CVE-2026-100639

SiYuan before v3.8.4 Cross-Site Scripting via Kramdown IAL

HIGH
8.8
CVSS Score
Published: September 26, 2026 at 01:23 PM UTC
Updated: September 28, 2026 at 07:16 PM UTC
2 products affected across 2 vendorsSiyuanSiyuan

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Severity
HIGH8.8
Exploit prediction
EPSS 0.5%
SSVC
No known exploit

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

v < 3.8.4
Affected range stops below 3.8.4, so it looks safe — our inference, not a vendor statement
v < 3.8.4
Vendor states this is fixed in 3.8.4 (unaffected)

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

SSVC — Action Prioritization

SSVCNo known exploitNot automatableTotal impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

8.8HIGHVulnCheck
Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
REQUIRED
Scope
UNCHANGED
Confidentiality
HIGH
Integrity
HIGH
Availability
HIGH
Vector?

Quick Info

StatusDEFERRED
CWE
CWE-79

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