CVE-2024-41671: Twisted Web Information Disclosure Flaw

CVE-2024-41671 Overview

CVE-2024-41671 is an HTTP Request Smuggling vulnerability affecting Twisted, an event-based framework for internet applications supporting Python 3.6+. The HTTP 1.0 and 1.1 server provided by twisted.web could process pipelined HTTP requests out-of-order, potentially resulting in information disclosure. This vulnerability allows attackers to manipulate request processing sequences, leading to responses being sent to the wrong clients.

Critical Impact

Remote attackers can exploit out-of-order HTTP pipeline processing to intercept responses intended for other users, leading to information disclosure across client sessions.

Affected Products

• Twisted versions prior to 24.7.0rc1
• Applications using twisted.web HTTP server components
• Python 3.6+ environments running vulnerable Twisted installations

Discovery Timeline

• 2024-07-29 - CVE CVE-2024-41671 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2024-41671

Vulnerability Analysis

This vulnerability is classified under CWE-444 (Inconsistent Interpretation of HTTP Requests), commonly known as HTTP Request Smuggling. The flaw exists in how twisted.web handles HTTP pipelining, a feature that allows clients to send multiple HTTP requests over a single TCP connection without waiting for responses.

The core issue lies in the server's improper handling of chunked transfer encoding and trailer headers, which can cause the server to process pipelined requests out of their intended order. When requests are processed out-of-order, responses may be delivered to incorrect clients, exposing sensitive data from one session to another user.

The vulnerability affects network-accessible services with no privileges required for exploitation. No user interaction is necessary, meaning attacks can be fully automated against exposed Twisted-based web services.

Root Cause

The root cause stems from improper bounds checking in the chunked transfer encoding parser within src/twisted/web/http.py. The original implementation checked trailer header size limits at the wrong point in the parsing process, leading to inconsistent state when processing pipelined requests. Additionally, URL handling in src/twisted/web/_template_util.py lacked proper escaping, contributing to the vulnerability's exploitability.

Attack Vector

The attack vector is network-based, targeting HTTP 1.0/1.1 servers built with Twisted. An attacker sends specially crafted pipelined HTTP requests with manipulated chunked encoding or trailer headers. The server's improper parsing causes request boundaries to be misinterpreted, resulting in:

1. Response desynchronization between clients
2. Information leakage from one client's response to another
3. Potential session data exposure in multi-tenant environments

The security patches address these issues by implementing proper escape handling and correcting the trailer header size validation logic:

# Patch for src/twisted/web/_template_util.py
# Source: https://github.com/twisted/twisted/commit/046a164f89a0f08d3239ecebd750360f8914df33
    </body>
</html>
""" % {
-        b"url": URL
+        b"url": escape(URL.decode("utf-8")).encode("utf-8")
    }
    return content

# Patch for src/twisted/web/http.py - Chunked encoding trailer handling
# Source: https://github.com/twisted/twisted/commit/4a930de12fb67e88fefcb8822104152f42b27abc
        @returns: C{False}, as there is either insufficient data to continue,
            or no data remains.
        """
-        if (
-            self._receivedTrailerHeadersSize + len(self._buffer)
-            > self._maxTrailerHeadersSize
-        ):
-            raise _MalformedChunkedDataError("Trailer headers data is too long.")
-
        eolIndex = self._buffer.find(b"\r\n", self._start)

        if eolIndex == -1:
            # Still no end of network line marker found.
+            #
+            # Check if we've run up against the trailer size limit: if the next
+            # read contains the terminating CRLF then we'll have this many bytes
+            # of trailers (including the CRLFs).
+            minTrailerSize = (
+                self._receivedTrailerHeadersSize
+                + len(self._buffer)
+                + (1 if self._buffer.endswith(b"\r") else 2)
+            )
+            if minTrailerSize > self._maxTrailerHeadersSize:
+                raise _MalformedChunkedDataError("Trailer headers data is too long.")
            # Continue processing more data.
            return False

Detection Methods for CVE-2024-41671

Indicators of Compromise

• Unusual patterns in HTTP response timing where responses appear out-of-order
• Log entries showing mismatched request-response pairs or session identifiers
• Anomalous chunked transfer encoding requests with oversized trailer headers
• Evidence of users receiving data or sessions belonging to other users

Detection Strategies

• Monitor HTTP traffic for malformed chunked encoding requests with abnormal trailer sizes
• Implement deep packet inspection rules to detect HTTP request smuggling patterns
• Deploy SentinelOne Singularity platform to identify anomalous network behavior targeting web services
• Audit application logs for request-response desynchronization indicators

Monitoring Recommendations

• Enable verbose logging on Twisted-based HTTP servers to capture request processing order
• Configure network monitoring to alert on unusual pipelined HTTP request patterns
• Implement real-time analysis of HTTP traffic using SentinelOne's behavioral AI engine
• Set up alerts for _MalformedChunkedDataError exceptions in application logs

How to Mitigate CVE-2024-41671

Immediate Actions Required

• Upgrade Twisted to version 24.7.0rc1 or later immediately
• Review and audit all applications using twisted.web HTTP server components
• Implement network-level filtering to block suspicious chunked encoding patterns
• Consider disabling HTTP pipelining if not required for your application

Patch Information

The vulnerability is fixed in Twisted version 24.7.0rc1. Security patches are available through the official Twisted GitHub repository. Two key commits address the vulnerability:

• Commit 046a164 - URL escaping fix in template utilities
• Commit 4a930de - Chunked encoding trailer header validation fix

For detailed vulnerability information, see the GitHub Security Advisory GHSA-c8m8-j448-xjx7. Debian users should reference the Debian LTS Announcement for distribution-specific patches.

Workarounds

• Deploy a reverse proxy (nginx, HAProxy) in front of Twisted servers to normalize HTTP requests
• Implement request validation middleware to reject malformed chunked encoding
• Limit or disable HTTP pipelining support if business requirements permit
• Use Web Application Firewall (WAF) rules to detect and block HTTP smuggling attempts

# Configuration example - Upgrade Twisted to patched version
pip install --upgrade twisted>=24.7.0rc1

# Verify installed version
python -c "import twisted; print(twisted.__version__)"