CVE-2026-86926 in FileMaker Server
Summary
by MITRE • 09/23/2026
A heap buffer overflow vulnerability in the FileMaker Server database engine block parsing routine allowed a maliciously crafted .fmp12 database file to cause memory corruption, potentially leading to arbitrary code execution. This vulnerability is addressed in FileMaker Server version 26.0.3.
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Analysis
by VulDB Data Team • 09/23/2026
The identified security flaw resides within the core database engine of FileMaker Server, specifically affecting the routine responsible for parsing block structures in .fmp12 files. As a heap buffer overflow vulnerability, this issue stems from improper validation of boundary conditions when processing input data derived from maliciously crafted database files. When an attacker provides a specially constructed .fmp12 file with malformed or excessively large block headers and payloads, the application fails to correctly calculate memory allocation sizes or check array bounds before writing data to the heap. This discrepancy allows write operations to extend beyond the allocated buffer boundaries into adjacent memory regions. Such out-of-bounds writes can corrupt critical metadata structures within the heap manager, such as free lists or size fields, which are essential for maintaining memory integrity during runtime execution.
The operational impact of this vulnerability is severe due to its potential to lead to arbitrary code execution. By carefully crafting the overflow payload, an attacker can overwrite function pointers, return addresses, or other control flow data stored in adjacent heap chunks. This manipulation enables the injection and subsequent execution of shellcode within the context of the FileMaker Server process. Since database servers typically run with elevated privileges to manage sensitive organizational data, successful exploitation could grant a remote unauthenticated attacker full control over the underlying operating system. The attack vector is primarily network-based if the server exposes file upload or import functionalities that accept .fmp12 files without rigorous sanitization, allowing for remote code execution without user interaction beyond providing the malicious file input.
From a classification perspective, this vulnerability aligns with CWE-122, which denotes heap-based buffer overflow, and is associated with ATT&CK technique T1059, specifically command scripting or binary executable injection depending on the final payload delivery mechanism. The lack of proper bounds checking during data parsing represents a fundamental input validation failure that compromises memory safety guarantees inherent in modern software development practices. To mitigate this risk, organizations must immediately apply the vendor-provided patch by upgrading to FileMaker Server version 26.0.3 or later, which includes corrected logic for validating block sizes and ensuring safe memory allocation limits during parsing operations. Additionally, implementing strict file type validation on all endpoints that accept database imports can reduce the attack surface. Network-level controls such as web application firewalls should be configured to inspect incoming files for anomalies in structure size relative to expected norms, although reliance solely on perimeter defenses is insufficient given the complexity of modern exploit development techniques. Regular security audits and static code analysis focused on memory management routines are recommended to prevent similar vulnerabilities from being introduced into custom integrations or extensions that interact with the core database engine.