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GHSA-fh3h-vg37-cc95
No affected components available
Impact
When WebOb normalizes the HTTP Location header to include the request hostname, it does so by parsing the URL that the user is to be redirected to with Python's urllib.parse, and joining it to the base URL. urlsplit (called internally by urljoin) however treats a // at the start of a string as a URI without a scheme, and then treats the next part as the hostname. urljoin will then use that hostname from the second part as the hostname replacing the original one from the request.
In a previous advisory https://github.com/Pylons/webob/security/advisories/GHSA-mg3v-6m49-jhp3 an attempt to fix this was made by forcing the replacement of // with /%2f, however this did not take into account that since Python 3.10 urlsplit internally strips ASCII tab, carriage return, and newline characters from the string, so /\t/attacker.com gets turned into //attacker.com and the attacker is able to bypass the changes introduced in that previous advisory, thereby bringing back the problem that was attempted to be fixed.
>>> parse.urlparse("//attacker.com/some/path")
ParseResult(scheme='', netloc='attacker.com', path='/some/path', params='', query='', fragment='')
WebOb uses urljoin to take the request URI and join the redirect location to it, so assuming the request URI is https://example.org/ and the URL to redirect to is /\t/attacker.com/some/path/:
>>> parse.urljoin("https://example.org/", "/\t/attacker.com/some/path/")
'https://attacker.com/some/path/'
Which redirects from example.org where we want the user to stay to attacker.com.
Patches
This issue has been fixed in WebOb 1.8.10.
Workarounds
Any use of the Response class that includes a location can be rewritten to make sure to always pass a full URI that includes the hostname to redirect the user to, or to validate that the redirect target starts with a scheme (e.g. http:// or https://) before assigning to Response.location.
References
- https://github.com/Pylons/webob/security/advisories/GHSA-mg3v-6m49-jhp3
- CVE-2024-42353
Thanks
- Caleb Brown of Google
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. The attacker needs the user to perform some action, like clicking a link. The vulnerability can affect other systems as well, not just the initial system. There is a low impact on the confidentiality of the information. There is a low impact on the integrity of the data.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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