Apple fixes actively exploited WebKit zero-day (CVE-2024-23222)

CVE-2023-42917 is a memory corruption flaw (CWE-787, out-of-bounds write class) in Apple's WebKit browser engine, addressed with improved locking. It is triggered when a device processes maliciously crafted web content, meaning an attacker can reach vulnerable code simply by getting a user to load attacker-controlled web content. Successful exploitation may lead to arbitrary code execution with the privileges of the affected application. All users of the affected Apple platforms — iPhone, iPad, Mac (Sonoma), and Safari — are exposed, and the CPE data also indicates WebKitGTK as shipped by Debian and Fedora is in scope. The flaw is being actively exploited: Apple reported it was exploited in the wild against versions of iOS before 16.7.1, it was added to CISA KEV on 2023-12-04, and EPSS assigns a 9.4% probability of exploitation in the next 30 days (95th percentile).

Do: Upgrade to iOS 17.1.2, iPadOS 17.1.2, macOS Sonoma 14.1.2, and Safari 17.1.2; organizations with devices on the older iOS 16 line should check Apple's advisories for backported fixes, since the in-the-wild exploitation was reported against iOS versions before 16.7.1. Linux defenders running Debian or Fedora should apply the latest WebKitGTK security updates from their distribution. As a KEV entry (added 2023-12-04), remediation is mandatory for federal agencies per CISA's required action; verify device versions via MDM or inventory and prioritize internet-facing and high-risk users.

CVE-2024-23222 is a type confusion flaw (CWE-843) in Apple's WebKit engine that allows arbitrary code execution when a device processes maliciously crafted web content, for example when a user is lured into loading attacker-controlled web pages in Safari or another WebKit-based view (the CVSS vector confirms user interaction is required). It affects a broad slice of the Apple ecosystem: Safari, iPhone OS/iPadOS on the iOS 15, 16 and 17 branches, macOS Monterey/Ventura/Sonoma, tvOS and visionOS, prior to the January 22, 2024 fixes. A successful attacker gains code execution on the target device with high impact on confidentiality, integrity and availability (CVSS 3.1: 8.8). The flaw was fixed in Safari 17.3, iOS/iPadOS 17.3, and backported to iOS/iPadOS 15.8.7 and 16.7.5 for devices that cannot upgrade to iOS 17, plus macOS Monterey 12.7.3, Ventura 13.6.4, Sonoma 14.3, tvOS 17.3 and visionOS 1.0.2. Exploitation is confirmed in the wild: the vulnerability was added to CISA KEV on 2024-01-23, one day after the fixes shipped, and is associated with the Coruna exploit kit, which reportedly chains multiple exploits to target iOS devices including older versions.

Do: Update all affected devices to Safari 17.3, iOS/iPadOS 17.3 (or the iOS/iPadOS 15.8.7 and 16.7.5 backports for devices that cannot run 17), macOS Monterey 12.7.3, macOS Ventura 13.6.4, macOS Sonoma 14.3, tvOS 17.3 and visionOS 1.0.2. Prioritize endpoints used for web browsing and mobile users, since exploitation only requires a user to process crafted web content. The CISA KEV listing (added 2024-01-23) makes applying these vendor updates mandatory under the KEV required action, so verify fleet versions and confirm no devices remain on pre-patch builds.