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Comments (6)

sc0tfree avatar sc0tfree commented on May 18, 2024 1

@justinsteven curious to hear your thoughts. And thanks so much for your contributions!

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sc0tfree avatar sc0tfree commented on May 18, 2024 1

I think this is because I'm using os.path.commonprefix instead of os.path.commonpath. Interesting edge case. Thanks!

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sc0tfree avatar sc0tfree commented on May 18, 2024

Thanks so much for finding this. I believe that there's no case where path should be blank, which should be a simple addition to

updog/updog/__main__.py

Line 132 in 5566289

if not is_valid_subpath(path, base_directory):

Any other thoughts on this?

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sc0tfree avatar sc0tfree commented on May 18, 2024

Verified fix. Going to commit.

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justinsteven avatar justinsteven commented on May 18, 2024

Still vulnerable when path is . or ./ or probably other things :(

I think the right fix might be

updog/updog/__main__.py

Line 146 in 39d544a

full_path = os.path.join(path, filename)

It should be:

full_path = os.path.join(base_directory, path, filename)

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justinsteven avatar justinsteven commented on May 18, 2024

Looks good to me!

Just one last thing. While testing this patch I noticed something weird :( but barely exploitable

If base_directory is /home/justin/www then doing an upload with path being /home/justin/www_zzzz is deemed valid, and is attempted (I get a Python stacktrace because the www_zzzz directory doesn't exist). Basically, your use of os.path.commonpath can be confused by appending to the directory name itself.

% # This is fine
% curl http://127.0.0.1:9090/upload -F 'file=@/etc/issue' -F 'path=/home/justin/www'
127.0.0.1 - - [19/Feb/2020 14:05:05] "POST /upload HTTP/1.1" 302 -
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<title>Redirecting...</title>
<h1>Redirecting...</h1>
<p>You should be redirected automatically to target URL: <a href=""></a>.  If not click the link.

% # This is weird
% curl http://127.0.0.1:9090/upload -F 'file=@/etc/issue' -F 'path=/home/justin/www_zzzz'
[2020-02-19 14:05:12,333] ERROR in app: Exception on /upload [POST]
Traceback (most recent call last):
  File "/home/justin/.local/lib/python3.7/site-packages/flask/app.py", line 2446, in wsgi_app
    response = self.full_dispatch_request()
  File "/home/justin/.local/lib/python3.7/site-packages/flask/app.py", line 1951, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/home/justin/.local/lib/python3.7/site-packages/flask/app.py", line 1820, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/home/justin/.local/lib/python3.7/site-packages/flask/_compat.py", line 39, in reraise
    raise value
  File "/home/justin/.local/lib/python3.7/site-packages/flask/app.py", line 1949, in full_dispatch_request
    rv = self.dispatch_request()
  File "/home/justin/.local/lib/python3.7/site-packages/flask/app.py", line 1935, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/home/justin/.local/lib/python3.7/site-packages/flask_httpauth.py", line 105, in decorated
    return f(*args, **kwargs)
  File "/home/justin/.local/lib/python3.7/site-packages/updog/__main__.py", line 149, in upload
    file.save(full_path)
  File "/home/justin/.local/lib/python3.7/site-packages/werkzeug/datastructures.py", line 3064, in save
    dst = open(dst, "wb")
FileNotFoundError: [Errno 2] No such file or directory: '/home/justin/www_zzzz/issue'
127.0.0.1 - - [19/Feb/2020 14:05:12] "POST /upload HTTP/1.1" 500 -
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<title>500 Internal Server Error</title>
<h1>Internal Server Error</h1>
<p>The server encountered an internal error and was unable to complete your request. Either the server is overloaded or there is an error in the application.</p>

Happy to help!

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