacker could
convert the expected relative paths into absolute external URLs.
This issue can simply be patched by modifying the line found
here[https://github.com/django/django/blob/master/django/core/files/storage.py#L302]
as follows:
return urljoin(self.base_url,
filepath_to_uri(get_valid_filename(name)))
This change filters the filename provided through the get_valid_filename
function from django.utils.text. This function does a sufficient of
eliminating the ability to override the base_url.
Note: This issue was initially disclosed to the Django security team and
was decided not to be treated as a security issue, but instead a bug.
--
Ticket URL: <https://code.djangoproject.com/ticket/25905>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
Django
Reporter: free-Runner | Owner: nobody
Type: Bug | Status: new
Component: Core (Other) | Version: 1.9
Keywords: file, storage | Triage Stage: Unreviewed
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
Changes (by free-Runner):
* cc: aman.ali@… (added)
* needs_better_patch: => 0
* needs_tests: => 0
* needs_docs: => 0
Old description:
New description:
It may be possible to override the hostname when displaying a link to a
static/media file with an attacker-controlled filename. The url() method
in FileStorageSystem uses urljoin(base,url) to combine the base_url
(typically STATIC_URL or MEDIA_URL) to the filename. The urljoin function
has an edge case where if the url parameter starts with "//", the base_url
value is overwritten. Thus, if an attacker can set the name variable of a
FileStorageSystem instance to "//www.evil.com", any url method call on
that instance will return an external link pointing to the attacker's
site. Creating a file of the name "\\www.evil.com" is also acceptable as
the filepath_to_uri function (that is called on the filename before the
urljoin call) converts all backslashes to forward-slashes. The latter
example works better as it is a completely valid Linux file name.
This issue can't be exploited using framework-provided upload techniques
(FileFields, ImageFields, etc) as they properly escape the filename.
However, an application may directly initialize a FileStorageSystem using
user-controlled data or allow users to modify the name attribute of an
existing FileStorageSystem instance. In such cases, an attacker could
convert the expected relative paths into absolute external URLs.
This issue can simply be patched by modifying the line found
here[https://github.com/django/django/blob/master/django/core/files/storage.py#L302]
as follows:
return urljoin(self.base_url,
filepath_to_uri(get_valid_filename(name)))
This change filters the filename provided through the get_valid_filename
function from django.utils.text. This function does a sufficient job of
eliminating the ability to override the base_url.
Note: This issue was initially disclosed to the Django security team and
was decided not to be treated as a security issue, but instead a bug.
--
--
Ticket URL: <https://code.djangoproject.com/ticket/25905#comment:1>
Django
Reporter: free-Runner | Owner: nobody
Type: Cleanup/optimization | Status: new
Component: File uploads/storage | Version: 1.9
Severity: Normal | Resolution:
Keywords: file, storage | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Changes (by timgraham):
* type: Bug => Cleanup/optimization
* component: Core (Other) => File uploads/storage
* stage: Unreviewed => Accepted
--
Ticket URL: <https://code.djangoproject.com/ticket/25905#comment:2>
Django
Reporter: free-Runner | Owner: nobody
Type: Cleanup/optimization | Status: new
Component: File uploads/storage | Version: 1.9
Severity: Normal | Resolution:
Keywords: file, storage | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Description changed by free-Runner:
Old description:
> function from django.utils.text. This function does a sufficient job of
> eliminating the ability to override the base_url.
>
> Note: This issue was initially disclosed to the Django security team and
> was decided not to be treated as a security issue, but instead a bug.
New description:
It may be possible to override the hostname when displaying a link to a
static/media file with an attacker-controlled filename. The url() method
in FileStorageSystem uses urljoin(base,url) to combine the base_url
(typically STATIC_URL or MEDIA_URL) to the filename. The urljoin function
has an edge case where if the url parameter starts with {{{"//"}}}, the
base_url value is overwritten. Thus, if an attacker can set the name
variable of a FileStorageSystem instance to {{{"//www.evil.com"}}}, any
url method call on that instance will return an external link pointing to
the attacker's site. Creating a file of the name {{{"\\www.evil.com"}}} is
also acceptable as the filepath_to_uri function (that is called on the
filename before the urljoin call) converts all backslashes to forward-
slashes. The latter example works better as it is a completely valid Linux
file name.
