CVE-2026-100639 SiYuan before v3.8.4 Cross-Site Scripting via Kramdown IAL
An attacker can achieve remote code execution by tricking a victim into pasting malicious Markdown that triggers XSS in the Electron desktop application.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-100639?
CVE-2026-100639 is a high-severity cross-site scripting vulnerability in siyuan-note siyuan, published on 26 Sep 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
SiYuan v3.8.3 fails to HTML-escape the data-subtype attribute when generating gutter-button markup (app/src/protyle/gutter/button.ts, assigned via innerHTML in app/src/protyle/gutter/index.ts) from content pasted as plain-text Markdown containing a Kramdown inline attribute list (IAL). Because the shared Lute renderer parses Kramdown IAL from text/plain input, an attacker-supplied Markdown snippet using entity-encoded quotes in data-subtype breaks out of the attribute value when the gutter markup is re-parsed by the browser, injecting additional attributes such as autofocus and onfocus. If a victim pastes the crafted Markdown and the affected gutter control receives focus, the injected handler executes; in the Electron desktop application, where the main BrowserWindow enables Node integration and disables context isolation, this results in JavaScript execution with renderer Node.js privileges (remote code execution). Fixed in v3.8.4.
Weakness: CWE-79
Which versions are affected by CVE-2026-100639?
How do I fix CVE-2026-100639?
No fix has been published for CVE-2026-100639 yet. Limit exposure of the affected software until one is available.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-100639 being exploited?
There is no known exploitation of CVE-2026-100639 in the wild and no public exploit code.
Sources
Also known as GHSA-2cmm-9x9j-rvff, GHSA-r9x8-34vf-7m8q.