CVE-2026-111064 in aiohttp
Summary
by MITRE • 10/19/2026
AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to 3.14.4, keepalive timeout handling is absent during the initial portion of a request. An attacker can keep an idle connection open indefinitely before sending any request data, consuming server connection capacity. This issue is fixed in version 3.14.4.
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Analysis
by VulDB Data Team • 10/19/2026
The vulnerability identified within AIOHTTP versions prior to 3.14.4 represents a significant flaw in the handling of keepalive connections during the initial phase of an HTTP request lifecycle. Asynchronous frameworks like AIOHTTP are designed to handle high volumes of concurrent network operations efficiently by maintaining persistent connections, which reduces the overhead associated with establishing new TCP sessions for each subsequent interaction. However, this efficiency mechanism introduces a specific attack surface when timeout logic is not uniformly applied across all stages of connection management. In the affected versions, the server fails to enforce keepalive timeouts during the period between the initial acceptance of a TCP connection and the receipt of any actual HTTP request data from the client. This gap allows an adversary to establish a valid TCP handshake with the AIOHTTP-based service and then remain idle indefinitely without transmitting any payload or headers that would trigger standard request-level timeout mechanisms.
This behavior directly facilitates resource exhaustion attacks, specifically targeting the server's connection pool capacity. Since each open keepalive connection consumes system resources such as file descriptors, memory buffers, and thread or event loop slots, an attacker can leverage this flaw to multiply their impact by opening a large number of idle connections simultaneously. By keeping these sockets in a half-open or established-but-idle state for extended periods, the attacker effectively starves legitimate users of available connection endpoints. This denial-of-service condition does not require sending malicious payloads or exploiting complex logic errors; it relies solely on the passive consumption of resources through prolonged connectivity. The impact is particularly severe in environments where AIOHTTP handles a high degree of concurrency, as even a moderate number of idle connections can degrade performance significantly or cause complete service unavailability depending on the configured limits and available system memory.
From a classification perspective, this vulnerability aligns with CWE-400, which describes Uncontrolled Resource Consumption, specifically manifesting as resource exhaustion through connection flooding. It also maps to MITRE ATT&CK technique T1499, Endpoint Denial of Service, where the attacker's goal is to degrade or disrupt services by consuming critical resources such as network connections. The absence of a timeout mechanism during the pre-request phase indicates an incomplete implementation of state management for idle clients, which contradicts best practices for robust HTTP server design that mandate strict limits on connection lifetime regardless of data transmission activity.
The resolution provided in AIOHTTP version 3.14.4 addresses this gap by implementing appropriate keepalive timeout handling during the initial portion of a request. This ensures that connections are not held open indefinitely if no data is received within a defined timeframe, thereby preventing attackers from monopolizing server resources through idle persistence. To mitigate similar risks in other systems or while upgrading to the patched version, administrators should ensure that their reverse proxies and load balancers enforce strict connection timeouts for upstream services. Additionally, configuring application-level keepalive settings with reasonable durations can provide an additional layer of defense against resource exhaustion attacks. Regular monitoring of active connections and alerting on anomalous spikes in idle connection counts can also aid in the early detection of such exploitation attempts before they lead to service disruption.