{"id":"CVE-2019-16792","aliases":["GHSA-4ppp-gpcr-7qf6","GHSA-j7j6-7hfx-5522","PYSEC-2020-178"],"title":"HTTP Request Smuggling: Content-Length Sent Twice in Waitress","summary":"HTTP Request Smuggling: Content-Length Sent Twice in Waitress","severity":"critical","vendor":"waitress","product":"waitress","ecosystem":"pip","affected":["waitress < 1.4.0"],"patched":["waitress 1.4.0"],"published":"2019-12-20","updated":"2026-07-08","source":"OSV","sourceUrl":"https://osv.dev/vulnerability/GHSA-4ppp-gpcr-7qf6","references":[{"url":"https://github.com/Pylons/waitress/security/advisories/GHSA-4ppp-gpcr-7qf6"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2019-16792"},{"url":"https://github.com/Pylons/waitress/commit/575994cd42e83fd772a5f7ec98b2c56751bd3f65"},{"url":"https://docs.pylonsproject.org/projects/waitress/en/latest/#security-fixes"},{"url":"https://github.com/Pylons/waitress"},{"url":"https://github.com/pypa/advisory-database/tree/main/vulns/waitress/PYSEC-2020-178.yaml"},{"url":"https://lists.debian.org/debian-lts-announce/2022/05/msg00011.html"},{"url":"https://www.oracle.com/security-alerts/cpuapr2022.html"}],"tags":["osv","pip"],"epss":0.01984,"epssPercentile":0.79436,"ingestedAt":"2026-07-08T18:25:45.519Z","slug":"CVE-2019-16792","body":"## Overview\n\n### Impact\n\nWaitress would header fold a double `Content-Length` header and due to being unable to cast the now comma separated value to an integer would set the `Content-Length` to 0 internally.\n\nSo a request with:\n\n```\nContent-Length: 10\nContent-Length: 10\n```\n\nwould get transformed to:\n\n```\nContent-Length: 10, 10\n```\n\nWhich would Waitress would then internally set to `Content-Lenght: 0`.\n\nWaitress would then treat the request as having no body, thereby treating the body of the request as a new request in HTTP pipelining.\n\n### Patches\n\nThis issue is fixed in Waitress 1.4.0. This brings a range of changes to harden Waitress against potential HTTP request confusions, and may change the behaviour of Waitress behind non-conformist proxies. \n\nThe Pylons Project recommends upgrading as soon as possible, while validating that the changes in Waitress don't cause any changes in behavior.\n\n### Workarounds\n\nVarious reverse proxies may have protections against sending potentially bad HTTP requests to the backend, and or hardening against potential issues like this. If the reverse proxy doesn't use HTTP/1.1 for connecting to the backend issues are also somewhat mitigated, as HTTP pipelining does not exist in HTTP/1.0 and Waitress will close the connection after every single request (unless the Keep Alive header is explicitly sent... so this is not a fool proof security method).\n\n### Issues/more security issues:\n\n* open an issue at https://github.com/Pylons/waitress/issues (if not sensitive or security related)\n* email the Pylons Security mailing list: pylons-project-security@googlegroups.com (if security related)\n\n## Affected packages\n\n- `waitress < 1.4.0`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `waitress 1.4.0`","depth":"midnight","depthScore":53,"depthScoreParts":{"impact":52.3,"likelihood":0.4,"exploitation":0,"ransomware":0},"changes":[]}