Inconsistent interpretation of HTTP requests in waitress - CVE-2019-16786

Detailed vulnerability description

The vulnerability allows a remote non-authenticated attacker to manipulate data.

Waitress through version 1.3.1 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. This issue is fixed in Waitress 1.4.0.

How to mitigate CVE-2019-16786

Sources

• https://access.redhat.com/errata/RHSA-2020:0720
• https://docs.pylonsproject.org/projects/waitress/en/latest/#security-fixes
• https://github.com/Pylons/waitress/commit/f11093a6b3240fc26830b6111e826128af7771c3
• https://github.com/Pylons/waitress/security/advisories/GHSA-g2xc-35jw-c63p
• 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/