{"cve":"CVE-2019-16786","nvd":{"published":"2019-12-20T23:15:11.277","modified":"2026-06-17T02:22:48.190","status":"Modified","description":"Waitress through version 1.3.1 would parse the Transfer-Encoding header and only look for a single string value, if that value was not chunked it would fall through and use the Content-Length header instead. 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. Requests sent with: \"Transfer-Encoding: gzip, chunked\" would incorrectly get ignored, and the request would use a Content-Length header instead to determine the body size of the HTTP message. This could allow for Waitress to treat a single request as multiple requests in the case of HTTP pipelining. This issue is fixed in Waitress 1.4.0.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","score":7.5},"cwes":["CWE-444"],"references":["https://access.redhat.com/errata/RHSA-2020:0720","https://docs.pylonsproject.org/projects/waitress/en/latest/#security-fixes","https://github.com/Pylons/waitress/commit/f11093a6b3240fc26830b6111e826128af7771c3","https://github.com/Pylons/waitress/security/advisories/GHSA-g2xc-35jw-c63p","https://lists.debian.org/debian-lts-announce/2022/05/msg00011.html"],"products":["agendaless:waitress","debian:debian_linux","fedoraproject:fedora","oracle:communications_cloud_native_core_network_function_cloud_native_environment","redhat:openstack"],"source":"nvd","synced_at":"2026-10-19T20:59:27.069234358+00:00"},"epss":{"cve":"CVE-2019-16786","score":0.02379,"percentile":0.8389,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-g2xc-35jw-c63p","url":"https://osv.dev/vulnerability/GHSA-g2xc-35jw-c63p","summary":"HTTP Request Smuggling: Invalid Transfer-Encoding in Waitress","modified":"2026-07-08T05:59:57.212266307Z","packages":[{"ecosystem":"PyPI","name":"waitress","purl":"pkg:pypi/waitress","ranges":["<1.4.0"],"fixed":["1.4.0"]}]},{"id":"PYSEC-2019-137","url":"https://osv.dev/vulnerability/PYSEC-2019-137","summary":"","modified":"2023-11-08T04:01:21.705659Z","packages":[{"ecosystem":"PyPI","name":"waitress","purl":"pkg:pypi/waitress","ranges":["<1.3.1"],"fixed":["1.3.1"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}