Wsgiserver 02 Cpython 3104 Exploit May 2026
An attacker sends a request to the vulnerable Python server with a crafted header like this:
GET / HTTP/1.1
Host: vulnerable-server.com
X-Malicious-Header: value\r\nSet-Cookie: session=attacker_owned\r\nContent-Length: 0\r\n\r\n
Because wsgiref fails to sanitize the \r\n sequence inside the header value, the server might interpret the rest of the string as a new HTTP response or request headers. This allows for:
The vulnerability exists in the implementation of the WSGIServer class within the wsgiref library. The library is a reference implementation of the WSGI specification and is intended for development purposes, though it is sometimes used in lightweight production deployments. wsgiserver 02 cpython 3104 exploit
The core issue lies in how the server handles HTTP request headers.
The version tag 02 likely refers to an early iteration of CherryPy’s WSGI server from the mid-2000s. That server was: An attacker sends a request to the vulnerable
If you find any production system running wsgiserver 02 with CPython 3.10.4, you have a security incident waiting to happen. The exploitability is high because attackers can often cause:
WSGI servers must correctly parse Content-Length and Transfer-Encoding headers. An exploit might craft conflicting headers, causing the WSGI server and a frontend proxy (like Nginx) to desynchronize. This could allow an attacker to “smuggle” a second request past security checks. Because wsgiref fails to sanitize the \r\n sequence
Example (hypothetical):
Sending a request with both Content-Length and Transfer-Encoding: chunked in a specific order could cause the older wsgiserver to treat the message differently than a reverse proxy.
Mitigation:
Use a well-maintained WSGI server (e.g., Waitress v2.1+, Gunicorn v20.1+). Avoid custom or legacy versions of wsgiserver.
If you manage a Python 3.10.4 web application, follow these hardening steps:
| Action | Tool / Command |
|--------|----------------|
| Identify your WSGI server | pip list | grep -i "gunicorn\|uwsgi\|waitress\|cherrypy\|cheroot" |
| Upgrade from legacy wsgiserver | Replace with cheroot (the modern fork) or gunicorn |
| Enable HTTP parsing strictness | gunicorn --strict or waitress --strict-http |
| Set header limits | --limit-request-line 8190 --limit-request-fields 100 |
| Run as non-root user | useradd -r wsgi-user |
| Use a reverse proxy (Nginx) with request validation | proxy_request_buffering on; proxy_set_header Host $host; |
| Deploy a WAF (Web Application Firewall) | libmodsecurity for Nginx |
| Regular vulnerability scanning | safety check or pip-audit |
An attacker sends a request to the vulnerable Python server with a crafted header like this:
GET / HTTP/1.1
Host: vulnerable-server.com
X-Malicious-Header: value\r\nSet-Cookie: session=attacker_owned\r\nContent-Length: 0\r\n\r\n
Because wsgiref fails to sanitize the \r\n sequence inside the header value, the server might interpret the rest of the string as a new HTTP response or request headers. This allows for:
The vulnerability exists in the implementation of the WSGIServer class within the wsgiref library. The library is a reference implementation of the WSGI specification and is intended for development purposes, though it is sometimes used in lightweight production deployments.
The core issue lies in how the server handles HTTP request headers.
The version tag 02 likely refers to an early iteration of CherryPy’s WSGI server from the mid-2000s. That server was:
If you find any production system running wsgiserver 02 with CPython 3.10.4, you have a security incident waiting to happen. The exploitability is high because attackers can often cause:
WSGI servers must correctly parse Content-Length and Transfer-Encoding headers. An exploit might craft conflicting headers, causing the WSGI server and a frontend proxy (like Nginx) to desynchronize. This could allow an attacker to “smuggle” a second request past security checks.
Example (hypothetical):
Sending a request with both Content-Length and Transfer-Encoding: chunked in a specific order could cause the older wsgiserver to treat the message differently than a reverse proxy.
Mitigation:
Use a well-maintained WSGI server (e.g., Waitress v2.1+, Gunicorn v20.1+). Avoid custom or legacy versions of wsgiserver.
If you manage a Python 3.10.4 web application, follow these hardening steps:
| Action | Tool / Command |
|--------|----------------|
| Identify your WSGI server | pip list | grep -i "gunicorn\|uwsgi\|waitress\|cherrypy\|cheroot" |
| Upgrade from legacy wsgiserver | Replace with cheroot (the modern fork) or gunicorn |
| Enable HTTP parsing strictness | gunicorn --strict or waitress --strict-http |
| Set header limits | --limit-request-line 8190 --limit-request-fields 100 |
| Run as non-root user | useradd -r wsgi-user |
| Use a reverse proxy (Nginx) with request validation | proxy_request_buffering on; proxy_set_header Host $host; |
| Deploy a WAF (Web Application Firewall) | libmodsecurity for Nginx |
| Regular vulnerability scanning | safety check or pip-audit |
