[2.7] bpo-35907: Avoid file reading as disallowing the unnecessary URL scheme in urllib (GH-11842) #11842

push0ebp · 2019-02-13T17:11:03Z

https://bugs.python.org/issue35907

…me in urllib

the-knights-who-say-ni · 2019-02-13T17:11:19Z

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tomashek · 2019-04-08T17:38:04Z

Is this patch the accepted resolution for CVE-2019-9948? If so, when is it expected to be merged?

Misc/NEWS.d/next/Library/2019-02-13-17-21-10.bpo-35907.ckk2zg.rst

Lib/test/test_urllib.py

tiran · 2019-05-13T14:56:22Z

Lib/urllib.py

+
+        # bpo-35907: # disallow the file reading with the type not allowed
+        if not hasattr(self, name) or \
+            (self == _urlopener and name == 'open_local_file'):


Please simplify the fix. There is no need to check for _urlopener here. Just block all access to local_file:// schema. We don't need special cases for subclasses or special instances.

If it does not check the instance type of self, all of overridden open_local_file method will be blocked.
will be okay?
like this

self.assertRaises(IOError, DummyURLopener().open 'local_file://example') self.assertRaises(IOError, DummyURLopener().open 'local-file://example')

I think that it needs to check open_local_file is overridden.
What do you think?

I think it has to expect this test result.

def test_local_file_open(self): class DummyURLopener(urllib.URLopener): def open_local_file(self, url): return url class DummyURLopener2(urllib.URLopener): def open_test(self, url): return url opener = DummyURLopener() opener2 = DummyURLopener2() for url in ('local-file://example', 'local_file://example'): self.assertEqual(opener.open(url), '//example') self.assertRaises(IOError, urllib.urlopen, url) self.assertRaises(IOError, opener2.open, url) self.assertEqual(opener2.open('test://example'), '//example')

but Considering the overriding method and instance type check was complex.
If you have a better idea. let me know.

bedevere-bot · 2019-05-13T14:56:32Z

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

Add prefix "CVE-2019-9948: "

…sies in DummyURLopener test, and simplify mitigation

push0ebp

I have made the requested changes; please review again.

Lib/test/test_urllib.py

Misc/NEWS.d/next/Library/2019-02-13-17-21-10.bpo-35907.ckk2zg.rst

push0ebp · 2019-05-16T17:10:53Z

Lib/urllib.py

+
+        # bpo-35907: # disallow the file reading with the type not allowed
+        if not hasattr(self, name) or \
+            (self == _urlopener and name == 'open_local_file'):


If it does not check the instance type of self, all of overridden open_local_file method will be blocked.
will be okay?
like this

self.assertRaises(IOError, DummyURLopener().open 'local_file://example') self.assertRaises(IOError, DummyURLopener().open 'local-file://example')

I think that it needs to check open_local_file is overridden.
What do you think?

push0ebp · 2019-05-16T17:50:29Z

Lib/urllib.py

+
+        # bpo-35907: # disallow the file reading with the type not allowed
+        if not hasattr(self, name) or \
+            (self == _urlopener and name == 'open_local_file'):


I think it has to expect this test result.

def test_local_file_open(self): class DummyURLopener(urllib.URLopener): def open_local_file(self, url): return url class DummyURLopener2(urllib.URLopener): def open_test(self, url): return url opener = DummyURLopener() opener2 = DummyURLopener2() for url in ('local-file://example', 'local_file://example'): self.assertEqual(opener.open(url), '//example') self.assertRaises(IOError, urllib.urlopen, url) self.assertRaises(IOError, opener2.open, url) self.assertEqual(opener2.open('test://example'), '//example')

but Considering the overriding method and instance type check was complex.
If you have a better idea. let me know.

vstinner · 2019-05-20T15:01:08Z

Lib/urllib.py

+
+        # bpo-35907: # disallow the file reading with the type not allowed
+        if not hasattr(self, name) or \
+            getattr(self, name) == self.open_local_file:


Another fix is to rename the open_local_file() as _open_local_file(). But... In Python 2.7, there is a risk that the method is called directly in 3rd party code for whatever reason :-(

Why do you compare function objects instead of simply name == "open_local_file"?

@tiran
If someone rename open_local_file() method and also forgets to modify name == "open_local_file", it may be bypassed.
So I made the mitigation compare the object to raise syntax error.
Should I do change back?

