GHSA-4f7p-27jc-3c36 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.
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-4f7p-27jc-3c36.
EPSS Exploitation Probability
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
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
When using Waitress behind a proxy that does not properly validate the incoming HTTP request matches the RFC7230 standard, Waitress and the frontend proxy may disagree on where one request starts and where it ends.
This would allow requests to be smuggled via the front-end proxy to waitress and later behavior.
There are two classes of vulnerability that may lead to request smuggling that are addressed by this advisory:
- The use of Python's
int()to parse strings into integers, leading to+10to be parsed as10, or0x01to be parsed as1, where as the standard specifies that the string should contain only digits or hex digits. - Waitress does not support chunk extensions, however it was discarding them without validating that they did not contain illegal characters
Patches
This has been fixed in Waitress 2.1.1
Workarounds
When deploying a proxy in front of waitress, turning on any and all functionality to make sure that the request matches the RFC7230 standard. Certain proxy servers may not have this functionality though and users are encouraged to upgrade to the latest version of waitress instead.
References
For more information
If you have any questions or comments about this advisory:
- Open an issue in the Github issue tracker (if not security related/sensitive)
- Email us at [email protected] (If security related or sensitive)
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | waitress | all versions | 2.1.1pip install --upgrade 'waitress==2.1.1' |
Affected Products
waitressagendalessdebian linuxdebianDetection & mitigation playbook
Open-source dependencyDetect
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 2.1.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-4f7p-27jc-3c36 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.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat OpenStack Platform 13.0 - ELS | python-waitress-0:1.4.4-2.el7ost | RHSA-2022:1264 |
| Red Hat OpenStack Platform 16.1 | python-waitress-0:2.0.0-1.el8ost | RHSA-2022:1254 |
| Red Hat OpenStack Platform 16.2 | python-waitress-0:2.0.0-1.el8ost | RHSA-2022:1253 |
Frequently Asked Questions
Is GHSA-4f7p-27jc-3c36 in your dependencies?
Find it across PyPI, including transitive dependencies.