CVE-2026-69243 in aiohttp
Summary
by MITRE • 08/04/2026
AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to 3.14.2, the HTTP parsers were vulnerable to a request smuggling attack relating to WebSocket upgrades. If using the server-side component, an attacker may be able to execute a request smuggling vulnerability using an edge case in the WebSocket upgrade procedure. A WebSocket upgrade request with a body could cause the parser to switch protocols before the complete request body was received, leaving trailing bytes to be handled as upgraded-protocol or pipelined data rather than normal HTTP body data. This issue is fixed in version 3.14.2.
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Analysis
by VulDB Data Team • 08/04/2026
The aiohttp asynchronous HTTP client/server framework for asyncio and Python contains a critical vulnerability in its HTTP parser implementation that enables request smuggling attacks through WebSocket upgrade procedures. This vulnerability affects versions prior to 3.14.2 and specifically targets the server-side component where the parsing logic fails to properly handle edge cases during WebSocket protocol upgrades. The flaw arises from an improper state transition within the HTTP parser when processing upgrade requests that contain request bodies, creating a window where the parser prematurely switches protocols before completing the reception of the entire request body.
The technical implementation of this vulnerability stems from how aiohttp handles the WebSocket upgrade process in its HTTP parsing layer. When a client sends a WebSocket upgrade request containing a request body, the parser enters an inconsistent state where it begins processing the upgrade protocol transition while still expecting to receive the complete HTTP request payload. This race condition between protocol switching and data reception causes trailing bytes from the original request body to be misinterpreted as either upgraded-protocol data or pipelined HTTP requests rather than standard HTTP body content. The parser's inability to correctly distinguish between these different data streams creates a fundamental breakdown in the HTTP protocol handling mechanism.
The operational impact of this vulnerability extends beyond simple parsing errors and presents significant security implications for applications using aiohttp server components. Attackers can exploit this weakness to manipulate how subsequent requests are processed, potentially enabling them to inject malicious content into following requests or bypass security controls that depend on proper HTTP request boundaries. The vulnerability allows for protocol confusion where the server may incorrectly process what should be separate HTTP requests as a single malformed request, creating opportunities for data leakage, authentication bypasses, or other malicious activities that leverage the improper handling of request boundaries.
This vulnerability aligns with several cybersecurity frameworks and threat models, particularly mapping to CWE-1296 which addresses improper handling of protocol transitions in web applications. The attack vector follows patterns consistent with HTTP request smuggling techniques documented in various security advisories, where attackers manipulate parser state to achieve unintended protocol behavior. From an ATT&CK framework perspective, this vulnerability could enable techniques such as T1071.004 for application layer protocol manipulation and potentially lead to privilege escalation through server-side request forgery or command injection if the misinterpreted data reaches processing components that execute arbitrary code. The fix implemented in version 3.14.2 addresses this by ensuring proper state management during WebSocket upgrade procedures, requiring complete request body reception before protocol switching occurs.
Organizations using aiohttp server components should immediately update to version 3.14.2 or later to mitigate this vulnerability, as the issue affects the core HTTP parsing functionality that underpins all web application security measures. Security teams should also conduct thorough assessments of applications that rely on WebSocket upgrade functionality, particularly those handling sensitive data or implementing authentication mechanisms that could be exploited through request smuggling attacks. Network monitoring should be enhanced to detect unusual patterns in HTTP request processing that might indicate exploitation attempts, while also ensuring proper input validation and sanitization at all application layers to prevent potential secondary impacts if attackers do manage to exploit this vulnerability through other means.