CVE-2026-84509 in macOS
Summary
by MITRE • 09/15/2026
An out-of-bounds read was addressed with improved bounds checking. This issue is fixed in macOS Golden Gate 27, macOS Sequoia 15.8, macOS Tahoe 26.7. Connecting to a malicious SMB server may lead to unexpected system termination.
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Analysis
by VulDB Data Team • 09/15/2026
The vulnerability described involves an out-of-bounds read within the Server Message Block (SMB) client implementation on Apple operating systems. This type of flaw typically arises when software fails to properly validate input data before accessing memory locations, allowing a process to read beyond the intended buffer boundaries. In this specific instance, the issue was addressed by implementing improved bounds checking mechanisms that ensure all memory accesses remain within allocated and valid limits. The root cause lies in insufficient validation of packet structures or field lengths received from remote SMB servers, which is a common attack vector for network-facing services. By failing to verify that requested data sizes do not exceed buffer capacities, the application could trigger an illegal memory access when processing specially crafted packets designed to exploit this boundary condition.
The operational impact of this vulnerability centers on system stability and availability rather than direct code execution or privilege escalation in its current manifestation. Connecting to a malicious SMB server can lead to unexpected system termination, effectively resulting in a denial-of-service condition for the affected macOS device. When an attacker sends malformed packets that trigger the out-of-bounds read, it causes the operating system's kernel or network stack to encounter an unrecoverable error, leading to a crash or reboot of the machine. This disrupts any ongoing file sharing operations and can cause data loss if unsaved work is present on systems relying on SMB connections for storage access. The severity is heightened by the fact that it requires only a connection initiation from the victim side, making remote exploitation feasible without user interaction beyond establishing network connectivity to the malicious host.
From a classification perspective, this vulnerability aligns with CWE-125, which defines out-of-bounds read errors where software reads data past the end or before the beginning of the intended buffer. It also relates to CWE-20, improper input validation, as the core failure is the lack of rigorous checks on external data integrity and size constraints. In terms of adversarial tactics, this exploit scenario maps to MITRE ATT&CK technique T1499, Endpoint Denial of Service, specifically under subcategories involving resource exhaustion or service disruption through application crashes. The attack vector falls under Network-Based exploitation (T1078) if the SMB server is part of an authenticated session setup phase, though it primarily functions as a remote denial-of-service mechanism via protocol manipulation rather than authentication bypass.
Mitigation strategies for this vulnerability involve applying the provided software updates to macOS Golden Gate 27, macOS Sequoia 15.8, and macOS Tahoe 26.7 immediately upon availability. These patches contain the necessary code changes to enforce strict bounds checking on SMB packet processing routines. Until updates are applied, administrators should restrict access to SMB services by configuring firewalls to block incoming connections from untrusted networks or specific IP addresses known to be malicious. Additionally, disabling unnecessary SMB client functionality if not required for business operations can reduce the attack surface. Organizations should also implement network monitoring solutions capable of detecting anomalous SMB traffic patterns that deviate from standard protocol behavior, which may indicate an attempt to exploit this vulnerability before patches are deployed. Regular security audits and penetration testing focused on file sharing protocols can help identify similar implementation flaws in other legacy systems within the enterprise environment.