CVE-2019-16789

HTTP Request Smuggling in Waitress: Invalid whitespace characters in headers

Description

In Waitress through version 1.4.0, 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. Specially crafted requests containing special whitespace characters in the Transfer-Encoding header 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. This issue is fixed in Waitress 1.4.1 through more strict HTTP field validation.

Remediation

Workaround:

  • 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.

Category

7.1
CVSS
Severity: High
CVSS 3.1 •
CVSS 2.0 •
EPSS 0.35%
Vendor Advisory fedoraproject.org Vendor Advisory fedoraproject.org Vendor Advisory redhat.com Vendor Advisory pylonsproject.org
Affected: Pylons Waitress
Published at:
Updated at:

References

Link Tags
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/GVDHR2DNKCNQ7YQXISJ45NT4IQDX3LJ7/ vendor advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/LYEOTGWJZVKPRXX2HBNVIYWCX73QYPM5/ vendor advisory
https://access.redhat.com/errata/RHSA-2020:0720 third party advisory vendor advisory
https://www.oracle.com/security-alerts/cpuapr2022.html third party advisory patch
https://docs.pylonsproject.org/projects/waitress/en/latest/#security-fixes release notes vendor advisory
https://github.com/github/advisory-review/pull/14604 third party advisory broken link
https://github.com/Pylons/waitress/commit/11d9e138125ad46e951027184b13242a3c1de017 third party advisory patch
https://lists.debian.org/debian-lts-announce/2022/05/msg00011.html third party advisory mailing list

Frequently Asked Questions

What is the severity of CVE-2019-16789?
CVE-2019-16789 has been scored as a high severity vulnerability.
How to fix CVE-2019-16789?
As a workaround for remediating CVE-2019-16789: 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.
Is CVE-2019-16789 being actively exploited in the wild?
As for now, there are no information to confirm that CVE-2019-16789 is being actively exploited. According to its EPSS score, there is a ~0% probability that this vulnerability will be exploited by malicious actors in the next 30 days.
What software or system is affected by CVE-2019-16789?
CVE-2019-16789 affects Pylons Waitress.
This platform uses data from the NIST NVD, MITRE CVE, MITRE CWE, First.org and CISA KEV but is not endorsed or certified by these entities. CVE is a registred trademark of the MITRE Corporation and the authoritative source of CVE content is MITRE's CVE web site. CWE is a registred trademark of the MITRE Corporation and the authoritative source of CWE content is MITRE's CWE web site.
© 2025 Under My Watch. All Rights Reserved.