How severe is CVE-2021-30666?

CVE-2021-30666 has a CVSS 3.1 base score of 8.8 (HIGH). EPSS estimates a 3.0% probability of exploitation in the next 30 days. It is listed in the CISA Known Exploited Vulnerabilities catalog.

CVE-2021-30666: Apple iOS WebKit Buffer Overflow Vulnerability

CISA Known Exploited Vulnerabilities

Apple iOS WebKit Buffer 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-2021-30666

Description

A buffer overflow issue was addressed with improved memory handling. This issue is fixed in iOS 12.5.3. Processing maliciously crafted web content may lead to arbitrary code execution. Apple is aware of a report that this issue may have been actively exploited..

Severity

CVSS 3.1 · CISA8.8 HIGH

CVSS:3.1/AV:N/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 17, 2026

All KEV statistics→

CISA added CVE-2021-30666 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 (3.0%) is higher than that of 12% of CISA KEV entries.

Affected Products

Vendor	Product	Affected versions
Apple	Apple iOS	unspecified to <12.5

References

1 Links

Other references

https://support.apple.com/en-us/HT212341

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.