Описание
Regular Expression Denial of Service (REDoS) in httplib2
Impact
A malicious server which responds with long series of \xa0 characters in the www-authenticate header may cause Denial of Service (CPU burn while parsing header) of the httplib2 client accessing said server.
Patches
Version 0.19.0 contains new implementation of auth headers parsing, using pyparsing library. https://github.com/httplib2/httplib2/pull/182
Workarounds
Technical Details
The vulnerable regular expression is https://github.com/httplib2/httplib2/blob/595e248d0958c00e83cb28f136a2a54772772b50/python3/httplib2/__init__.py#L336-L338
The section before the equals sign contains multiple overlapping groups. Ignoring the optional part containing a comma, we have:
Since all three infinitely repeating groups accept the non-breaking space character \xa0, a long string of \xa0 causes catastrophic backtracking.
The complexity is cubic, so doubling the length of the malicious string of \xa0 makes processing take 8 times as long.
Reproduction Steps
Run a malicious server which responds with
but with many more \xa0 characters.
An example malicious python server is below:
Connect to the server with httplib2:
To benchmark performance with shorter strings, you can set the path to a number e.g. http://localhost:1337/1000
References
Thanks to Ben Caller (Doyensec) for finding vulnerability and discrete notification.
For more information
If you have any questions or comments about this advisory:
- Open an issue in httplib2
- Email current maintainer at 2021-01
Ссылки
- https://github.com/httplib2/httplib2/security/advisories/GHSA-93xj-8mrv-444m
- https://nvd.nist.gov/vuln/detail/CVE-2021-21240
- https://github.com/httplib2/httplib2/pull/182
- https://github.com/httplib2/httplib2/commit/bd9ee252c8f099608019709e22c0d705e98d26bc
- https://github.com/pypa/advisory-database/tree/main/vulns/httplib2/PYSEC-2021-16.yaml
- https://pypi.org/project/httplib2
Пакеты
httplib2
< 0.19.0
0.19.0
Связанные уязвимости
httplib2 is a comprehensive HTTP client library for Python. In httplib2 before version 0.19.0, a malicious server which responds with long series of "\xa0" characters in the "www-authenticate" header may cause Denial of Service (CPU burn while parsing header) of the httplib2 client accessing said server. This is fixed in version 0.19.0 which contains a new implementation of auth headers parsing using the pyparsing library.
httplib2 is a comprehensive HTTP client library for Python. In httplib2 before version 0.19.0, a malicious server which responds with long series of "\xa0" characters in the "www-authenticate" header may cause Denial of Service (CPU burn while parsing header) of the httplib2 client accessing said server. This is fixed in version 0.19.0 which contains a new implementation of auth headers parsing using the pyparsing library.
httplib2 is a comprehensive HTTP client library for Python. In httplib2 before version 0.19.0, a malicious server which responds with long series of "\xa0" characters in the "www-authenticate" header may cause Denial of Service (CPU burn while parsing header) of the httplib2 client accessing said server. This is fixed in version 0.19.0 which contains a new implementation of auth headers parsing using the pyparsing library.
httplib2 is a comprehensive HTTP client library for Python. In httplib ...
Уязвимость клиентской библиотеки HTTP httplib2, связанная с некотролируемым расходом ресурсов, позволяющая нарушителю вызвать отказ в обслуживании