How severe is CVE-2020-9866?

CVE-2020-9866 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2020-9866 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (77th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2020-9866?

CVE-2020-9866 affects Apple Mac Os X. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2020-9866?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2020-9866 published?

CVE-2020-9866 was published on 2020-10-27 and last updated on 2026-06-17.

CVE-2020-9866

CVE-2020-9866 is a critical-severity vulnerability in Apple Mac Os X with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-120.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 2% (77th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-120
Affected product: Apple Mac Os X
Published: 2020-10-27
Last modified: 2026-06-17

Description

A buffer overflow was addressed with improved bounds checking. This issue is fixed in macOS Catalina 10.15.6, Security Update 2020-004 Mojave, Security Update 2020-004 High Sierra. A buffer overflow may result in arbitrary code execution.

Frequently asked questions

What is CVE-2020-9866?: A buffer overflow was addressed with improved bounds checking. This issue is fixed in macOS Catalina 10.15.6, Security Update 2020-004 Mojave, Security Update 2020-004 High Sierra. A buffer overflow may result in arbitrary code execution.
How severe is CVE-2020-9866?: CVE-2020-9866 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2020-9866 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (77th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2020-9866?: CVE-2020-9866 affects Apple Mac Os X. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2020-9866?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2020-9866 published?: CVE-2020-9866 was published on 2020-10-27 and last updated on 2026-06-17.

References

https://support.apple.com/en-us/HT211289

Affected products (1)

cpe:2.3:o:apple:mac_os_x:*:*:*:*:*:*:*:*

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