GHSA-PCG2-G6CJ-Q92C Tornado: Quadratic CPU usage when parsing HTTP headers with line folding

Summary Tornado's HTTP header parser takes quadratic time On² when a header value is continued across many "obsolete line folding" obs-fold lines. An unauthenticated attacker can send a request whose header block is mostly short continuation lines. Parsing it uses a large amount of CPU on the...