HTTP Request Smuggling: Invalid Transfer-Encoding in Waitress
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, chunkedWould 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: pylons-project-security@googlegroups.com (if security related)
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | waitress | < 1.4.0 | 1.4.0 |
References
- https://github.com/Pylons/waitress/security/advisories/GHSA-g2xc-35jw-c63p
- https://github.com/Pylons/waitress/commit/f11093a6b3240fc26830b6111e826128af7771c3
- https://docs.pylonsproject.org/projects/waitress/en/latest/#security-fixes
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/GVDHR2DNKCNQ7YQXISJ45NT4IQDX3LJ7/
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/LYEOTGWJZVKPRXX2HBNVIYWCX73QYPM5/
- https://access.redhat.com/errata/RHSA-2020:0720
- https://nvd.nist.gov/vuln/detail/CVE-2019-16786
- https://github.com/Pylons/waitress
- https://github.com/pypa/advisory-database/tree/main/vulns/waitress/PYSEC-2019-137.yaml
- https://lists.debian.org/debian-lts-announce/2022/05/msg00011.html
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/GVDHR2DNKCNQ7YQXISJ45NT4IQDX3LJ7
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/LYEOTGWJZVKPRXX2HBNVIYWCX73QYPM5
- https://www.oracle.com/security-alerts/cpuapr2022.html
- CVSS vector
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:L/A:N- Weakness (CWE)
CWE-444- Platform
- Python (PyPI)
- Package
waitress- Disclosed
- 20.12.2019
- Updated
- 11.10.2026 13:19
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2019-137 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-g2xc-35jw-c63p - CC BY 4.0
Vulnerability history: waitress
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 10
- First → latest
- 12.2019 10.2024
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 2
- High 4
- Medium 4
Disclosures per year
- 2019: 5
- 2020: 1
- 2021: 0
- 2022: 2
- 2023: 0
- 2024: 2
- 2025: 0
- 2026: 0
-
HTTP Request Smuggling: Invalid Transfer-Encoding in Waitress this entry
Know which vulnerabilities affect your application
With the DockRay integration and software inventory enabled, DockRay checks reported component versions against known vulnerabilities and notifies you about confirmed matches. Coverage depends on the supported technology and available advisory data.