GHSA-m5ff-3wj3-8ph4
GHSA-m5ff-3wj3-8ph4 is a security vulnerability in waitress. O3 Security confirms whether GHSA-m5ff-3wj3-8ph4 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
HTTP Request Smuggling: Invalid whitespace characters in headers in Waitress
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
Impact
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.
Content-Length: 10
Transfer-Encoding: [\x0b]chunked
For clarity:
0x0b == vertical tab
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.
Patches
Please upgrade to Waitress 1.4.1 which fixes this issue with stricter HTTP field validation.
Waitress 1.4.1 due to this change has become much more strict in what is allowed in header values, while the maintainers don't believe that these changes will cause any issues, it may cause failures with non-conformist reverse proxies or clients, and it is highly recommend that users validate the changes in their environment and make sure it won't cause any unacceptable failures.
Workarounds
You may enable additional protections on front-end servers, those that follow RFC7230 correctly would drop the request with a 400 Bad Request.
Waitress will now correctly responds to the request with a 400 Bad Request, and will drop the connection to avoid any potential HTTP pipelining issues.
References
This was mentioned in https://portswigger.net/research/http-desync-attacks-what-happened-next and was specifically mentioned as being an issue in HAProxy which did not properly filter it in this article: https://nathandavison.com/blog/haproxy-http-request-smuggling
Thanks
The Pylons Project would like to thank ZeddYu Lu for doing extended testing against Waitress 1.4.0 and bringing this to our attention!
For more information
If you have any questions or comments about this advisory:
- 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
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | waitress | all versions | 1.4.1 |
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 1.4.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-m5ff-3wj3-8ph4 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 GHSA-m5ff-3wj3-8ph4 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 GHSA-m5ff-3wj3-8ph4. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-m5ff-3wj3-8ph4 in your dependencies?
O3 detects GHSA-m5ff-3wj3-8ph4 across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.