CVE-2026-105784 in Joplin
Summary
by MITRE • 10/06/2026
Joplin is an open source note-taking and to-do application that organises notes and lists into notebooks. Prior to 3.7.13, selecting a note containing a jsoncanvas fence causes the whiteboard text and file-node components in packages/app-desktop/gui/NoteEditor/NoteBody/WhiteboardEditor/nodes/TextNode.tsx and packages/app-desktop/gui/NoteEditor/NoteBody/WhiteboardEditor/nodes/FileNode.tsx to render card content with the full Markdown renderer. The components insert the resulting HTML into the main application document through dangerouslySetInnerHTML. A malicious note can inject style elements and remote CSS imports that modify trusted application chrome, signal when the note is opened, and potentially disclose exposed attribute values. Content Security Policy blocks inline script execution, so the supported impact is CSS injection and UI redressing rather than code execution. This issue is fixed in version 3.7.13.
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Analysis
by VulDB Data Team • 10/06/2026
The vulnerability identified in Joplin versions prior to 3.7.13 represents a significant security flaw rooted in improper neutralization of special elements within HTML output, commonly categorized under CWE-80: Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS). The application utilizes the jsoncanvas fence syntax for notes containing whiteboard content, which triggers specific rendering components located at packages/app-desktop/gui/NoteEditor/NoteBody/WhiteboardEditor/nodes/TextNode.tsx and FileNode.tsx. These components are responsible for displaying text and file nodes within the whiteboard interface. However, they implement a critical security anti-pattern by inserting rendered HTML directly into the main application document using dangerouslySetInnerHTML without adequate sanitization or context-aware escaping of potentially malicious content embedded in Markdown sources.
When an attacker crafts a note containing a jsoncanvas fence with injected style elements and remote CSS imports, the vulnerable components process this input through the full Markdown renderer. The resulting HTML is then placed directly into the DOM via the unsafe method mentioned above. This allows for CSS injection attacks where external stylesheets can be loaded from malicious servers controlled by an adversary. Because Joplin operates as a desktop application with webview-based interfaces, it inherits many of the risks associated with browser-side vulnerabilities. The ability to inject remote CSS imports enables the attacker to override existing style rules and manipulate the visual presentation of trusted application chrome elements that are normally protected or distinct from user content areas.
The operational impact of this vulnerability extends beyond simple cosmetic changes. By leveraging injected styles, an adversary can perform UI redressing attacks, a technique aligned with MITRE ATT&CK tactic T1078: Valid Accounts and sub-technique T1548: Abuse Elevation Control Mechanism in the context of social engineering or interface manipulation. The attacker can modify trusted application chrome to mimic legitimate dialogs, buttons, or input fields, thereby deceiving users into performing unintended actions such as entering credentials or confirming malicious operations. Furthermore, the injection mechanism allows for signaling when a note is opened by triggering specific CSS animations or network requests that report back to an external server. This capability facilitates user activity tracking and profiling without explicit consent, violating principles of privacy and data protection.
Additionally, the vulnerability potentially exposes exposed attribute values within the application interface. By manipulating DOM elements through injected styles, attackers may access properties or attributes that were not intended for public exposure, leading to information disclosure. Although Content Security Policy (CSP) directives in Joplin effectively block inline script execution, preventing direct JavaScript code injection and arbitrary command execution, this mitigation does not protect against CSS-based attacks. The CSP restricts the scope of impact primarily to visual manipulation and tracking rather than full remote code execution, but it fails to mitigate risks related to user deception and data leakage through style-based side channels.
To remediate this issue, users must upgrade Joplin to version 3.7.13 or later, where the rendering logic has been corrected to prevent unsafe HTML insertion. For developers maintaining similar applications, the primary mitigation involves avoiding dangerouslySetInnerHTML for untrusted content and instead using robust sanitization libraries such as DOMPurify that are configured with strict allowlists for allowed tags and attributes. Implementing a Content Security Policy that restricts inline styles and limits external resource loading can further reduce the attack surface. Additionally, adopting secure coding practices that emphasize context-aware output encoding ensures that special characters in user input are properly escaped before being rendered into HTML structures, thereby neutralizing potential injection vectors at their source.