CVE-2019-16786

An HTTP-interpretation flaw was found in waitress which did not properly validate incoming HTTP headers. When parsing the Transfer-Encoding header, waitress would look only for a single string value. According to the HTTP standard, Transfer-Encoding should be a comma-separated list, with the inner-most encoding first, followed by any further transfer codings, ending with ‘chunked’. Because of this flaw, requests sent with: “Transfer-Encoding: gzip, chunked” would get ignored, and waitress would use the Content-Length header instead to determine the body size of the HTTP message. A remote attacker could exploit this flaw to force waitress to accept potentially bad HTTP requests or treat a single request as multiple requests in the case of HTTP pipelining.