# CVE-2026-100639: SiYuan gutter attribute injection and remote code execution

Source: https://junglewise.ai/threats/cve-2026-100639-siyuan-v3-8-3-fails-to-html-escape-the-data-subtype-attribute  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-26. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-100639 · Severity: high · CVSS 8.8 · Published 2026-09-26

SiYuan is a note-taking and knowledge management application available as a web and desktop application. Versions up to v3.8.3 fail to properly escape HTML attributes when processing pasted Markdown content, allowing an attacker to inject malicious code. When a victim pastes crafted Markdown and interacts with the application, the injected code executes with full application privileges; on the Windows/macOS/Linux desktop versions, this results in remote code execution with access to the underlying system. The fix is available in v3.8.4.

Technologies: [SiYuan Note SiYuan](https://junglewise.ai/threats/technologies/siyuan-note-siyuan). Vendors: [SiYuan Note](https://junglewise.ai/threats/vendors/siyuan-note).

## Quick answers

**Is CVE-2026-100639 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-100639 being exploited in the wild.

**How severe is CVE-2026-100639?** High severity, with a CVSS score of 8.8, published 26 September 2026.

**Which products and versions are affected?** SiYuan Note SiYuan 3.8.3 and earlier.

**Is there a fix for CVE-2026-100639?** A patch was published on 2026-09-10: Fixed in v3.8.4 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-100639 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-100639?** Check whether you run SiYuan Note SiYuan at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A Cross-Site Scripting vulnerability occurs in the gutter-button generator (button.ts) which fails to HTML-escape the data-subtype attribute before inserting it via innerHTML. The attack vector requires a victim to paste attacker-controlled Markdown with Kramdown IAL containing entity-encoded quotes that break attribute parsing, injecting autofocus and onfocus handlers. The vulnerability chain involves the Lute Markdown renderer parsing IAL from plain-text input, followed by unescaped interpolation into the gutter button template and re-parsing by the DOM. In the Electron desktop application with Node integration enabled and context isolation disabled, focus events on the injected gutter control execute JavaScript with renderer Node.js privileges.

## Affected products

- siyuan-note SiYuan 3.8.3 and earlier

## Timeline

- 2026-09-26: disclosed: CVE-2026-100639 published
- 2026-09-10: patched: Fixed in v3.8.4

## References

- [https://github.com/siyuan-note/siyuan/security/advisories/GHSA-2cmm-9x9j-rvff](https://github.com/siyuan-note/siyuan/security/advisories/GHSA-2cmm-9x9j-rvff)
- [https://www.vulncheck.com/advisories/siyuan-before-3.8.4-cross-site-scripting-via-kramdown-ial](https://www.vulncheck.com/advisories/siyuan-before-3.8.4-cross-site-scripting-via-kramdown-ial)

## Related threats

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- [SiYuan stored cross-site scripting in KaTeX math blocks](https://junglewise.ai/threats/cve-2026-116169-siyuan-from-2-10-0-before-3-8-7-contains-a-stored-cross-site)
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