How severe is CVE-2021-30663?

CVE-2021-30663 has a CVSS 3.1 base score of 7.8 (HIGH). EPSS estimates a 3.5% probability of exploitation in the next 30 days. It is listed in the CISA Known Exploited Vulnerabilities catalog.

CVE-2021-30663: Apple Multiple Products WebKit Integer Overflow

CISA Known Exploited Vulnerabilities

Apple Multiple Products WebKit Integer Overflow Vulnerability is confirmed as actively exploited and is listed in the CISA KEV catalog.

Added to KEV

2021-11-03

Remediation due

2021-11-17

Required action
Apply updates per vendor instructions.

CISA notes
https://nvd.nist.gov/vuln/detail/CVE-2021-30663

Description

An integer overflow was addressed with improved input validation. This issue is fixed in iOS 14.5.1 and iPadOS 14.5.1, tvOS 14.6, iOS 12.5.3, Safari 14.1.1, macOS Big Sur 11.3.1. Processing maliciously crafted web content may lead to arbitrary code execution.

Severity

CVSS 3.1 · CISA7.8 HIGH

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

SSVC · CISA-ADP

Exploitationactive

Automatableno

Technical impacttotal

Exploitation Context

as of October 14, 2026

All KEV statistics→

CISA added CVE-2021-30663 to the KEV catalog 56 days after its CVE record was published.
It is one of 95 Apple entries in the CISA KEV catalog, and one of 23 added in 2021.
Its current EPSS score (3.5%) is higher than that of 14% of CISA KEV entries.

Affected Products

Vendor	Product	Affected versions
Apple	Apple macOS	unspecified to <11.3
Apple	Apple macOS	unspecified to <14.5
Apple	Apple macOS	unspecified to <12.5
Apple	Apple macOS	unspecified to <14.6
Apple	Apple macOS	unspecified to <14.1

References

5 Links

Other references

Record Details

Published

2021-09-08

Last updated

2025-10-21

Assigner (CNA)

apple

Credited to

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CVE record data © The MITRE Corporation, used under the CVE Terms of Use. Exploited-in-the-wild data from the CISA Known Exploited Vulnerabilities catalog (CC0). Exploit prediction scores by FIRST EPSS (first.org/epss). This site is not endorsed or certified by MITRE, NVD, CISA, or FIRST.