Apache Tomcat 10.0.0-M1 to 10.0.6, 9.0.0.M1 to 9.0.46 and 8.5.0 to 8.5.66 did not correctly parse the HTTP transfer-encoding request header in some circumstances leading to the possibility to request smuggling when used with a reverse proxy. Specifically: - Tomcat incorrectly ignored the transfer encoding header if the client declared it would only accept an HTTP/1.0 response; - Tomcat honoured the identify encoding; and - Tomcat did not ensure that, if present, the chunked encoding was the final encoding.

In JetBrains Ktor before 1.4.3, HTTP Request Smuggling was possible.

aiohttp is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.10.11, the Python parser parses newlines in chunk extensions incorrectly which can lead to request smuggling vulnerabilities under certain conditions. If a pure Python version of aiohttp is installed (i.e. without the usual C extensions) or `AIOHTTP_NO_EXTENSIONS` is enabled, then an attacker may be able to execute a request smuggling attack to bypass certain firewalls or proxy protections. Version 3.10.11 fixes the issue.

reel through 0.6.1 allows Request Smuggling attacks due to incorrect Content-Length and Transfer encoding header parsing. It is possible to conduct HTTP request smuggling attacks by sending the Content-Length header twice. Furthermore, invalid Transfer Encoding headers were found to be parsed as valid which could be leveraged for TE:CL smuggling attacks. Note: This project is deprecated, and is not maintained any more.

Netty 4.1.43.Final allows HTTP Request Smuggling because it mishandles Transfer-Encoding whitespace (such as a [space]Transfer-Encoding:chunked line) and a later Content-Length header. This issue exists because of an incomplete fix for CVE-2019-16869.

In Ktor before 1.3.0, request smuggling is possible when running behind a proxy that doesn't handle Content-Length and Transfer-Encoding properly or doesn't handle \n as a headers separator.