How severe is GHSA-m5ff-3wj3-8ph4?

No CVSS score has been assigned to GHSA-m5ff-3wj3-8ph4 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by GHSA-m5ff-3wj3-8ph4?

GHSA-m5ff-3wj3-8ph4 affects the following packages: waitress (PyPI). Ecosystems affected: PyPI.

How do I fix GHSA-m5ff-3wj3-8ph4?

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.

How do I detect GHSA-m5ff-3wj3-8ph4 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 GHSA-m5ff-3wj3-8ph4 if there is no patch (or I can't update yet)?

Assume what was exposed is already known: rotate any credential, token or key that the affected component could return, restrict the endpoint to callers that genuinely need it, and strip sensitive fields from responses and error output at the boundary rather than relying on the client not to read them.

Is GHSA-m5ff-3wj3-8ph4 actively exploited in the wild?

No public exploit code has been indexed for GHSA-m5ff-3wj3-8ph4 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.

When was GHSA-m5ff-3wj3-8ph4 published, and has it been updated?

GHSA-m5ff-3wj3-8ph4 was published on December 26, 2019 and was last updated on February 17, 2025. 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

HTTP Request Smuggling: Invalid whitespace characters in headers in WaitressGHSA-m5ff-3wj3-8ph4

Fix: Pylons/waitress@11d9e13

GHSA-m5ff-3wj3-8ph4 is a security vulnerability in waitress. A fix is available for waitress — see the affected versions and patch details below.

Published

Dec 26, 2019

Updated

Feb 17, 2025

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Feb 17, 2025 · OSV.dev, FIRST.org (EPSS)

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

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

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`waitress`	all versions	1.4.1`pip install --upgrade 'waitress==1.4.1'`

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 1.4.1 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
Assume what was exposed is already known: rotate any credential, token or key that the affected component could return, restrict the endpoint to callers that genuinely need it, and strip sensitive fields from responses and error output at the boundary rather than relying on the client not to read them.

Frequently Asked Questions

### 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

O3 Security · Impact-Aware SCA

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