What is CVE-2026-70309?

CVE-2026-70309 is a medium-severity vulnerability in Microsoft Edge Chromium, classified under Origin Validation Error. CVSS score: 5.4/10. Published 2026-08-28.

How severe is CVE-2026-70309?

Medium severity. CVSS v3 base score is 5.4 out of 10.

Vulnerability in Microsoft Edge Chromium

CVE-2026-70309

Origin validation error in Microsoft Edge (Chromium-based) allows an unauthorized attacker to bypass a security feature over a network.

Published 2026-08-28 · last modified 2026-08-31.

CVSS v3 metric

CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.002 (10.6th percentile), scored 2026-10-13.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 11th percentile — 10.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: +0.001

Affected products

Weakness classification (CWE)

CWE-346 — Origin Validation Error

References

Microsoft Edge (Chromium-based) Security Feature Bypass Vulnerability (vendor-advisory, patch, Vendor Advisory)

Frequently asked questions

What is CVE-2026-70309?: CVE-2026-70309 is a medium-severity vulnerability in Microsoft Edge Chromium, classified under Origin Validation Error. CVSS score: 5.4/10. Published 2026-08-28.
How severe is CVE-2026-70309?: Medium severity. CVSS v3 base score is 5.4 out of 10.