CVE-2026-43734: Apple Safari Use-After-Free Memory Vulnerability

Technical summary

CVE-2026-43734 is a use-after-free vulnerability (CWE-416) in Apple's WebKit rendering engine and Safari browser. Use-after-free occurs when code attempts to access memory that has already been freed, typically resulting in a crash but occasionally exploitable for code execution if an attacker can control heap layout and post-free allocation patterns. This particular instance was remediated through improved memory management in Safari 26.5.2, iOS 26.5.2, iPadOS 26.5.2, macOS Tahoe 26.5.2, tvOS 26.6, visionOS 26.6, and watchOS 26.6. The CVSS 3.1 vector indicates network-accessible attack surface, low attack complexity, no privileges required, but user interaction necessary; impact is limited to availability (process crash).

Business impact

End-user disruption dominates the business impact. Employees browsing untrusted or compromised websites may experience Safari crashes, interrupting work and potentially causing data loss if unsaved work was in progress. For organizations where Safari is a primary browser on iOS/macOS devices, widespread crashes could reduce productivity. The vulnerability does not enable authentication bypass, data exfiltration, or lateral movement, so enterprise infrastructure integrity remains unaffected. Customer-facing web services are not directly at risk unless they serve malicious content to their own users.

Affected systems

Apple Safari across macOS Tahoe and earlier versions; Apple iOS (iPhone) through version 26.5.1; Apple iPadOS through version 26.5.1; tvOS through version 26.5; visionOS through version 26.5; and watchOS through version 26.5. Any organization deploying these platforms, particularly in bring-your-own-device (BYOD) or corporate device programs, has exposure. Desktop Safari users and mobile users on iPhones/iPads are most affected due to their active web browsing patterns.

Exploitability

Exploitation requires crafting malicious web content and either hosting it or injecting it into a legitimate website or ad network. User interaction is mandatory—the victim must visit the malicious page, which lowers the exploitability bar compared to zero-click attacks but still presents a credible threat in targeted campaigns or opportunistic compromises of high-traffic sites. The vulnerability is not currently listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, suggesting active exploitation in the wild has not been widely documented at time of publication, though absence from KEV does not guarantee safety. Code execution potential is not confirmed; the documented impact is denial of service via process crash.

Remediation

Apply the following patches immediately: Safari 26.5.2 (macOS), iOS 26.5.2, iPadOS 26.5.2, macOS Tahoe 26.5.2, tvOS 26.6, visionOS 26.6, and watchOS 26.6. Organizations should prioritize patching user-facing devices where employees browse untrusted web content. Enable automatic updates where policy permits to reduce manual deployment overhead. For managed environments, coordinate patch deployment with standard update cycles to minimize disruption.

Patch guidance

Verify the specific version numbers against Apple's official security advisory to ensure you deploy the correct build. iOS, iPadOS, and macOS updates are delivered through standard system update mechanisms (Settings > General > Software Update on iOS/iPadOS, System Settings > General > Software Update on macOS). Safari on macOS updates alongside the operating system. For tvOS, visionOS, and watchOS, patches are similarly delivered through native update pathways. Test patches in a non-production environment if managing a large fleet, particularly if you have custom enterprise web applications or plugins. Monitor update progress using Mobile Device Management (MDM) solutions if deployed.

Detection guidance

Monitor system logs and crash reports for Safari process terminations (Safari, WebKit child processes) that correlate with web browsing activity. On macOS, examine system.log for unexpected Safari exits. On iOS/iPadOS, collect diagnostic data from affected devices through MDM or Apple Configurator if available. Network-based detection is limited since the attack surface is the legitimate browser rendering engine; however, intrusion detection systems could flag known-malicious domains or suspicious ad networks if you have visibility into DNS or web proxy logs. Encourage users to report unexpected browser crashes, which may indicate attempted exploitation.

Why prioritize this

Patch this vulnerability in the normal monthly update cycle rather than as an emergency. The CVSS score of 6.5 (MEDIUM) reflects that user interaction is required and the impact is limited to availability. The lack of confirmed active exploitation and absence from the KEV catalog further lower urgency. However, prioritize patching for staff in high-risk roles (journalists, activists, security researchers) who may be targeted by sophisticated threat actors who craft custom malicious pages.

Risk score, explained

The CVSS 3.1 score of 6.5 (MEDIUM severity) combines a low-barrier attack vector (network-accessible, low complexity) with a high-impact consequence (availability) but gates exploitation behind mandatory user interaction and yields only a crash, not code execution. The vector CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H reflects: AV:N (network attack), AC:L (low complexity), PR:N (no privileges), UI:R (user interaction required), S:U (scope unchanged), C:N (no confidentiality loss), I:N (no integrity loss), A:H (high availability impact). This is not a critical vulnerability but warrants timely remediation to prevent user disruption.

Frequently asked questions