Apple patches iOS 12 after hackers exploit WebKit Engine flaws

A blue model of the iPhone 12 Pro
(Image credit: Shutterstock)

Apple has released an out-of-band security fix to address two zero-day vulnerabilities in iOS 12.5.3 that hackers are actively exploiting to launch remote code execution attacks.

The two flaws under scrutiny are CVE-2021-30761 and CVE-2021-30762, which both lie in the open source WebKit browser rendering engine used by Apple to power Safari, as well as all iOS web browsers. It’s also used by many other apps across the Apple ecosystem on various devices.

Apple has patched these two flaws with iOS version 12.5.4, alongside a fix for a memory corruption issue in ASN.1 decoder, tracked as CVE-2021-30737. Abstract Syntax Notation One, or ASN.1, is a standard interface language for defining data structures that can be serialised and deserialised in a cross-platform way.

The first of the two WebKit flaws, CVE-2021-30761, is also a memory corruption issue that can be exploited to execute code remotely when processing malicious web content.

The second, CVE-2021-30762, is a use-after-free issue that can also be exploited to launch remote code execution attacks when processing malicious content.

They’ve been fixed with “improved state management” and “improved memory management” respectively.

These two are only the latest flaws to affect Apple’s WebKit browser engine that hackers have exploited since the start of the year. In total, Apple has patched seven WebKit-related flaws since January 2021, across various devices.


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WebKit, alongside its use in Safari, is also used in various iOS, macOS, watchOS and Apple TV apps and services.

The latest version of Safari released in April brought with it a host of new WebKit features, APIs, performance improvements and better compatibility for web developers. For example, Safari 14.1 now supports a media encoder as well as date and time inputs on macOS.

Support for the AudioWorklets technology, a web standard that optimises audio processing in the browser, however, brought with it a glaring security issue.

Researchers with Theori reported that a bug in the implementation of this feature made it possible to use technology to get Safari and other WebKit-based browsers to run arbitrary code. Although the WebKit developers fixed the bug, Apple’s Safari developers didn’t bake this into the web browser on iOS or macOS.

Keumars Afifi-Sabet

Keumars Afifi-Sabet is a writer and editor that specialises in public sector, cyber security, and cloud computing. He first joined ITPro as a staff writer in April 2018 and eventually became its Features Editor. Although a regular contributor to other tech sites in the past, these days you will find Keumars on LiveScience, where he runs its Technology section.