---
id: "CVE-2021-1879"
kind: "vulnerability"
aliases: ["CVE-2021-1879"]
title: "Apple iOS, iPadOS, and watchOS: Apple iOS, iPadOS, and watchOS WebKit Cross-Site Scripting (XSS) Vulnerability"
severity: "high"
cvss: 6.1
epss: 0.07082
exploited: true
status: "open"
category: "vendor"
products: [{"name": "Apple iOS, iPadOS, and watchOS", "fixed": [], "affected": "", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["exploited", "ios", "ipados", "safari", "vendor", "watchos", "webkit"]
not_affected_if: ["unpatched-os-versions-only"]
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-2021-1879", "first_seen_at": "2026-10-23T19:11:53+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2021-1879", "first_seen_at": "2026-10-23T19:13:44+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-1879", "first_seen_at": "2026-10-23T21:57:35+00:00"}]
---

# Apple iOS, iPadOS, and watchOS: Apple iOS, iPadOS, and watchOS WebKit Cross-Site Scripting (XSS) Vulnerability

A WebKit flaw in Apple iOS, iPadOS and watchOS lets crafted web content run script in pages it should not reach. Attackers can use it to read data and act as the user in other sites, 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 watchOS affected ? fixed ?

## How to check

Settings > General > About on each iPhone, iPad or Apple Watch and compare the version with Apple's patched release notes

## Fix

Update iOS, iPadOS and watchOS to a release that includes the fix, per Apple's security release notes for CVE-2021-1879
Apps that embed WebKit (non-Safari browsers and in-app web views) also need their own updates

## Timeline

- 2026-10-23T19:11:53+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-1879
- 2026-10-23T19:13:44+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2021-1879
- 2026-10-23T21:57:35+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2021-1879

## From the sources

Apple iOS, iPadOS, and watchOS WebKit contain an unspecified vulnerability that allows for universal cross-site scripting (XSS) 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.

---

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