How severe is CVE-2021-43243?

Medium severity. CVSS v3 base score is 5.5 out of 10.

Vulnerability in Microsoft Vp9 Video Extensions

CVE-2021-43243

VP9 Video Extensions Information Disclosure Vulnerability

Published 2021-12-15 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.5 (Medium). Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N.

EPSS exploit prediction

EPSS: 0.008 (54.0th percentile), scored 2026-10-02.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 54th percentile — 54.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.008 · newest: 0.008 · change: 0.000

Affected products

References

portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-43243 (Patch, Vendor Advisory)

Frequently asked questions

What is CVE-2021-43243?: CVE-2021-43243 is a medium-severity vulnerability in Microsoft Vp9 Video Extensions. CVSS score: 5.5/10. Published 2021-12-15.
How severe is CVE-2021-43243?: Medium severity. CVSS v3 base score is 5.5 out of 10.