Trilium Notes is an open-source, cross-platform hierarchical note-taking application designed for building large personal knowledge bases. The vulnerability CVE-2025-68621 arises from a timing attack vector in the sync authentication endpoint prior to version 0.101.0. Specifically, the implementation of HMAC authentication leaks timing information that can be measured by an attacker remotely without authentication or user interaction. By statistically analyzing the response times byte-by-byte, an attacker can recover the HMAC authentication hash, effectively bypassing authentication controls. This allows the attacker to gain full read and write access to the victim's knowledge base, compromising confidentiality and integrity of stored data. The vulnerability is categorized as CWE-208, indicating an observable timing discrepancy that leaks sensitive information. The CVSS v3.1 base score is 7.4 (high), reflecting the network attack vector, no privileges required, no user interaction, and high impact on confidentiality and integrity, though availability is unaffected. The flaw was publicly disclosed and fixed in Trilium version 0.101.0. No public exploits have been reported yet, but the ease of remote exploitation and critical impact make this a significant threat for users of affected versions.

For European organizations using Trilium Notes versions prior to 0.101.0, this vulnerability poses a serious risk of unauthorized access to sensitive knowledge bases. Attackers can remotely bypass authentication without credentials, leading to potential data theft, unauthorized data modification, and loss of data integrity. Organizations relying on Trilium for storing proprietary, confidential, or regulated information could face data breaches, intellectual property theft, or compliance violations under GDPR. The compromise of knowledge bases may also facilitate further lateral movement or social engineering attacks if sensitive operational or personnel information is exposed. Although availability is not directly impacted, the loss of confidentiality and integrity could disrupt business processes and damage organizational reputation. The lack of known exploits in the wild currently reduces immediate risk but does not eliminate the threat, especially as attackers may develop exploits given the public disclosure.

European organizations should immediately upgrade all Trilium Notes instances to version 0.101.0 or later to remediate this vulnerability. If upgrading is not immediately feasible, organizations should restrict network access to the sync authentication endpoint by implementing firewall rules or VPN access controls to limit exposure to trusted users only. Monitoring network traffic for unusual timing patterns or repeated authentication attempts may help detect exploitation attempts. Additionally, organizations should audit existing knowledge bases for unauthorized access or modifications and consider rotating any related credentials or secrets. Employing application-layer protections such as rate limiting and anomaly detection on authentication endpoints can further reduce risk. Finally, educating users about the importance of timely software updates and maintaining an inventory of deployed software versions will help prevent exploitation of similar vulnerabilities in the future.