The refactoring present in Apache Tomcat 9.0.28 to 9.0.30, 8.5.48 to 8.5.50 and 7.0.98 to 7.0.99 introduced a regression. The result of the regression was that invalid Transfer-Encoding headers were incorrectly processed leading to a possibility of HTTP Request Smuggling if Tomcat was located behind a reverse proxy that incorrectly handled the invalid Transfer-Encoding header in a particular manner. Such a reverse proxy is considered unlikely.
Exploitability
AV:NAC:HPR:NUI:NScope
S:UImpact
C:LI:LA:N4.8/CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N