CVE-2026-109309 in SiYuan
Summary
by MITRE • 10/12/2026
SiYuan v3.7.0 before v3.8.6 contains an absolute path traversal vulnerability in the kernel's private plugin HTTP server, which passes a kernel plugin handler's ResponseFile.Path to gin's Context.File without validation. Attackers supplying a malicious kernel plugin can return an absolute path to read any file readable by the SiYuan process, including the API token and conf.json.
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Analysis
by VulDB Data Team • 10/12/2026
The vulnerability identified in SiYuan versions prior to 3.8.6 represents a critical security flaw within the application's private plugin HTTP server architecture. This issue stems from an absolute path traversal weakness that allows unauthorized access to sensitive files on the host system. The core of the problem lies in how the kernel handles responses generated by plugins, specifically regarding file serving operations. When a kernel plugin handler returns a response containing a file path via the ResponseFile.Path field, this value is passed directly to the gin web framework's Context.File method without any form of validation or sanitization. This lack of input verification creates a direct vector for attackers to manipulate file system access controls through maliciously crafted plugins.
From a technical perspective, the flaw exploits the trust relationship between the SiYuan kernel and its plugin ecosystem. Plugins are designed to extend functionality, but in this instance, the mechanism used to serve files back to users fails to enforce boundary constraints on the provided path. By supplying an absolute path rather than a relative one within a malicious kernel plugin, an attacker can bypass intended directory restrictions. The gin framework, which serves as the underlying HTTP server for these operations, will attempt to read and transmit whatever file path is specified in the request payload. Since there are no checks to ensure the path remains within the allowed application directories or does not escape into sensitive system areas, the vulnerability effectively neutralizes standard web security models that rely on directory isolation.
The operational impact of this vulnerability is severe due to the high privileges typically held by desktop applications like SiYuan. An attacker who can execute a malicious kernel plugin gains the ability to read any file accessible by the user account running the SiYuan process. This includes critical configuration files such as conf.json, which often contains database connection strings and other sensitive settings, as well as API tokens that authenticate sessions with external services or internal endpoints. The exposure of these credentials can lead to full account compromise, unauthorized data access, and potential lateral movement if those tokens are reused across other systems. This scenario aligns closely with CWE-22, which defines Improper Limitation of a Pathname to a Restricted Directory, as the application fails to restrict file operations to intended locations.
Furthermore, this vulnerability facilitates actions consistent with ATT&CK technique T1083, File and Directory Discovery, allowing adversaries to enumerate sensitive system resources. It also supports data exfiltration capabilities described in techniques such as T1567, Exfil Over Web Service, if the retrieved files are transmitted out of band through subsequent plugin interactions or HTTP responses. The severity is amplified by the fact that kernel plugins often run with elevated privileges compared to standard user-space applications, meaning the scope of accessible files extends beyond typical application data to include system-level configurations and personal documents stored in local directories.
Mitigation strategies must focus on immediate patching and architectural hardening. Users should upgrade SiYuan to version 3.8.6 or later, where this path traversal issue has been addressed by implementing proper validation logic before passing file paths to the HTTP server components. In environments where upgrading is not immediately feasible, restricting plugin installation sources to only trusted developers can reduce exposure risk. Additionally, running the application with least-privilege principles ensures that even if a vulnerability is exploited, the attacker's ability to access sensitive system files is limited by operating system permissions. Future development should enforce strict allow-listing of file paths and utilize secure APIs for serving static content rather than passing raw path strings directly into web framework handlers without sanitization checks.