CVE-2026-39846: SiYuan: Remote Code Execution in the Electron desktop client via stored XSS in synced table captions

Should you act?

Critical, preconditions apply

Severe if exploited, but exploitation needs conditions that may not apply to you. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.7%, percentile 51: FIRST’s model estimates a 0.7% chance of exploitation activity in the next 30 days, higher than 51% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Needs an account (low (any account)). Exposure depends on who can log in.
• Only applies if your dependency tree includes github.com/siyuan-note/siyuan/kernel (Go) < 0.0.0-20260407035653-2f416e5253f1, fixed in 0.0.0-20260407035653-2f416e5253f1. Check your lockfile, including transitive dependencies.

What it is

SiYuan is a personal knowledge management system. Prior to 3.6.4, a malicious note synced to another user can trigger remote code execution in the SiYuan Electron desktop client. The root cause is that table caption content is stored without safe escaping and later unescaped into rendered HTML, creating a stored XSS sink. Because the desktop renderer runs with nodeIntegration enabled and contextIsolation disabled, attacker-controlled JavaScript executes with access to Node.js APIs. In practice, an attacker can import a crafted note into a synced workspace, wait for the victim to sync, and achieve code execution when the victim opens the note. This vulnerability is fixed in 3.6.4.

From the GitHub advisory

Summary A malicious note synced to another user can trigger remote code execution in the SiYuan Electron desktop client. The root cause is that table caption content is stored without safe escaping and later unescaped into rendered HTML, creating a stored XSS sink. Because the desktop renderer runs with nodeIntegration enabled and contextIsolation disabled, attacker-controlled JavaScript executes with access to Node.js APIs. In practice, an attacker can import a crafted note into a synced workspace, wait for the victim to sync, and achieve code execution when the victim opens the note.

Details The vulnerability exists in the table caption handling path. When a table block is parsed, the caption attribute is saved into the node's IAL properties without proper HTML escaping. Later, during rendering, that value is read back, passed through HTML unescaping, and written directly into the output DOM. This turns an attacker-controlled caption into active HTML inside the rendered note.

I confirmed that a crafted table caption containing encoded HTML such as &lt;img src=x onerror=...&gt; is rendered as a live DOM element instead of inert text. This makes the issue a stored XSS. I also confirmed that the most practical delivery path is not Markdown import, but a crafted .sy.zip note imported into a synced workspace. Once synced to another desktop client, opening the note executes the payload automatically.

In the Electron desktop client, this XSS results in code execution rather than browser-only script execution. The renderer is configured with nodeIntegration: true and contextIsolation: false, so JavaScript running in the note context can call Node.js APIs directly. A payload such as require('childprocess').exec('calc') executes successfully, demonstrating code execution on the victim machine in the context of the logged-in user.

PoC

Weakness type: CWE-79, CWE-94.

Product: github.com/siyuan-note/siyuan/kernel (Go) · Assigned by: GitHub_M · Published: 2026-04-07

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: low (any account)
• User interaction: required (a user must click/open something)
• Scope: changed (can affect other components)

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable no, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.65% probability of exploitation activity in the next 30 days; percentile 51.

Timeline

• 2026-04-07 — CVE record published by GitHub_M
• 2026-04-08 — CVE record last updated
• 2026-04-08 — GitHub-reviewed advisory GHSA-phhp-9rm9-6gr2 published (critical)

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-phhp-9rm9-6gr2 github.com
2. CVE.org record CVE-2026-39846 cve.org
3. NVD entry CVE-2026-39846 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com

Critical Go advisories · Today’s Security Digest