CVE-2025-69229 is a resource exhaustion vulnerability categorized under CWE-770 (Allocation of Resources Without Limits or Throttling) affecting aiohttp, a widely used asynchronous HTTP client/server framework for Python's asyncio. Versions 3.13.2 and below improperly handle chunked HTTP messages, specifically when the request.read() method is invoked on endpoints receiving chunked data. The vulnerability manifests as excessive blocking CPU usage during the processing of a large number of chunks, with each malicious request potentially causing the server to spend approximately one second of CPU time in a blocking state. This behavior can be exploited by an unauthenticated remote attacker to launch a denial-of-service (DoS) attack by overwhelming the server with numerous such requests, thereby degrading its ability to serve legitimate traffic. The vulnerability does not require user interaction and can be triggered remotely over the network. The CVSS v4.0 score is 6.6 (medium severity), reflecting the network attack vector, low attack complexity, no privileges or user interaction required, and a high impact on availability. The vulnerability was publicly disclosed on January 5, 2026, and is fixed in aiohttp version 3.13.3. No known exploits have been reported in the wild to date. Given aiohttp's popularity in Python-based asynchronous web applications and microservices, this vulnerability poses a tangible risk to applications that process chunked HTTP requests without additional throttling or resource management controls.

For European organizations, the primary impact is the risk of denial-of-service conditions on web services or APIs built using vulnerable aiohttp versions. This can lead to service unavailability, degraded user experience, and potential operational disruptions, especially for organizations relying on Python-based asynchronous frameworks for critical applications. Industries such as finance, e-commerce, healthcare, and public services that deploy aiohttp in their backend infrastructure could face interruptions affecting customers and internal users. Additionally, the increased CPU usage could lead to higher infrastructure costs or trigger automated scaling mechanisms unnecessarily. While the vulnerability does not directly compromise confidentiality or integrity, the availability impact alone can have significant business consequences. Organizations with high traffic volumes or exposed APIs are particularly at risk. The lack of authentication requirements means attackers can exploit this remotely without credentials, increasing the threat surface. Given the moderate CPU blocking time per request, large-scale attacks could amplify the impact substantially.

European organizations should immediately upgrade all aiohttp dependencies to version 3.13.3 or later to eliminate the vulnerability. In addition to patching, organizations should implement rate limiting and request throttling on endpoints that process chunked HTTP requests to prevent resource exhaustion. Deploying Web Application Firewalls (WAFs) with rules to detect and block abnormal chunked request patterns can provide an additional layer of defense. Monitoring CPU usage and request patterns for anomalies can help detect exploitation attempts early. For critical services, consider isolating aiohttp-based components behind reverse proxies that can enforce stricter traffic controls. Developers should review application code to avoid unnecessary use of request.read() on untrusted inputs or implement application-level limits on chunk sizes and counts. Finally, ensure that incident response plans include procedures for mitigating DoS attacks targeting asynchronous Python services.