# CVE-2026-34519: AIOHTTP has HTTP response splitting via \r in reason phrase

Source: https://junglewise.ai/threats/cve-2026-34519-aiohttp-has-http-response-splitting-via-r-in-reason-phrase  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-01  
License: CC BY 4.0 with a link back

CVE-2026-34519 · Severity: medium · CVSS 5.3 · Published 2026-04-01

AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.13.4, an attacker who controls the reason parameter when creating a Response may be able to inject extra headers or similar exploits. 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-2026-34519 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-34519 being exploited in the wild.

**How severe is CVE-2026-34519?** Medium severity, with a CVSS score of 5.3, 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-2026-34519?** 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-2026-34519?** 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-2026-34519
- GHSA-mwh4-6h8g-pg8w
- PYSEC-2026-2101

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