# CVE-2026-34516: AIOHTTP has a Multipart Header Size Bypass

Source: https://junglewise.ai/threats/cve-2026-34516-aiohttp-has-a-multipart-header-size-bypass  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-01  
License: CC BY 4.0 with a link back

CVE-2026-34516 · Severity: high · CVSS 7.5 · Published 2026-04-01

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.

Technologies: [Aiohttp](https://junglewise.ai/threats/technologies/aiohttp-aiohttp), [aiohttp (PyPI)](https://junglewise.ai/threats/technologies/aiohttp). Vendors: [Aiohttp](https://junglewise.ai/threats/vendors/aiohttp), [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-34516 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-34516 being exploited in the wild.

**How severe is CVE-2026-34516?** High severity, with a CVSS score of 7.5, published 1 April 2026.

**Which products and versions are affected?** aiohttp (PyPI) ECOSYSTEM:introduced=0,fixed=3.13.4.

**Is there a fix for CVE-2026-34516?** Yes. aiohttp (PyPI): upgrade to 3.13.4 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2026-34516?** Check whether you run Aiohttp or aiohttp (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- aiohttp (PyPI): upgrade to 3.13.4 or later

  ```sh
  pip install "aiohttp>=3.13.4"
  ```


## Affected products

- Aiohttp
- aiohttp (PyPI) ECOSYSTEM:introduced=0,fixed=3.13.4

## Identifiers

- CVE-2026-34516
- GHSA-m5qp-6w8w-w647
- PYSEC-2026-2098

## Related threats

- [aiohttp HTTP request smuggling in pure Python parser](https://junglewise.ai/threats/cve-2026-111750-aiohttp-is-an-asynchronous-http-client-server-framework-for)
- [aiohttp host-only cookie scope bypass in subdomain handling](https://junglewise.ai/threats/cve-2026-111749-aiohttp-is-an-asynchronous-http-client-server-framework-for)
- [aiohttp Request scheme manipulation in absolute-form requests](https://junglewise.ai/threats/cve-2026-111748-aiohttp-is-an-asynchronous-http-client-server-framework-for)
- [AIOHTTP multipart request file descriptor exhaustion](https://junglewise.ai/threats/cve-2026-111066-aiohttp-is-an-asynchronous-http-client-server-framework-for)
- [aiohttp cookie Max-Age integer overflow causes connection pool exhaustion](https://junglewise.ai/threats/cve-2026-111065-aiohttp-is-an-asynchronous-http-client-server-framework-for)