CVE-2019-16789
HIGHCVE-2019-16789 is a high-severity (CVSS 8.2) CWE-444 vulnerability in waitress. O3 Security confirms whether CVE-2019-16789 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
HTTP Request Smuggling in Waitress: Invalid whitespace characters in headers (Follow-up)
Blast Radius
waitressReal-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
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | waitress | all versions | 1.4.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for waitress. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update waitress to 1.4.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2019-16789 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.
How O3 protects you
O3 pinpoints whether CVE-2019-16789 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2019-16789. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2019-16789 in your dependencies?
O3 detects CVE-2019-16789 across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.