CVE-2021-1879

CVE-2021-1879 is a universal cross-site scripting (UXSS) flaw in the WebKit browser engine affecting iOS, iPadOS, and watchOS, caused by an object-lifetime management error. An attacker can trigger it by convincing a user to process maliciously crafted web content (e.g., visiting an attacker-controlled page in Safari or another WebKit-based browser), allowing the attacker to bypass the same-origin policy and read or modify content of other sites in the browser. Successful exploitation is rated Medium severity (CVSS 6.1) because it requires user interaction, but it can leak sensitive data such as cookies, session tokens, or page content. Any user of an iPhone, iPad, or Apple Watch running software older than iOS 12.5.2, iOS 14.4.2/iPadOS 14.4.2, or watchOS 7.3.3 is affected. Apple reported that the issue may have been actively exploited in the wild at the time of patching, it is on the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), and public reporting tied its use to targeted campaigns (including Russian SVR-linked operations), though no public proof-of-concept is known.

What to do: Update devices to iOS 12.5.2 (older devices) or iOS 14.4.2/iPadOS 14.4.2, and Apple Watch devices to watchOS 7.3.3, per Apple's instructions. Because exploitation requires loading malicious web content in WebKit, avoid following untrusted web links on unpatched devices until updated; verify fleet-wide OS versions and confirm the fix, since this CVE is on the CISA KEV catalog with patching required. Check logs or browser history for signs of visits to attacker-controlled sites on devices that have since been updated, as no public proof-of-concept exists to test against.