[ python-Bugs-1546628 ] urlparse.urljoin odd behaviour

Tue Aug 29 13:29:43 CEST 2006

Bugs item #1546628, was opened at 2006-08-25 23:04
Message generated for change (Comment added) made by the_j10
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Category: Python Library
Group: Python 2.4
Status: Open
Resolution: None
Priority: 5
Submitted By: Andres Riancho (andresriancho)
Assigned to: Nobody/Anonymous (nobody)
Summary: urlparse.urljoin odd behaviour

Initial Comment:
Hi !

   I think i have found a bug on the urljoin function
of the urlparse
module. I'm using Python 2.4.3 (#2, Apr 27 2006,
14:43:58), [GCC 4.0.3
(Ubuntu 4.0.3-1ubuntu5)] on linux2 . Here is a demo of
the bug :

>>> import urlparse
>>>urlparse.urljoin('http://www.f00.com/','//a')
'http://a'
>>>
urlparse.urljoin('http://www.f00.com/','https://0000/somethingIsWrong')
'https://0000/somethingIsWrong'
>>>
urlparse.urljoin('http://www.f00.com/','https://0000/somethingIsWrong')
'https://0000/somethingIsWrong'
>>>
urlparse.urljoin('http://www.f00.com/','file:///etc/passwd')
'file:///etc/passwd'

   The result for the first call to urljoin should be
either
'http://www.f00.com/a' or 'http://www.f00.com//a'. The
result to the
second and third call to urljoin should be
'http://www.f00.com/', or maybe an
exception ?

   Please correct me if i'm wrong and this is some kind
of feature or
the bug was already reported. This bug can result in a
security vuln,
take this code as an example:

// viewImage.py //
import htmlTools                                      
    # Some fake
module, just for the example
import urlparse                                       
     # module
with bug.

htmlTools.startHtml()                                 
  # print <html>
params = htmlTools.getParams()                # get the
query string
parameters
htmlTools.printToHtml( '<img src=' + urlparse.urljoin(
'http://myWebsite/' , params['image'] ) + '>' )
htmlTools.endHtml()                                   
 # print </html>
// viewImage.py //

   The code should generate an html that shows an image
from the site
http://myWebsite/, but with the urljoin bug, the image
source can be
manipulated and result in a completely different html.

Cheers,

Andres Riancho

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Comment By: Andrew  Jones (the_j10)
Date: 2006-08-29 21:29

Message:
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user_id=332575

The second argument in the urljoin method can be either an 
absolute url or a relative url as specified by rfc1808. So
your 1st example: '//a' gives a relative position w.r.t the
base resulting in: 'http://a'. This is similar to how `cd
/boot` takes you to a path relative to the filesystem's root
'/'. 

In the rest of your examples you have the scheme name
'https'in the url as the 2nd argument. urljoin follows the
rfc1808 and accepts the second argument if it has a scheme
name as the absolute url and returns it.

This behavior is not very intuitive. Perhaps the urlparse 
could be extended to have a urlappend method, which has the 
behavior you expected. Hmmm...

-- Andrew

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