CVE-2026-50551: SiYuan: Stored XSS to RCE via Unsanitized Attribute View Asset Cell Content

SiYuan v3.6.5 and earlier versions contain a stored cross-site scripting (XSS) vulnerability in the Attribute View (database) asset cell renderer that escalates to remote code execution (RCE) in the Electron desktop client. This is a neighbor-bug of CVE-2026-44588: the fix for -44588 used escapeAriaLabel() (double-escapes <), but the AV asset renderers were left using the weaker escapeAttr() (escapes only quotes) or no escaping at all.

## Vulnerability Details

The Electron renderer is configured with nodeIntegration: true and contextIsolation: false (app/electron/main.js:307), allowing any JavaScript executing in the renderer to directly access Node.js APIs including require('childprocess').

Two XSS sinks exist.

### Sink 1 (Direct Stored XSS - triggers on page load)

app/src/protyle/render/av/cell.ts:1008:

text += <span class="b3-chip avcelltext--url ariaLabel" aria-label="${escapeAttr(item.content)}" data-name="${escapeAttr(item.name)}" data-url="${escapeAttr(item.content)}">${item.name || item.content}</span>;

The >${item.name || item.content}</span> portion is raw user input with zero escaping.

app/src/protyle/render/av/blockAttr.ts:93 (even worse - completely unescaped):

html += <img loading="lazy" class="avcellassetimg ariaLabel" aria-label="${item.content}" src="${getCompressURL(item.content)}">;

Rendered via action.ts:860: cellElement.innerHTML = renderCell(...) results in immediate XSS on page load.

### Sink 2 (Hover-triggered XSS via aria-label round-trip)

- Same lines emit aria-label="${escapeAttr(item.content)}" on .ariaLabel elements. - escapeAttr() (util/escape.ts:14) escapes only " and ' — NOT < or >. - popover.ts:33 global mouseover handler reads aria-label via getAttribute (which attribute-decodes entities). - Line 144: showTooltip(decodeURIComponent(tip), ...) then tooltip.ts:41: messageElement.innerHTML = message results in XSS on hover.

### Source

- app/src/protyle/render/av/asset.ts:405: addAssetLink() reads user input from a free-form <textarea> with no sanitization. - Kernel stores MAsset.Content raw (kernel/av/value.go:53), no server-side sanitization.

## Attack Vector

1. Attacker creates a malicious note containing an Attribute View (database). 2. Attacker adds an asset cell with link content: <img src=x onerror=require('childprocess').exec('calc')> 3. Victim opens the note for immediate RCE (Sink 1), or hovers over the cell for RCE (Sink 2). 4. In a sync/collaboration scenario, the malicious note propagates to all users.

## Proof of Concept

Payload (Direct XSS) — in an AV asset cell link field, enter:

<img src=x onerror=alert(document.domain)>

For RCE in Electron desktop:

<img src=x onerror=require('childprocess').exec('calc')>

### Steps to Reproduce

1. Open SiYuan desktop app (v3.6.5). 2. Create a new document. 3. Insert an Attribute View (database): / then select "Table". 4. Add a column of type "Asset". 5. Click the asset cell, then "Add Link". 6. In the "Link" textarea, paste: <img src=x onerror=alert(1)> 7. Leave "Title" empty or fill with benign text. 8. Click outside the dialog to save. 9. Observe: Alert fires immediately (Sink 1). Hovering over the cell also triggers (Sink 2).

## Impact

- Remote Code Execution on victim's system via malicious note sync/import. - Data exfiltration: attacker can read all notes, access filesystem, steal credentials. - Persistence: malicious payload stored in .sy files, executes on every open.

## Suggested Fix

1. Replace escapeAttr() with escapeAriaLabel() for all aria-label attributes in AV cell renderers. 2. Escape item.name and item.content with escapeHtml() before concatenating into element text content.

Affected files: app/src/protyle/render/av/cell.ts, app/src/protyle/render/av/blockAttr.ts, app/src/protyle/render/av/asset.ts.

## Additional Context

This vulnerability is a neighbor-bug of CVE-2026-44588. The fix for -44588 correctly used escapeAriaLabel() (which double-escapes < to survive the attribute -> getAttribute -> innerHTML round-trip), but the AV asset cell renderers were left using the weaker escapeAttr() or no escaping. This is part of a pattern of incomplete fixes in SiYuan (see also CVE-2026-33066, CVE-2026-29183). The long-term fix should set ElectroncontextIsolation: true and nodeIntegration: false.

## Report Reporter (GitHub: Yunkaiwjs).

— GitHub