CVE-2026-23850 is a path traversal vulnerability classified under CWE-22 affecting the SiYuan Note personal knowledge management system. The issue exists in versions prior to 3.5.4 where the markdown feature permits unrestricted server-side HTML rendering. This improper limitation of pathname input allows attackers to craft malicious markdown content that causes the server to read arbitrary files on the host filesystem. The vulnerability requires no authentication or user interaction, making it remotely exploitable over the network. The CVSS 4.0 vector (AV:N/AC:L/AT:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N/E:P) reflects that an attacker can exploit this with low complexity and no privileges, resulting in high confidentiality impact due to local file disclosure. Integrity and availability impacts are low to none. The vulnerability was publicly disclosed on January 19, 2026, with no known exploits in the wild at the time. The fix was introduced in version 3.5.4 by restricting the markdown rendering process to prevent arbitrary file reads. This vulnerability is critical for environments where sensitive data is stored on systems running vulnerable SiYuan Note versions, as attackers could access configuration files, credentials, or other private information.

For European organizations, the primary impact is the potential exposure of sensitive internal files, including credentials, configuration files, or proprietary documents stored on systems running vulnerable SiYuan Note versions. This could lead to information disclosure, facilitating further attacks such as lateral movement or privilege escalation. Since the vulnerability requires no authentication and no user interaction, it could be exploited remotely by attackers scanning for vulnerable instances. Organizations using SiYuan Note for knowledge management in sectors such as finance, healthcare, or government could face significant confidentiality breaches. The impact on integrity and availability is minimal, but the loss of confidentiality alone can have severe regulatory and reputational consequences under GDPR and other data protection laws. Additionally, attackers could leverage disclosed data to mount more sophisticated attacks against European targets.

1. Immediately upgrade all SiYuan Note installations to version 3.5.4 or later, which contains the patch for this vulnerability. 2. Restrict file system permissions for the SiYuan Note application user to the minimum necessary, preventing access to sensitive directories and files. 3. Implement network-level access controls to limit exposure of SiYuan Note services to trusted internal networks or VPNs. 4. Monitor application logs and file access patterns for unusual or unauthorized file read attempts, especially those involving sensitive system files. 5. Conduct regular vulnerability scans and penetration tests focusing on path traversal and local file inclusion vulnerabilities. 6. Educate users and administrators about the risks of running outdated software and the importance of timely patching. 7. If upgrading immediately is not feasible, consider disabling the markdown feature or server-side HTML rendering temporarily as a stopgap measure.