CVE-2026-84549 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 NFS server may cause unexpected system termination or corrupt kernel memory.
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Analysis
by VulDB Data Team • 09/15/2026
The vulnerability described involves an out-of-bounds read within the Network File System client implementation in Apple operating systems, specifically affecting versions prior to macOS Golden Gate 27, macOS Sequoia 15.8, and macOS Tahoe 26.7. This flaw is categorized under CWE-125, which defines Out-of-Bounds Read as a memory safety issue where software reads data beyond the intended buffer boundary. In the context of network file systems, such errors often arise when parsing or processing incoming packets from remote servers without adequate validation of packet lengths against allocated buffer sizes. The root cause lies in insufficient bounds checking during the handling of NFS protocol responses, allowing an attacker to craft maliciously sized or malformed data structures that trigger memory access violations outside the designated kernel space boundaries.
From a technical perspective, this vulnerability exploits the trust relationship between the client and the server within the NFS protocol stack. When a macOS device connects to an NFS share, it processes various metadata and file content responses from the remote server. If the server sends data exceeding the expected limits for specific internal buffers used by the kernel's network stack or filesystem driver, the lack of rigorous boundary verification leads to reading arbitrary memory locations. This behavior is particularly dangerous because it occurs in kernel space, where memory protection mechanisms are less granular than in user-space applications. The ability to read beyond allocated bounds can lead to information disclosure if sensitive data residing adjacent to the buffer is leaked into application-visible areas or logged structures.
The operational impact of this vulnerability extends beyond simple information leakage. As noted in the advisory, connecting to a malicious NFS server may cause unexpected system termination, commonly known as a kernel panic or denial of service. This occurs when the out-of-bounds read accesses memory regions that are protected or unmapped, triggering an immediate fault exception handled by the operating system's crash handler. In more severe scenarios, depending on how the leaked data is subsequently processed or if combined with other exploitation techniques, it could potentially lead to kernel memory corruption. Such corruption can destabilize the entire system, leading to unpredictable behavior, loss of unsaved work, and complete service interruption for all users on the affected device.
This vulnerability aligns with MITRE ATT&CK technique T1083, File and Directory Discovery, as an out-of-bounds read in a file system driver can be leveraged to enumerate or access restricted files that should not be visible to the connecting user or process. Furthermore, it relates to CWE-200, Exposure of Sensitive Information to an Unauthorized Actor, due to the potential for leaking kernel memory contents which may contain cryptographic keys, session tokens, or other sensitive operational data. The attack vector is classified as Network-based with a requirement for Local User interaction only in terms of initiating the connection, but the actual exploitation requires the user or automated process to connect to a hostile NFS server, making it an Attack Vector that relies on social engineering or compromised network infrastructure rather than direct local access.
Mitigation strategies primarily involve applying the provided software updates from Apple, which introduce improved bounds checking logic within the NFS client implementation. These patches ensure that all incoming data lengths are validated against buffer capacities before processing begins, thereby preventing any attempt to read beyond allocated memory regions. Administrators should also enforce strict network segmentation policies to restrict access to internal file shares and avoid connecting macOS devices to untrusted or public NFS servers whenever possible. Additionally, implementing deep packet inspection at the network perimeter can help identify anomalous NFS traffic patterns that might indicate an attempted exploitation of this vulnerability. Regular patch management cycles are critical to ensuring that systems remain protected against such memory safety issues as new updates become available for all supported macOS versions.