External risk intelligence

macOS Out-of-Bounds Write Allows Unexpected System Termination.

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2026-43748

This vulnerability affects local macOS system components. Such components are typically part of the operating system's internal architecture, requiring local access or specific application-level interaction rather than being exposed as a public-facing network service or internet-accessible gateway.

Out-of-bounds Write

Apple Macos

15.0 to before 15.7.826.0 to before 26.6

Halo Surface Signal: 1 out of 5 — much less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

This advisory concerns an out-of-bounds write vulnerability in macOS. While the specifics of exploitation are not detailed here, the issue could potentially lead to unexpected system termination, impacting the stability of affected systems. The main concern at this stage is confirming relevance and exposure.

Allows apps to crash macOS systems.
Stability risk; confirm if systems are updated.
Monitor for and confirm relevance of exposure.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by sending specially crafted data to a vulnerable application. This could lead to an unexpected termination of the system.

Requires network access.
Triggered by sending crafted data.
Can cause system termination.

Live Threat

Current exploitation, exposure, and threat context

An out-of-bounds write could allow an application to cause unexpected system termination. This could occur when an application, without requiring user interaction or elevated privileges, triggers this issue, potentially leading to instability.

System stability and availability.
Unexpected termination of applications or the OS.
Disruption of normal system operations.

Operational Fix

Recommended remediation, mitigation, and detection steps

Determining precise ownership requires understanding your macOS deployment model and asset management practices. Initially, focus on identifying all macOS systems, assessing their exposure and criticality, and locating the accountable system owner. This will inform a prioritized remediation plan.

Identify affected macOS systems and owners.
Verify system reachability and business criticality.
Plan remediation based on identified risk.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is macOS Sequoia and Tahoe?

These are versions of the Apple macOS operating system. They act as the foundational software platform that manages hardware resources and runs applications. This CVE specifically identifies issues within the core system components of macOS Sequoia 15.7.7 and earlier, as well as macOS Tahoe 26.5 and earlier, which require these updates to maintain proper system memory management.

What does an out-of-bounds write mean in CVE-2026-43748?

This vulnerability, classified as CWE-787, occurs when software writes data past the intended boundary of a memory buffer. Think of it like a filing clerk placing a document on the floor because the drawer is full. Because the system does not properly check memory limits, this misplaced data can corrupt adjacent memory, leading the operating system to terminate unexpectedly to prevent further instability.

How is this vulnerability triggered?

An attacker triggers this by sending specially crafted data to a vulnerable application or service. It is important to note that simply using the computer for standard tasks does not trigger the bug; the system must process specific, malicious input designed to exploit the missing bounds check. Without this specific interaction, the memory error does not occur.

Is my system at risk from internet attacks?

According to Halo Surface Signal, this is very unlikely. While the vulnerability is classified as having a network attack vector, it impacts internal macOS system components that are not typically exposed as public-facing gateways. Most users will find these components are shielded by the operating system's architecture, requiring direct interaction rather than being reachable from the open internet.

Do I need to update my macOS devices?

Yes. The most effective way to address this is to ensure your systems are running macOS Sequoia 15.7.8, macOS Tahoe 26.6, or a later version. Start by inventorying your devices to identify which are running affected versions. Once identified, prioritize these systems for an operating system update to implement the improved bounds checking provided by Apple.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.