---
id: CVE-2026-100646
title: SiYuan is a self-hosted personal knowledge management system
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 whe…
severity: high
cvss: 8.1
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N'
cwe:
  - CWE-346
vendor: siyuan-note
product: siyuan
affected:
  - siyuan < 3.8.4
published: '2026-09-26'
updated: '2026-09-26'
sourceUpdated: '2026-09-26T14:16:47.047'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-100646'
references:
  - url: >-
      https://github.com/siyuan-note/siyuan/security/advisories/GHSA-2w6q-wgc8-q743
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/siyuan-before-3.8.4-authentication-bypass-via-missing-origin-header
    label: disclosure@vulncheck.com
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-26T13:33:20.921Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.