What is CVE-2026-34518?

CVE-2026-34518 is a medium-severity vulnerability in Aiohttp, classified under Information Disclosure. CVSS score: 5.3/10. Published 2026-04-01.

How severe is CVE-2026-34518?

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

Information disclosure in Aiohttp

CVE-2026-34518

AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.13.4, when following redirects to a different origin, aiohttp drops the Authorization header, but retains the Cookie and Proxy-Authorization headers. This issue has been patched in version 3.13.4.

Vulnerability class: Information Disclosure

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:L/I:N/A:N.

EPSS exploit prediction

EPSS: 0.004 (32.2th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 32nd percentile — 32.2% 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-200 — Information Disclosure

References

github.com/aio-libs/aiohttp/security/advisories/GHSA-966j-vmvw-g2g9 (Patch, Vendor Advisory)
github.com/aio-libs/aiohttp/commit/5351c980dcec7ad385730efdf4e1f4338b24fdb6 (Patch)
github.com/aio-libs/aiohttp/releases/tag/v3.13.4 (Release Notes)

Frequently asked questions

What is CVE-2026-34518?: CVE-2026-34518 is a medium-severity vulnerability in Aiohttp, classified under Information Disclosure. CVSS score: 5.3/10. Published 2026-04-01.
How severe is CVE-2026-34518?: Medium severity. CVSS v3 base score is 5.3 out of 10.