CVE-2026-100640: SiYuan Information Disclosure Vulnerability

CVE-2026-100640 Overview

CVE-2026-100640 is an information disclosure vulnerability in SiYuan, a self-hosted personal knowledge management application. Versions prior to v3.8.4 contain an authorization omission in the siyuan-get inter-process communication (IPC) handler. The flaw allows remote-kernel renderers to access native clipboard formats by invoking clipboardReadMathML, clipboardReadOffice, and clipboardReadWPS commands with matching plaintext. Attackers who control remote renderer content can exfiltrate MathML formulas, Microsoft Office bytes, and WPS Office bytes from the local clipboard during user-mediated paste operations. The weakness is tracked as CWE-200: Exposure of Sensitive Information to an Unauthorized Actor.

Critical Impact
Attackers can harvest sensitive clipboard contents including proprietary Office documents, WPS files, and MathML formulas from local users without triggering standard clipboard access warnings.

Affected Products

SiYuan Note versions prior to v3.8.4
SiYuan desktop clients using the siyuan-get IPC handler
Installations loading remote-kernel renderer content

Discovery Timeline

2026-09-26 - CVE-2026-100640 published to NVD
2026-09-28 - Last updated in NVD database

Technical Details for CVE-2026-100640

Vulnerability Analysis

SiYuan exposes an IPC bridge named siyuan-get that renderer processes use to request privileged operations from the main process. The handler fails to verify whether the invoking renderer is permitted to read native clipboard formats beyond plaintext. When a renderer calls clipboardReadMathML, clipboardReadOffice, or clipboardReadWPS with a matching plaintext argument, the handler returns the corresponding native clipboard payload. This authorization omission widens the trust boundary between remote-kernel renderers and the host clipboard.

Root Cause

The root cause is missing authorization enforcement in the siyuan-get IPC handler. The handler treats all renderer-origin calls as trusted and uses a plaintext-match check rather than an origin or capability check. Remote-kernel renderers that load untrusted content inherit the same clipboard-reading capabilities intended only for local, trusted UI code.

Attack Vector

Exploitation requires an attacker to control the content rendered inside a remote-kernel renderer context, typically through malicious notes, documents, or embedded web resources opened in SiYuan. When a user performs a paste action, the attacker-controlled renderer invokes the vulnerable IPC commands and retrieves clipboard payloads in MathML, Office, or WPS formats. The attack is user-mediated through the paste operation but does not require additional privileges or authentication. See the GitHub Security Advisory GHSA-mjmm-hgmc-m7qf and the VulnCheck Advisory for SiYuan for additional technical context.

Detection Methods for CVE-2026-100640

Indicators of Compromise

Unexpected invocations of clipboardReadMathML, clipboardReadOffice, or clipboardReadWPS originating from remote-kernel renderer processes.
SiYuan log entries showing siyuan-get IPC calls immediately following user paste events into untrusted documents.
Outbound network traffic from SiYuan processes containing serialized Office or WPS binary payloads shortly after paste actions.

Detection Strategies

Audit SiYuan application logs for high-frequency siyuan-get IPC calls targeting the three clipboard-read commands.
Monitor endpoint telemetry for SiYuan child processes making outbound HTTPS requests immediately after clipboard interaction.
Inventory installed SiYuan versions across endpoints and flag any build earlier than v3.8.4.

Monitoring Recommendations

Enable process and child-process telemetry on hosts running SiYuan to capture renderer-to-main IPC behavior.
Alert on SiYuan processes transmitting binary payloads to non-corporate destinations shortly after document rendering.
Correlate clipboard-access events with user paste actions to identify unexpected format reads.

How to Mitigate CVE-2026-100640

Immediate Actions Required

Upgrade SiYuan to v3.8.4 or later on all desktop endpoints.
Restrict SiYuan to loading only trusted, locally authored content until patched.
Avoid copying sensitive Office, WPS, or MathML data to the clipboard while SiYuan is running an unpatched build.

Patch Information

The vendor fixed the vulnerability in SiYuan v3.8.4 by enforcing authorization checks in the siyuan-get IPC handler. Patch details are documented in the GitHub Security Advisory GHSA-mjmm-hgmc-m7qf.

Workarounds

Block SiYuan from loading remote renderer content by disabling third-party plugins and remote notebook sources.
Operate SiYuan under a least-privileged user account that does not have access to sensitive documents.
Use application allowlisting to prevent unpatched SiYuan builds from executing on managed endpoints.

bash

# Verify installed SiYuan version and remove outdated builds
siyuan --version
# If output is below v3.8.4, uninstall and install the patched release