Trilium Notes versions before 0.103.0 improperly neutralize input during web page generation, specifically in the handling of the #iconClass label value returned by getNoteIcon(). This value is inserted without HTML attribute encoding into class attributes in apps/client/src/widgets/quick_search.ts and apps/client/src/services/note_autocomplete.ts. This flaw enables stored cross-site scripting (XSS) payloads to execute automatically when a victim opens a new tab or uses the Ctrl+J shortcut. Because the application is built on Electron with nodeIntegration enabled and contextIsolation disabled, the XSS can escalate to executing operating system commands under the victim's context. The vulnerability is tracked as CVE-2026-45733 and has a CVSS 3.1 score of 8.3 (high severity). The vulnerability is fixed in Trilium version 0.103.0.

Successful exploitation allows an attacker to execute arbitrary code on the victim's machine by leveraging stored XSS in the application interface. This can lead to full compromise of the victim's operating system environment due to Electron's insecure default configuration in affected versions. The impact includes high confidentiality, integrity, and availability loss as indicated by the CVSS vector.

Upgrade Trilium Notes to version 0.103.0 or later, where this vulnerability is fixed. No other mitigation or temporary workaround is indicated by the vendor advisory. Users should ensure they are not running affected versions.