Affected versions of this package are vulnerable to Web Cache Poisoning via
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.
GET /?q=legitimate&utm_content=1;q=malicious HTTP/1.1 Host: example.com Upgrade-Insecure-Requests: 1 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.83 Safari/537.36 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,imag e/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9 Accept-Encoding: gzip, deflate Accept-Language: en-US,en;q=0.9 Connection: close
The server sees 3 parameters here:
utm_content and then
q again. On the other hand, the proxy considers this full string:
1;q=malicious as the value of
utm_content, which is why the cache key would only contain
python/cpython to version 3.6.13, 3.7.10, 3.8.8, 3.9.2 or higher.