CVE-2021-1870

CVE-2021-1870 is a logic flaw in Apple's WebKit browser engine, addressed in iOS 14.4, iPadOS 14.4, macOS Big Sur 11.2, and Security Update 2021-001 for Catalina and Mojave via improved restrictions. A remote attacker can trigger the flaw through hostile web content processed by WebKit on a vulnerable device, with no authentication or privileges required per the CVSS 3.1 network-vector scoring. Successful exploitation allows arbitrary code execution on the affected device. All users of iPhone OS/iPadOS prior to 14.4 and macOS prior to the listed fixes are affected, as WebKit ships with every Apple device, and WebKitGTK/Fedora users of the same engine are also potentially impacted. Apple reported the issue may have been actively exploited in the wild as a zero-day, and CISA added it to the Known Exploited Vulnerabilities catalog on 2021-11-03.

What to do: Upgrade iPhones/iPads to iOS/iPadOS 14.4, Macs to macOS Big Sur 11.2, and apply Security Update 2021-001 on Catalina and Mojave. Fedora/WebKitGTK users should install the distribution's updated WebKitGTK packages. The issue is on the CISA KEV list with a required action of applying vendor updates; no public PoC or specific mitigation is known, so patching is the primary remediation.