---
id: "CVE-2021-30663"
kind: "vulnerability"
aliases: ["CVE-2021-30663"]
title: "Apple Multiple Products: Apple Multiple Products WebKit Integer Overflow Vulnerability"
severity: "high"
cvss: 8.8
epss: 0.03521
exploited: true
status: "open"
category: "vendor"
products: [{"name": "Apple Multiple Products", "fixed": [], "affected": "", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["apple", "exploited", "ios", "macos", "safari", "vendor", "webkit"]
not_affected_if: ["fully-patched-devices"]
published_at: "2021-09-08T15:15:13+00:00"
first_seen_at: "2026-10-23T19:11:53+00:00"
updated_at: "2026-10-23T21:57:35+00:00"
sources: [{"source": "kev", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-30663", "first_seen_at": "2026-10-23T19:11:53+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2021-30663", "first_seen_at": "2026-10-23T19:13:44+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-30663", "first_seen_at": "2026-10-23T21:57:35+00:00"}]
---

# Apple Multiple Products: Apple Multiple Products WebKit Integer Overflow Vulnerability

An integer overflow in Apple's WebKit browser engine lets a crafted web page run code when it is processed, affecting iOS, iPadOS, macOS, tvOS and Safari. The CISA KEV catalog lists it as actively exploited in the wild.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:Apple Multiple Products affected ? fixed ?

## How to check

Check the device OS version (iOS/iPadOS Settings > General > About, macOS About This Mac) against Apple's security notes for this CVE.

## Fix

Update iOS, iPadOS, macOS, tvOS and Safari to a release that includes Apple's fix for CVE-2021-30663, as CISA directs (apply updates per vendor instructions).

## Timeline

- 2026-10-23T19:11:53+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-30663
- 2026-10-23T19:13:44+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2021-30663
- 2026-10-23T21:57:35+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2021-30663

## From the sources

Apple iOS, iPadOS, macOS, tvOS, and Safari WebKit contain an integer overflow vulnerability that leads to code execution when processing maliciously crafted web content. This vulnerability could impact HTML parsers that use WebKit, including but not limited to Apple Safari and non-Apple products which rely on WebKit for HTML processing.

CISA required action: Apply updates per vendor instructions.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_