Inefficient Algorithmic Complexity in aiohttp - #VU162576
Published: November 9, 2026
Vulnerability identifier: #VU162576
CSH Severity: Medium
CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N]
CVE-ID: N/A
CWE-ID: CWE-407
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows an unauthenticated remote attacker to block an aiohttp server's event loop and disrupt request processing.
The vulnerability exists due to a missing field-count limit in URL-encoded form parsing by Request.post(), causing quadratic processing time for repeated keys. An unauthenticated remote attacker can submit a form POST within the default client_max_size to a handler that calls Request.post() and stall the event loop.
Affected software
aiohttp
Remediation
Install security update from vendor's website.
aiohttp - update to 3.14.4