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Vulnerability · Published Apr 1, 2026 · Assigned by GitHub_M

CVE-2026-34516AIOHTTP: Multipart Header Size Bypass

High 7.5

In plain English

A high-severity resource allocation without limits in aiohttp from aio-libs. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 40% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High
Exploit odds (30 days)0.5%top 60.2% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.13.4, a response with an excessive number of multipart headers may be allowed to use more memory than intended, potentially allowing a DoS vulnerability. This issue has been patched in version 3.13.4.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Alpine:v3.23py3-aiohttp3.13.5-r0ALPINE-CVE-2026-34516
Alpine:v3.24py3-aiohttp3.13.5-r0ALPINE-CVE-2026-34516
Debian:12python-aiohttp3.8.4-1+deb12u2DEBIAN-CVE-2026-34516
Debian:13python-aiohttpno fix listedDEBIAN-CVE-2026-34516
Debian:14python-aiohttp3.13.5-1DEBIAN-CVE-2026-34516
PyPIaiohttp3.13.4GHSA-m5qp-6w8w-w647
PyPIaiohttp3.13.4PYSEC-2026-2098
Ubuntu:25.10python-aiohttpno fix listedUBUNTU-CVE-2026-34516
Ubuntu:26.10python-aiohttpno fix listedUBUNTU-CVE-2026-34516

Affected products (as reported)

VendorProductVersions
aio-libs aiohttp < 3.13.4

Weakness: CWE-770 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References