I concur with Christian, please test directly the name, remove getattr().

@vstinner
I agree with you. I also considered renaming the open_local_file(). I think that this fix can guarantees availability to the developers who want to override this method. But I chose another fix to minimize side effects for third party codes.

Please remove getattr().

Yes. I will do it. I want suggest you other fix.

if not hasattr(self, name): if proxy: return self.open_unknown_proxy(proxy, fullurl, data) else: return self.open_unknown(fullurl, data) if name == 'open_local_file': raise IOError, ('url error', 'invalid url type', urltype) try:

I think that it is better to raise exception with explicit error message for developers to overriding open_local_file().
they can easily recognize local_file is invalid type.
What do you think about it?
or should I use open_unknown()?

if not hasattr(self, name) or \ name == 'open_local_file':

# bpo-35907: disallow the file reading with the type not allowed if not hasattr(self, name) or name == 'open_local_file': ...

LGTM.

if name == 'open_local_file': raise IOError, ('url error', 'invalid url type', urltype)

That's wrong exception type, don't do that.

I have changed it. Please review.

I have made the requested changes; please review again.

vstinner

LGTM.

Modify the object to string in check method name.

vstinner

LGTM. Just curious about the # which looks like a typo.

vstinner · 2019-05-21T17:26:37Z

Lib/urllib.py

@@ -203,7 +203,9 @@ def open(self, fullurl, data=None):
        name = 'open_' + urltype
        self.type = urltype
        name = name.replace('-', '_')
-        if not hasattr(self, name):
+
+        # bpo-35907: # disallow the file reading with the type not allowed


I don't understand the # in "# bpo-35907: # disallow ...". Is it a typo?

Oh Sorry, my mistake. I will correct it.

I have fixed the typo.

Fix typo

vstinner · 2019-05-21T21:12:32Z

Thanks @push0ebp for the fix!

push0ebp · 2019-05-22T03:20:22Z

Thank you for your accept.
related to #13474

bpo-35907: Avoid file reading as disallowing the unnecessary URL sche…

8f99cc7

…me in urllib

bedevere-bot added the awaiting review label Feb 13, 2019

the-knights-who-say-ni added the CLA not signed label Feb 13, 2019

📜🤖 Added by blurb_it.

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push0ebp changed the title ~~bpo-35907: Avoid file reading as disallowing the unnecessary URL scheme in urllib~~ [2.7] bpo-35907: Avoid file reading as disallowing the unnecessary URL scheme in urllib (GH-11842) Feb 13, 2019

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push0ebp added 2 commits May 17, 2019 02:31

Update 2019-02-13-17-21-10.bpo-35907.ckk2zg.rst

f20a31c

Add prefix "CVE-2019-9948: "

Update test_urllib.py and urllib.py\nchange assertEqual into assertRa…

179a5f7

…sies in DummyURLopener test, and simplify mitigation

push0ebp commented May 19, 2019

View reviewed changes

csabella requested a review from tiran May 19, 2019 11:13

vstinner reviewed May 20, 2019

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bedevere-bot added awaiting merge and removed awaiting changes labels May 20, 2019

Update urllib.py

3cda03c

Modify the object to string in check method name.

vstinner approved these changes May 21, 2019

View reviewed changes

Update urllib.py

8b7d7ab

Fix typo

vstinner merged commit b15bde8 into python:2.7 May 21, 2019

bedevere-bot removed the awaiting merge label May 21, 2019

vstinner mentioned this pull request May 21, 2019

bpo-35907, CVE-2019-9948: urllib rejects local_file:// scheme #13474

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[2.7] bpo-35907: Avoid file reading as disallowing the unnecessary URL scheme in urllib (GH-11842) #11842

[2.7] bpo-35907: Avoid file reading as disallowing the unnecessary URL scheme in urllib (GH-11842) #11842

push0ebp commented Feb 13, 2019 •

edited

the-knights-who-say-ni commented Feb 13, 2019

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push0ebp commented May 22, 2019

[2.7] bpo-35907: Avoid file reading as disallowing the unnecessary URL scheme in urllib (GH-11842) #11842

[2.7] bpo-35907: Avoid file reading as disallowing the unnecessary URL scheme in urllib (GH-11842) #11842

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push0ebp commented Feb 13, 2019 • edited

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vstinner commented May 21, 2019

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push0ebp commented Feb 13, 2019 •

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