---
id: CVE-2026-34517
aliases:
  - GHSA-3wq7-rqq7-wx6j
  - PYSEC-2026-2099
title: >-
  AIOHTTP has late size enforcement for non-file multipart fields causes memory
  DoS
summary: >-
  AIOHTTP has late size enforcement for non-file multipart fields causes memory
  DoS
severity: low
vendor: aiohttp
product: aiohttp
ecosystem: pip
affected:
  - aiohttp < 3.13.4
patched:
  - aiohttp 3.13.4
published: '2026-04-01'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T03:50:42.683852324Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-3wq7-rqq7-wx6j'
references:
  - url: >-
      https://github.com/aio-libs/aiohttp/security/advisories/GHSA-3wq7-rqq7-wx6j
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-34517'
  - url: >-
      https://github.com/aio-libs/aiohttp/commit/cbb774f38330563422ca0c413a71021d7b944145
  - url: 'https://github.com/aio-libs/aiohttp'
  - url: 'https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4'
tags:
  - osv
  - pip
epss: 0.00507
epssPercentile: 0.4062
ingestedAt: '2026-07-13T18:57:52.125Z'
---

## Overview

### Summary

For some multipart form fields, aiohttp read the entire field into memory before checking client_max_size.

### Impact

If an application uses `Request.post()` an attacker can send a specially crafted multipart request to force significant temporary memory allocation even when the request is ultimately rejected.

-----

Patch: https://github.com/aio-libs/aiohttp/commit/cbb774f38330563422ca0c413a71021d7b944145

## Affected packages

- `aiohttp < 3.13.4`

## Remediation

Upgrade to a patched release:

- `aiohttp 3.13.4`