CVE-2026-25992 in SiYuan
Summary
by MITRE • 02/10/2026
SiYuan is a personal knowledge management system. Prior to 3.5.5, the /api/file/getFile endpoint uses case-sensitive string equality checks to block access to sensitive files. On case-insensitive file systems such as Windows, attackers can bypass restrictions using mixed-case paths and read protected configuration files. This vulnerability is fixed in 3.5.5.
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Analysis
by VulDB Data Team • 02/10/2026
The vulnerability described in CVE-2026-25992 affects SiYuan, a personal knowledge management system that has been widely adopted for organizing and storing sensitive information. This issue represents a classic access control flaw that exploits differences in file system behavior between operating systems. The vulnerability exists in versions prior to 3.5.5 where the system implements a security mechanism to prevent unauthorized access to sensitive files through the /api/file/getFile endpoint.
The technical flaw manifests as a case-sensitive string equality check that fails to properly account for file system characteristics. When the application performs access control checks, it compares user-provided file paths against a list of restricted files using exact case-sensitive matching. This approach works correctly on case-sensitive file systems such as Linux or macOS, but becomes ineffective on case-insensitive file systems like Windows. The vulnerability stems from the application's assumption that file path comparisons will behave consistently across different operating environments, which is not the case in practice.
On Windows systems, where file names are case-insensitive, attackers can exploit this weakness by crafting file paths using mixed-case characters that match the intended restricted file names. For example, if a configuration file named "config.json" is protected, an attacker could request a file using a path like "Config.JSON" or "CONFIG.Json" to bypass the security check. This technique relies on the fact that while the application performs case-sensitive comparisons against its internal list of blocked files, the actual file system allows access to files regardless of case variations.
The operational impact of this vulnerability is significant for users who store sensitive configuration data, authentication tokens, or other confidential information within their SiYuan knowledge base. Attackers who can successfully bypass these access controls gain unauthorized access to protected configuration files that may contain database connection strings, API keys, encryption keys, or other credentials that could compromise the entire system. The vulnerability essentially provides a path for lateral movement and privilege escalation within the application's security model, potentially allowing attackers to access not just individual files but also to understand the application's internal structure and data organization.
This vulnerability aligns with CWE-284, which describes improper access control, and demonstrates how system-level differences can create security gaps in applications designed primarily for cross-platform compatibility. The flaw also relates to ATT&CK technique T1213.002, which involves data from information repositories, and T1566.001, which covers spearphishing with attachments, as the vulnerability could enable attackers to obtain sensitive data that might be used for further attacks. The issue highlights the importance of considering platform-specific behaviors when implementing security controls, particularly in applications that are intended to run across multiple operating systems.
The mitigation for this vulnerability involves upgrading to SiYuan version 3.5.5 or later, which addresses the issue by implementing proper case-insensitive path comparison mechanisms. Additionally, system administrators should review their security configurations and ensure that all file access controls are implemented using consistent case handling regardless of the underlying file system. Organizations should also implement additional monitoring and logging of file access attempts to detect potential exploitation attempts. The fix should include normalizing file paths to a consistent case before performing access control checks, ensuring that the security mechanism functions correctly across all supported platforms.