CVE-2026-34517

AIOHTTP: Late size enforcement for non-file multipart fields causes memory DoS

Low2.7EPSS 0.40%

Published: 1 Apr 2026
Updated: 23 Jun 2026
Reserved: 30 Mar 2026
Assigned by: GitHub_M

Description

AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.13.4, for some multipart form fields, aiohttp read the entire field into memory before checking client_max_size. This issue has been patched in version 3.13.4.

Scores

CVSS scores of CVE-2026-34517, by who scored it
Scored by	CVSS	Score	Vector
GitHub_MCNA (assigner)	4.0	Low2.7	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/E:U
NVDNVD · Analyzed	4.0	Low2.7	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/E:U/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

EPSS (exploitation in 30 days): 0.40% · top 66% of all CVEs (6 Nov 2026)
CISA SSVC: Exploitation: none · Automatable: yes · Technical impact: partial

The list uses the assigner's score when there is one, then CISA's, then NVD's: Low 2.7.

Weakness

CWE-770: Allocation of Resources Without Limits or Throttling (opens in a new tab)All about CWE-770 and its CVEs

Affected products

aio-libs · aiohttp
- affected < 3.13.4

Affected packages

From reviewed advisories of the GitHub Advisory Database.

PyPIaiohttpGHSA-3wq7-rqq7-wx6j (opens in a new tab)

References (3)

https://github.com/aio-libs/aiohttp/security/advisories/GHSA-3wq7-rqq7-wx6j (opens in a new tab)x_refsource_CONFIRM
https://github.com/aio-libs/aiohttp/commit/cbb774f38330563422ca0c413a71021d7b944145 (opens in a new tab)x_refsource_MISC
https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4 (opens in a new tab)x_refsource_MISC

Sources

The same CVE in the primary databases and aggregators, to check against.

Badge for a README or a ticket

[![CVE-2026-34517](https://trackcve.app/badge/CVE-2026-34517.svg)](https://trackcve.app/cve/CVE-2026-34517)

Record last updated 23 Jun 2026, 15:50 UTC.