Eventlet versions prior to 0.40.3 contain a vulnerability in the WSGI parser that allows HTTP request smuggling via improper handling of HTTP trailer sections. This flaw can enable attackers to bypass front-end security controls, launch targeted attacks against users, and poison web caches. The issue is fixed in version 0.40.3 by dropping trailers, which may break setups relying on trailers. Avoid exposing eventlet.wsgi to untrusted clients as a workaround.