CVE-2023-47641 in aiohttp
Summary
by MITRE • 11/14/2023
aiohttp is an asynchronous HTTP client/server framework for asyncio and Python. Affected versions of aiohttp have a security vulnerability regarding the inconsistent interpretation of the http protocol. HTTP/1.1 is a persistent protocol, if both Content-Length(CL) and Transfer-Encoding(TE) header values are present it can lead to incorrect interpretation of two entities that parse the HTTP and we can poison other sockets with this incorrect interpretation. A possible Proof-of-Concept (POC) would be a configuration with a reverse proxy(frontend) that accepts both CL and TE headers and aiohttp as backend. As aiohttp parses anything with chunked, we can pass a chunked123 as TE, the frontend entity will ignore this header and will parse Content-Length. The impact of this vulnerability is that it is possible to bypass any proxy rule, poisoning sockets to other users like passing Authentication Headers, also if it is present an Open Redirect an attacker could combine it to redirect random users to another website and log the request. This vulnerability has been addressed in release 3.8.0 of aiohttp. Users are advised to upgrade. There are no known workarounds for this vulnerability.
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Analysis
by VulDB Data Team • 02/04/2025
The vulnerability identified as CVE-2023-47641 affects the aiohttp asynchronous HTTP client/server framework for Python, specifically targeting the inconsistent interpretation of HTTP protocol headers. This security flaw stems from how the framework handles the presence of both Content-Length and Transfer-Encoding headers within HTTP requests, creating a potential for protocol confusion that can be exploited across proxy configurations. The vulnerability manifests when an HTTP/1.1 persistent connection encounters both headers, leading to ambiguous parsing behavior that can result in incorrect interpretation of request entities. According to CWE-1004, this represents a security weakness where the application does not properly handle ambiguous or conflicting HTTP headers, creating potential attack vectors through protocol interpretation inconsistencies.
The technical implementation of this vulnerability exploits the inconsistent handling of HTTP headers by aiohttp's parser, which processes Transfer-Encoding values differently than other HTTP entities in the chain. When a request contains both Content-Length and Transfer-Encoding headers, the frontend reverse proxy may ignore the Transfer-Encoding header while processing Content-Length, creating a mismatch that allows attackers to manipulate request parsing. The specific exploitation technique involves using a Transfer-Encoding value like "chunked123" that aiohttp accepts but would be ignored by the frontend proxy, allowing an attacker to bypass proxy security controls. This behavior aligns with ATT&CK technique T1566.001 for initial access through spearphishing attachments, where protocol manipulation can be used to bypass security controls.
The operational impact of this vulnerability extends beyond simple protocol confusion, enabling attackers to poison sockets and affect other users within the same connection pool. This cross-user contamination can result in authentication header leakage, where sensitive credentials intended for one user may be inadvertently shared with others. The vulnerability becomes particularly dangerous when combined with other attack vectors such as open redirects, allowing attackers to redirect users to malicious sites while logging their requests. The exploitation scenario demonstrates how an attacker could manipulate proxy configurations to bypass security rules and potentially gain unauthorized access to systems or data. This represents a critical security flaw in HTTP protocol handling that can compromise the integrity of connection management and user isolation within web applications.
The remediation for CVE-2023-47641 was implemented in aiohttp version 3.8.0, which addresses the inconsistent header interpretation by enforcing stricter validation of HTTP protocol headers. Organizations using affected versions of aiohttp should immediately upgrade to the patched release to mitigate the risk of protocol confusion attacks. The vulnerability does not have any known workarounds since the issue stems from fundamental parsing behavior that cannot be easily circumvented without modifying the core HTTP processing logic. Security practitioners should monitor their deployments for instances of vulnerable aiohttp versions and ensure all reverse proxy configurations properly validate and normalize HTTP headers to prevent exploitation of this class of vulnerability. The fix demonstrates the importance of proper HTTP protocol implementation and the need for consistent header handling across all components in HTTP request processing chains.