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CVE-2026-100646: Product identification pending

Severity

8.6 (HIGH)

Affected versions

up to and including 3

Fixed version

3.8.4.

Patch status

Patched

Published

2026-09-26T14:16:46.900

Modified

2026-09-26T14:16:47.047

Why it matters

This matters because the issue affects identity or token handling. Successful exploitation could allow unauthorized authentication, client manipulation, or access to protected services.

Recommended admin actions

• Review and patch based on exposure, asset criticality, and business impact.
• Treat internet-facing systems as higher priority.
• Review logs for suspicious activity related to the affected application or component.

Technical summary

SiYuan is a self-hosted personal knowledge management system. In versions up to and including 3.8.3, the kernel's authentication guards (CheckAuth in kernel/model/session.go and IsSessionOriginAllowed in kernel/util/net.go) fail open when the HTTP Origin header is absent, on the incorrect assumption that any browser-initiated cross-site request carries an Origin. Because browsers omit Origin on cross-site top-level GET navigations and no-cors GET subresource loads — and the session cookie is SameSite=Lax — a single cross-site GET issued from any attacker-controlled web page is granted RoleAdministrator, both on default installations with no access-authorization code and on password-protected instances with a live session. Combined with content-type sniffing on the /api/network/proxy endpoint, which allows attacker-controlled HTML to be served under SiYuan's own origin, this permits an unauthenticated remote attacker to execute arbitrary script in the SiYuan origin (http://127.0.0.1:6806), invoke administrator APIs, and exfiltrate the persistent kernel API token. This issue is fixed in version 3.8.4.

View the official NVD record for CVE-2026-100646

CVE data is sourced from NVD/CNA records and optional enrichment. Validate against the vendor advisory before taking production action.