CVE-2020-28476 (https://snyk.io/vuln/SNYK-PYTHON-TORNADO-1017109): All versions of package tornado are vulnerable to Web Cache Poisoning 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. Seems to me like this CVE text is accurate, so we're waiting for upstream.
I don't see a public bug report on Tornado bug tracker, at least while using the 'obvious' search terms.
I think it might be https://github.com/tornadoweb/tornado/issues/2790.
This was deemed "not a vulnerability" according to the Snyk link...
