How severe is CVE-2019-16792?

CVE-2019-16792 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2019-16792?

CVE-2019-16792 affects the following packages: waitress (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2019-16792?

Update waitress to 1.4.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2019-16792 is resolved across your whole dependency graph.

How do I detect CVE-2019-16792 in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for waitress, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2019-16792 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2019-16792 actively exploited in the wild?

No public exploit code has been indexed for CVE-2019-16792 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2019-16792?

CVE-2019-16792 has an EPSS (Exploit Prediction Scoring System) score of 2.0%, placing it in the 81th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2019-16792?

CVE-2019-16792 is classified as CWE-444 (CWE-444). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2019-16792 published, and has it been updated?

CVE-2019-16792 was published on January 22, 2020 and was last updated on October 20, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍

🐍 PyPI

Not in CISA KEV

HIGH severity

CVE-2019-16792 — waitress

HIGHFix: Pylons/waitress@575994c

CVE-2019-16792 is a high-severity (CVSS 7.5) CWE-444 vulnerability in waitress. A fix is available for waitress — see the affected versions and patch details below.

HTTP Request Smuggling: Content-Length Sent Twice in Waitress

Also known asGHSA-4ppp-gpcr-7qf6 GHSA-j7j6-7hfx-5522PYSEC-2020-178

Published

Jan 22, 2020

Updated

Oct 20, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 5, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

2.0%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs81th percentile — riskier than 81% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

🐍waitress

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

Impact

Waitress 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.

So a request with:

Content-Length: 10
Content-Length: 10

would get transformed to:

Content-Length: 10, 10

Which would Waitress would then internally set to Content-Lenght: 0.

Waitress would then treat the request as having no body, thereby treating the body of the request as a new request in HTTP pipelining.

Patches

This 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.

The Pylons Project recommends upgrading as soon as possible, while validating that the changes in Waitress don't cause any changes in behavior.

Workarounds

Various 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).

Issues/more security issues:

open an issue at https://github.com/Pylons/waitress/issues (if not sensitive or security related)
email the Pylons Security mailing list: [email protected] (if security related)

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`waitress`	all versions	1.4.0`pip install --upgrade 'waitress==1.4.0'`

Affected Products

3 products · 3 configurations

Application

waitressagendaless

≤ 1.3.1

range

debian linuxdebian

1 version

9.0

Application

communications cloud native core network function cloud native environmentoracle

1 version

1.10.0

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for waitress, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update waitress to 1.4.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2019-16792 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

### Impact Waitress 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. So a request with: ``` Content-Length: 10 Content-Length: 10 ``` would get transformed to: ``` Content-Length: 10, 10 ``` Which would Waitress would then internally set to `Content-Lenght: 0`. Waitress would then treat the request as having no body, thereby treating the body of the request as a new request in HTTP pipelining. ### Patches This issue is fixed in Waitress 1.4.0. This brings a ran