GHSA-g2xc-35jw-c63p
HIGHGHSA-g2xc-35jw-c63p is a high-severity (CVSS 7.1) CWE-444 vulnerability in waitress. O3 Security confirms whether GHSA-g2xc-35jw-c63p is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
HTTP Request Smuggling: Invalid Transfer-Encoding in Waitress
Blast Radius
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Description
Impact
Waitress would parse the Transfer-Encoding header and only look for a single string value, if that value was not chunked it would fall through and use the Content-Length header instead.
According to the HTTP standard Transfer-Encoding should be a comma separated list, with the inner-most encoding first, followed by any further transfer codings, ending with chunked.
Requests sent with:
Transfer-Encoding: gzip, chunked
Would incorrectly get ignored, and the request would use a Content-Length header instead to determine the body size of the HTTP message.
This could allow for Waitress to treat a single request as multiple requests in the case of 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.
Waitress will now return a 501 Not Implemented error if the Transfer-Encoding is not chunked or contains multiple elements. Waitress does not support any transfer codings such as gzip or deflate.
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
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | waitress | all versions | 1.4.0 |
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 1.4.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-g2xc-35jw-c63p 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-g2xc-35jw-c63p 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-g2xc-35jw-c63p. 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-g2xc-35jw-c63p in your dependencies?
O3 detects GHSA-g2xc-35jw-c63p across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.