title: 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.
problem types: CWE-444 Inconsistent Interpretation of HTTP Requests ('HTTP Request Smuggling')
affected:
{
product: Waitress
vendor: Pylons
versions:
lessThan: 1.4.1, status: affected, version: < 1.4.1, versionType: custom
}
metrics:
cvssV3_1: [
attackComplexity: HIGH
attackVector: NETWORK
availabilityImpact: NONE
baseScore: 7.1
baseSeverity: HIGH
confidentialityImpact: LOW
integrityImpact: HIGH
privilegesRequired: LOW
scope: CHANGED
userInteraction: NONE
vectorString: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:L/I:H/A:N
version: 3.1
]
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.