CVE-2026-84536 in macOS
Summary
by MITRE • 09/15/2026
An integer underflow was addressed with improved input validation. 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 integer underflow within the Server Message Block protocol implementation on Apple operating systems, specifically affecting versions prior to macOS Golden Gate 27, macOS Sequoia 15.8, and macOS Tahoe 26.7. Integer underflows occur when a subtraction operation results in a value smaller than the minimum representable value for the data type used. In this context, improper input validation allows an attacker-controlled SMB server to supply values that cause arithmetic operations within the client-side SMB stack to wrap around negatively or incorrectly. This flaw is categorized under CWE-192, which defines integer coercion errors where a numeric value is converted to another numeric type inappropriately, often leading to unexpected behavior such as buffer overflows, logic errors, or denial of service conditions.
The operational impact of this vulnerability is significant due to the nature of network protocol handling. When an Apple device connects to a malicious SMB server crafted with specific malformed packets that trigger the integer underflow, the system fails to handle the resulting invalid state correctly. Instead of gracefully rejecting the request or isolating the error, the underlying kernel or networking subsystem encounters a critical exception. This leads to unexpected system termination, effectively causing a denial of service against the local machine. For users relying on file sharing and network connectivity, this means that simply connecting to an untrusted SMB share can result in immediate system crashes, requiring a reboot and potentially leading to data loss if unsaved work was active at the time of the crash.
From a threat intelligence perspective, this vulnerability aligns with ATT&CK technique T1499, Endpoint Denial of Service, where adversaries aim to exhaust or degrade resources on an endpoint. While often exploited for disruption rather than direct code execution in its initial form, such crashes can sometimes be chained with other vulnerabilities to achieve remote code execution if the memory corruption state allows for arbitrary write primitives. The lack of robust input validation at the protocol parsing stage highlights a common weakness in network stack implementations where performance optimizations may have bypassed necessary bounds checking or type safety verifications.
Mitigation requires immediate patching by updating macOS systems to Golden Gate 27, Sequoia 15.8, or Tahoe 26.7 or later versions. These updates include the corrected input validation logic that properly checks for potential underflow conditions before performing arithmetic operations on SMB packet data. Until patches are applied, administrators should restrict access to SMB services by configuring firewalls to block inbound and outbound traffic to untrusted networks. Additionally, disabling unnecessary file sharing features reduces the attack surface. Security teams should monitor network logs for anomalous SMB connection attempts from unknown sources as a defensive measure against exploitation of this specific flaw in unpatched environments.