What is CVE-2026-9939?

CVE-2026-9939 is a high-severity vulnerability in Apple macOS, classified under Heap-based Buffer Overflow. CVSS score: 8.8/10. Published 2026-05-28.

How severe is CVE-2026-9939?

High severity. CVSS v3 base score is 8.8 out of 10.

Buffer overflow in Apple macOS

CVE-2026-9939

Heap buffer overflow in WebCodecs in Google Chrome prior to 148.0.7778.216 allowed a remote attacker to execute arbitrary code inside a sandbox via a crafted HTML page. (Chromium security severity: High)

Vulnerability class: Buffer Overflow

Published 2026-05-28 · last modified 2026-07-21.

CVSS v3 metric

CVSS v3 base score 8.8 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.006 (45.4th percentile), scored 2026-10-02.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 45th percentile — 45.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.004 · newest: 0.006 · change: +0.002

Affected products

Weakness classification (CWE)

CWE-122 — Heap-based Buffer Overflow

References

chromereleases.googleblog.com/2026/05/stable-channel-update-for-desktop_0877304… (Release Notes, Vendor Advisory)
issues.chromium.org/issues/502735235 (Permissions Required)

Frequently asked questions

What is CVE-2026-9939?: CVE-2026-9939 is a high-severity vulnerability in Apple macOS, classified under Heap-based Buffer Overflow. CVSS score: 8.8/10. Published 2026-05-28.
How severe is CVE-2026-9939?: High severity. CVSS v3 base score is 8.8 out of 10.