---
id: "CVE-2021-1870"
kind: "vulnerability"
aliases: ["CVE-2021-1870"]
title: "Apple iOS, iPadOS, and macOS: Apple iOS, iPadOS, and macOS WebKit Remote Code Execution Vulnerability"
severity: "critical"
cvss: 9.8
epss: 0.0771
exploited: true
status: "open"
category: "vendor"
products: [{"name": "Apple iOS, iPadOS, and macOS", "fixed": [], "affected": "", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["exploited", "ios", "ipados", "macos", "safari", "vendor", "webkit"]
not_affected_if: ["unpatched-devices-not-in-use"]
published_at: "2021-04-02T19:15:20+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-2021-1870", "first_seen_at": "2026-10-23T19:11:53+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2021-1870", "first_seen_at": "2026-10-23T19:13:44+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-1870", "first_seen_at": "2026-10-23T21:57:35+00:00"}]
---

# Apple iOS, iPadOS, and macOS: Apple iOS, iPadOS, and macOS WebKit Remote Code Execution Vulnerability

A logic flaw in WebKit, the browser engine used by Safari and iOS, iPadOS and macOS, lets a remote attacker execute code. Any app that parses HTML with WebKit is also exposed, and CISA lists it as actively exploited.

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

## Affected

- vendor:Apple iOS, iPadOS, and macOS affected ? fixed ?

## Fix

Update iOS, iPadOS and macOS to a release that includes Apple's fix; the sources do not name the exact version.
Update any non-Apple app that embeds WebKit for HTML processing.

## Timeline

- 2026-10-23T19:11:53+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-1870
- 2026-10-23T19:13:44+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2021-1870
- 2026-10-23T21:57:35+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2021-1870

## From the sources

Apple iOS, iPadOS, and macOS WebKit contain an unspecified logic vulnerability that allows a remote attacker to execute code. 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_