CVE-2026-34520 — CRITICAL (9.1)

Q: How severe is CVE-2026-34520?

CVE-2026-34520 has been rated CRITICAL with a CVSS base score of 9.1/10. This is considered a critical vulnerability requiring immediate attention.

Q: Is there a patch for CVE-2026-34520?

Check the references section above for vendor advisories and patch information. Affected products include: Aiohttp Aiohttp.

Vulnerability Description

AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.13.4, the C parser (the default for most installs) accepted null bytes and control characters in response headers. This issue has been patched in version 3.13.4.

CVSS Score

9.1

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

NONE

Scope

UNCHANGED

Confidentiality

NONE

Integrity

HIGH

Availability

HIGH

Affected Products

Vendor	Product	Versions
Aiohttp	Aiohttp	< 3.13.4

Related Weaknesses (CWE)

CWE-113

References

https://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109Patch
https://github.com/aio-libs/aiohttp/releases/tag/v3.13.4Release Notes
https://github.com/aio-libs/aiohttp/security/advisories/GHSA-63hf-3vf5-4wqfPatchVendor Advisory

FAQ

What is CVE-2026-34520?

CVE-2026-34520 is a vulnerability with a CVSS score of 9.1 (CRITICAL). AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.13.4, the C parser (the default for most installs) accepted null bytes and control characters in resp...

How severe is CVE-2026-34520?

CVE-2026-34520 has been rated CRITICAL with a CVSS base score of 9.1/10. This is considered a critical vulnerability requiring immediate attention.

Is there a patch for CVE-2026-34520?

Check the references section above for vendor advisories and patch information. Affected products include: Aiohttp Aiohttp.