In Twisted Web through 19.10.0, there was an HTTP request splitting vulnerability. When presented with two content-length headers, it ignored the first header. When the second content-length value was set to zero, the request body was interpreted as a pipelined request.
https://www.oracle.com/security-alerts/cpuoct2020.html
https://usn.ubuntu.com/4308-2/
https://usn.ubuntu.com/4308-1/
https://security.gentoo.org/glsa/202007-24
https://lists.debian.org/debian-lts-announce/2022/02/msg00021.html
https://know.bishopfox.com/advisories/twisted-version-19.10.0