What is CVE-2026-34514?

CVE-2026-34514 is a medium-severity vulnerability in Aiohttp, classified under HTTP Response Splitting. CVSS score: 5.3/10. Published 2026-04-01.

How severe is CVE-2026-34514?

Medium severity. CVSS v3 base score is 5.3 out of 10.

Vulnerability in Aiohttp

CVE-2026-34514

AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.13.4, an attacker who controls the content_type parameter in aiohttp could use this to inject extra headers or similar exploits. This issue has been patched in version 3.13.4.

Published 2026-04-01 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N.

EPSS exploit prediction

EPSS: 0.004 (31.4th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 31st percentile — 31.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.003 · newest: 0.004 · change: +0.001

Affected products

Aiohttp
Aio-Libs Aiohttp — versions < 3.13.4

Weakness classification (CWE)

CWE-113 — HTTP Response Splitting

References

github.com/aio-libs/aiohttp/security/advisories/GHSA-2vrm-gr82-f7m5 (Patch, Vendor Advisory)
github.com/aio-libs/aiohttp/commit/9a6ada97e2c6cf1ce31727c6c9fcea17c21f6f06 (Patch)
github.com/aio-libs/aiohttp/releases/tag/v3.13.4 (Release Notes)

Frequently asked questions

What is CVE-2026-34514?: CVE-2026-34514 is a medium-severity vulnerability in Aiohttp, classified under HTTP Response Splitting. CVSS score: 5.3/10. Published 2026-04-01.
How severe is CVE-2026-34514?: Medium severity. CVSS v3 base score is 5.3 out of 10.