CVE-2026-43719 in macOS
Summary
by MITRE • 09/15/2026
A use-after-free issue was addressed with improved memory management. This issue is fixed in macOS Golden Gate 27, macOS Sequoia 15.8, macOS Tahoe 26.7. Mounting a maliciously crafted SMB network share may lead to system termination.
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Analysis
by VulDB Data Team • 09/15/2026
The vulnerability described involves a use-after-free error within the Server Message Block (SMB) client implementation in Apple's operating systems, specifically affecting versions prior to macOS Golden Gate 27, macOS Sequoia 15.8, and macOS Tahoe 26.7. A use-after-free is a critical memory corruption flaw that occurs when software continues to use a pointer after the memory it points to has been freed or deallocated. In this context, the SMB client fails to properly manage the lifecycle of certain data structures associated with network share connections. When an attacker mounts a maliciously crafted SMB network share, they can trigger specific code paths that cause the system to free memory resources while references to those same resources are still active within the application's execution flow. Subsequent operations attempting to access these dangling pointers result in undefined behavior, which Apple has identified as leading directly to system termination or crash conditions.
From a technical perspective, this flaw represents a failure in proper resource management and boundary checking during network protocol processing. The SMB protocol is widely used for file sharing across networks, making it a common attack surface. By crafting a specially designed SMB response or packet sequence, an attacker can manipulate the internal state of the SMB client to force premature deallocation of critical memory blocks. When the application later attempts to read from or write to these freed addresses, it may cause immediate crashes due to segmentation faults or access violations. While modern operating systems employ various mitigations such as Address Space Layout Randomization (ASLR) and Data Execution Prevention (DEP), use-after-free vulnerabilities remain particularly dangerous because they can sometimes be leveraged for arbitrary code execution if the attacker can control the content written into the freed memory region before it is reallocated, although in this specific instance, the primary observed impact is system termination.
The operational impact of this vulnerability centers on availability and potential stability issues for users connecting to untrusted or compromised SMB servers. An attacker with network access who hosts a malicious SMB share can cause denial-of-service conditions by triggering repeated crashes of the affected macOS processes or even full system reboots if kernel-level memory corruption occurs. This disrupts productivity and may lead to data loss if unsaved work is lost during unexpected terminations. Furthermore, while the immediate symptom described is termination, use-after-free vulnerabilities are historically among the most prevalent causes of remote code execution exploits in network services. Security researchers often view such flaws as potential gateways for more severe compromises, including privilege escalation or full system takeover, depending on how the freed memory is reused and whether additional exploitation techniques can be applied to stabilize the crash into a controlled execution state.
To mitigate this risk, administrators and users should ensure that all macOS devices are updated to at least macOS Golden Gate 27, Sequoia 15.8, or Tahoe 26.7, where Apple has implemented improved memory management routines to correctly track pointer lifecycles and prevent access to freed memory. In environments where SMB sharing is not required, disabling the service reduces the attack surface significantly. When connecting to external network shares, users should exercise caution regarding untrusted sources and consider using virtualized or sandboxed environments for testing unknown share contents. From a defensive engineering standpoint, this incident highlights the importance of rigorous static analysis and fuzzing during software development to detect memory management errors early in the lifecycle. Industry standards such as CWE-416 (Use After Free) categorize this flaw type due to its prevalence and severity, while ATT&CK techniques related to resource hijacking or denial-of-service may apply depending on the attacker's ultimate objective beyond mere disruption.