What is CVE-2020-9921?

CVE-2020-9921 is a high-severity vulnerability in Apple macOS, classified under Time-of-check Time-of-use (TOCTOU) Race Condition. CVSS score: 7.0/10. Published 2020-10-22.

How severe is CVE-2020-9921?

High severity. CVSS v3 base score is 7.0 out of 10.

Buffer overflow in Apple macOS

CVE-2020-9921

A memory corruption issue was addressed with improved memory handling. This issue is fixed in macOS Catalina 10.15.6. A malicious application may be able to execute arbitrary code with system privileges.

Vulnerability class: TOCTOU (Time-of-Check to Time-of-Use)

Published 2020-10-22 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.0 (High). Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.002 (12.0th percentile), scored 2026-10-01.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 12th percentile — 12.0% 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: 0.000

Affected products

Apple macOS — versions unspecified
Apple Mac OS X

Weakness classification (CWE)

References

support.apple.com/kb/HT211289 (Vendor Advisory)

Frequently asked questions

What is CVE-2020-9921?: CVE-2020-9921 is a high-severity vulnerability in Apple macOS, classified under Time-of-check Time-of-use (TOCTOU) Race Condition. CVSS score: 7.0/10. Published 2020-10-22.
How severe is CVE-2020-9921?: High severity. CVSS v3 base score is 7.0 out of 10.