What is CVE-2021-30805?

CVE-2021-30805 is a critical-severity vulnerability in Apple macOS, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2021-09-08.

How severe is CVE-2021-30805?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Buffer overflow in Apple macOS

CVE-2021-30805

A memory corruption issue was addressed with improved input validation. This issue is fixed in macOS Big Sur 11.5, Security Update 2021-004 Catalina, Security Update 2021-005 Mojave. An application may be able to execute arbitrary code with kernel privileges.

Vulnerability class: Buffer Overflow

Published 2021-09-08 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.031 (87.5th percentile), scored 2026-10-02.

Low probability of exploitation in the next 30 days, but still tracked. 87th percentile — 87.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.031 · newest: 0.031 · change: 0.000

Affected products

Apple macOS — versions unspecified
Apple Mac OS X — versions 10.14.6, 10.15.6, 10.15.7
Apple Security Update - Catalina — versions unspecified

Weakness classification (CWE)

CWE-787 — Out-of-bounds Write

References

support.apple.com/en-us/HT212602 (Vendor Advisory)
support.apple.com/en-us/HT212600 (Vendor Advisory)
support.apple.com/en-us/HT212603 (Vendor Advisory)

Frequently asked questions

What is CVE-2021-30805?: CVE-2021-30805 is a critical-severity vulnerability in Apple macOS, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2021-09-08.
How severe is CVE-2021-30805?: Critical severity. CVSS v3 base score is 9.8 out of 10.