This issue can't be exploited using framework-provided upload techniques
(FileFields, ImageFields, etc) as they properly escape the filename.
However, an application may directly initialize a FileStorageSystem using
user-controlled data or allow users to modify the name attribute of an
existing FileStorageSystem instance. In such cases, an attacker could
convert the expected relative paths into absolute external URLs.
This issue can simply be patched by modifying the line found
here[https://github.com/django/django/blob/master/django/core/files/storage.py#L302]
as follows:
{{{return urljoin(self.base_url,
filepath_to_uri(name).replace('//','/'))}}}
This change filters the filename provided through the get_valid_filename
function from django.utils.text. This function does a sufficient job of
eliminating the ability to override the base_url.
Note: This issue was initially disclosed to the Django security team and
was decided not to be treated as a security issue, but instead a bug.
--
--
Ticket URL: <https://code.djangoproject.com/ticket/25905#comment:3>
Django
Reporter: free-Runner | Owner: nobody
Type: Cleanup/optimization | Status: new
Component: File uploads/storage | Version: 1.9
Severity: Normal | Resolution:
Keywords: file, storage | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Easy pickings: 0 | UI/UX: 0
Changes (by timgraham):
* needs_tests: 0 => 1
Comment:
A test is also needed. If you could send a pull request after adding that,
it's easiest for review purposes.
--
Ticket URL: <https://code.djangoproject.com/ticket/25905#comment:4>
Django
Reporter: free-Runner | Owner: rixx
Type: Cleanup/optimization | Status: assigned
Component: File uploads/storage | Version: 1.9
Severity: Normal | Resolution:
Keywords: file, storage | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Changes (by rixx):
* owner: nobody => rixx
* status: new => assigned
* needs_tests: 1 => 0
--
Ticket URL: <https://code.djangoproject.com/ticket/25905#comment:5>
Django
Reporter: free-Runner | Owner: rixx
Component: File uploads/storage | Version: 1.9
Keywords: file, storage | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Changes (by Russell Keith-Magee <russell@…>):
* status: assigned => closed
* resolution: => fixed
Comment:
In [changeset:"fdf5cd3429369954e8deb764d9f30f6374581613" fdf5cd34]:
{{{
#!CommitTicketReference repository=""
revision="fdf5cd3429369954e8deb764d9f30f6374581613"
Fixed #25905 -- Prevented leading slashes in urljoin() calls
Leading slashes in the second urljoin argument will return exactly that
argument, breaking FileSystemStorage.url behavior if called with a
parameter with leading slashes.
Also added test cases for null bytes and None. Thanks to Markus for
help and review.
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/25905#comment:6>
Django
Reporter: Aman Ali | Owner: Tobias
Type: | Kunze
Cleanup/optimization | Status: closed
Component: File | Version: 1.9
uploads/storage |
Severity: Normal | Resolution: fixed
Keywords: file, storage | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Changes (by bhch):
* cc: bhch (added)
Comment:
The
[https://github.com/django/django/commit/fdf5cd3429369954e8deb764d9f30f6374581613
#diff-87c0869f58253f571c08ccf0fc5c7465R410 current fix] strips off all the
leading slashes thereby making it a relative path, to which `urljoin`
later prepends a base url. This removes the possibility of serving a
default file from the static url.
I think a better solution would be to remove more than 1 leading slashes,
but not one.
Current implementation: `url.lstrip('/')`.
Proposed: `re.sub(r'/{2,}', '/', url)`.
This will allow us to serve a default file from static url.
--
Ticket URL: <https://code.djangoproject.com/ticket/25905#comment:7>
Django
Reporter: Aman Ali | Owner: Tobias
Type: | Kunze
Cleanup/optimization | Status: closed
Component: File | Version: 1.9
uploads/storage |
Severity: Normal | Resolution: fixed
Keywords: file, storage | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Comment (by Tobias Kunze):
Thank you for your feedback – as this ticket has been closed some time
ago, the best way forward would be to open a new ticket. There you could
describe the behaviour you would like to see as opposed to the current
one, and reference this ticket as introducing current behaviour. A new
ticket will run through the proper ticket lifecycle and (more importantly)
will get the attention of other developers.
--
Ticket URL: <https://code.djangoproject.com/ticket/25905#comment:8>