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

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, aiohttp (PyPI). Vendors: Aiohttp, 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
    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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