Bug 2573473 (CVE-2026-128126)

Summary: CVE-2026-128126 aiohttp: aiohttp: Denial of Service via excessive URL-encoded form fields
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: high    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in aiohttp. A remote attacker can cause a Denial of Service (DoS) by sending an HTTP POST request containing an excessive number of repeated fields in a URL-encoded form body. Because the framework does not limit the number of parsed form fields and processes duplicate keys inefficiently, handling such requests consumes excessive processing time and blocks the asynchronous event loop. This condition prevents the server from processing other incoming requests.
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Description OSIDB Bzimport 2026-11-13 20:41:34 UTC 
AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to 3.14.4, Request.post() does not limit the number of fields in a URL-encoded form body, and inserting many repeated keys into MultiDict takes quadratic time on the event loop. A remote attacker can send a form POST within client_max_size to a handler that calls Request.post() and block the event loop. This issue is fixed in version 3.14.4.