CVE-2021-23336

Published: 15 February 2021

The package python/cpython from 0 and before 3.6.13, from 3.7.0 and before 3.7.10, from 3.8.0 and before 3.8.8, from 3.9.0 and before 3.9.2 are vulnerable to Web Cache Poisoning via urllib.parse.parse_qsl and urllib.parse.parse_qs by using a vector called parameter cloaking. When the attacker can separate query parameters using a semicolon (;), they can cause a difference in the interpretation of the request between the proxy (running with default configuration) and the server. This can result in malicious requests being cached as completely safe ones, as the proxy would usually not see the semicolon as a separator, and therefore would not include it in a cache key of an unkeyed parameter.

Notes

fixing this in stable releases will break compatibility with
existing applications. Marking as low priority. We may decide
not to fix this at all in stable releases in the future.

Decided not to fix. The proposed fixes could possibly
break existing python packages in Ubuntu. There are
known regressions to this CVE, such as:
https://giters.com/scrapy/w3lib/issues/164

Status

Severity score breakdown

References

• https://github.com/python/cpython/pull/24297
• https://github.com/python/cpython/commit/fcbe0cb04d35189401c0c880ebfb4311e952d776 (master)
• https://snyk.io/blog/cache-poisoning-in-popular-open-source-packages/
• https://snyk.io/vuln/SNYK-UPSTREAM-PYTHONCPYTHON-1074933
• https://www.djangoproject.com/weblog/2021/feb/19/security-releases/
• https://ubuntu.com/security/notices/USN-4742-1
• https://www.cve.org/CVERecord?id=CVE-2021-23336
• NVD
• Launchpad
• Debian

Bugs

• https://bugs.python.org/issue42967