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

Severity: high (CVSS 8.8 v3.1)
Exploited in the wild: yes — in CISA KEV since 2021-11-03
EPSS: 3.0% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-09-08 · updated 2026-06-17
Weakness: CWE-119

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..

Affected products

Apple Iphone Os: before 12.5.3 — fixed in 12.5.3

How to fix

Upgrade to a fixed version: Apple Iphone Os 12.5.3. Check the vendor advisory for mitigations.

References

https://support.apple.com/en-us/HT212341
https://support.apple.com/en-us/HT212341
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-30666

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