high
7.5
CWE
444
Advisory Published
CVE Published
Advisory Published
Updated

CVE-2019-16786: HTTP Request Smuggling: Invalid Transfer-Encoding in Waitress

First published: Fri Dec 20 2019(Updated: )

### 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: pylons-project-security@googlegroups.com (if security related)

Credit: security-advisories@github.com security-advisories@github.com

Affected SoftwareAffected VersionHow to fix
pip/waitress<1.4.0
1.4.0
redhat/waitress<1.4.0
1.4.0
redhat/python-waitress<0:1.4.2-1.el8
0:1.4.2-1.el8
Agendaless Waitress<1.3.1
Oracle Communications Cloud Native Core Network Function Cloud Native Environment=1.10.0
Debian Debian Linux=9.0
Fedoraproject Fedora=30
Fedoraproject Fedora=31
Redhat Openstack=15
debian/waitress
1.2.0~b2-2+deb10u1
1.4.4-1.1+deb11u1
2.1.2-2

Remedy

https://github.com/Pylons/waitress/commit/f11093a6b3240fc26830b6111e826128af7771c3

Remedy

https://www.oracle.com/security-alerts/cpuapr2022.html

Never miss a vulnerability like this again

Sign up to SecAlerts for real-time vulnerability data matched to your software, aggregated from hundreds of sources.

Read MoreStart Free Trial

Reference Links

Parent vulnerabilities

(Appears in the following advisories)

Frequently Asked Questions

  • What is CVE-2019-16786?

    CVE-2019-16786 is a vulnerability that affects Waitress through version 1.3.1.

  • What is the impact of CVE-2019-16786?

    The impact of CVE-2019-16786 is that Waitress would parse the Transfer-Encoding header and only look for a single string value instead of a comma separated list as required by the HTTP standard.

  • How can CVE-2019-16786 be exploited?

    CVE-2019-16786 can be exploited by sending a malicious Transfer-Encoding header that does not contain the 'chunked' value.

  • What is the severity of CVE-2019-16786?

    The severity of CVE-2019-16786 is high with a severity value of 7.

  • How can I fix CVE-2019-16786?

    To fix CVE-2019-16786, upgrade Waitress to version 1.4.0 or later.

Company

Resources

Contact

SecAlerts Pty Ltd.
132 Wickham Terrace
Fortitude Valley,
QLD 4006, Australia
info@secalerts.co
By using SecAlerts services, you agree to our services end-user license agreement. This website is safeguarded by reCAPTCHA and governed by the Google Privacy Policy and Terms of Service. All names, logos, and brands of products are owned by their respective owners, and any usage of these names, logos, and brands for identification purposes only does not imply endorsement. If you possess any content that requires removal, please get in touch with us.
© 2025 SecAlerts Pty Ltd.
ABN: 70 645 966 203, ACN: 645 966 203