What is CVE-2026-34519?

CVE-2026-34519 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-2026-34519?

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

Vulnerability in Aiohttp

CVE-2026-34519

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 i…

EPSS: 0.003 (21.3th percentile) — read the EPSS interpretation.

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.

Affected products

Aiohttp
Aio-libs Aiohttp — versions < 3.13.4

Weakness classification (CWE)

CWE-113 — HTTP Response Splitting

References

security-advisories@github.com (x_refsource_CONFIRM, Patch, Vendor Advisory)
security-advisories@github.com (Patch, x_refsource_MISC)
security-advisories@github.com (x_refsource_MISC, Release Notes)

Frequently asked questions

What is CVE-2026-34519?: CVE-2026-34519 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-2026-34519?: Medium severity. CVSS v3 base score is 5.3 out of 10.