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

> Attackers can exploit HTTP request smuggling via LF/CRLF parsing discrepancies in Waitress, potentially bypassing security controls or accessing unauthorized data.

- **Severity:** High 7.1 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 20 Dec 2019
- **Updated:** 5 Aug 2024
- **Also known as:** DEBIAN-CVE-2019-16785, GHSA-pg36-wpm5-g57p, PYSEC-2019-136, UBUNTU-CVE-2019-16785

## What is CVE-2019-16785?

CVE-2019-16785 is a high-severity vulnerability in Debian Debian Linux, published on 20 Dec 2019. Any signed-in user can exploit it over the network, with no action from the victim.

### Official 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.

Weakness: CWE-444 (Inconsistent Interpretation of HTTP Requests)

## Which versions are affected by CVE-2019-16785?

3 open source packages ship an affected version, including waitress. It affects 5 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `waitress` | PyPI | All versions | 1.4.0 |
| `waitress` | PyPI | All versions | 1.4.0 |
| `waitress` | PyPI | All versions | 1.4.0 |

Products: Agendaless Waitress, Debian Debian Linux, Fedoraproject Fedora, Oracle Communications Cloud Native Core Network Function Cloud Native Environment, Redhat Openstack.

## How do I fix CVE-2019-16785?

Upgrade waitress to 1.4.0 or later.

## Is CVE-2019-16785 being exploited?

There is no known exploitation of CVE-2019-16785 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

- [CVE-2024-49768](https://insights.sbomify.com/CVE-2024-49768/): Waitress has request processing race condition in HTTP pipelining with invalid first request (critical 9.1)
- [CVE-2024-49769](https://insights.sbomify.com/CVE-2024-49769/): Waitress has a denial of service leading to high CPU usage/resource exhaustion (high 7.5)
- [CVE-2022-24761](https://insights.sbomify.com/CVE-2022-24761/): HTTP Request Smuggling in waitress (high 7.5)
- [CVE-2019-16792](https://insights.sbomify.com/CVE-2019-16792/): HTTP Request Smuggling: Content-Length Sent Twice in Waitress (high 7.1)
- [CVE-2019-16789](https://insights.sbomify.com/CVE-2019-16789/): HTTP Request Smuggling in Waitress: Invalid whitespace characters in headers (high 7.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2019-16785 and fix it if it is affected.

What it is: CVE-2019-16785 is a high-severity vulnerability in Debian Debian Linux, published on 20 Dec 2019. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2019-16785 in the wild and no public exploit code.

Affected packages and fixed versions:
- waitress (PyPI): affected all versions; fixed in 1.4.0
- waitress (PyPI): affected all versions; fixed in 1.4.0
- waitress (PyPI): affected all versions; fixed in 1.4.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2019-16785/ (Markdown: https://insights.sbomify.com/CVE-2019-16785/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2019-16785
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2019-16785
- OSV: https://osv.dev/vulnerability/CVE-2019-16785

---
From sbomify Insights: https://insights.sbomify.com/CVE-2019-16785/
Summaries are generated and may contain mistakes; the official description above is the record.