Vulnerability in Siyuan-Note Siyuan
CVE-2026-100646
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 8.1 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
Weakness classification (CWE)
References
- github.com/siyuan-note/siyuan/security/advisories/GHSA-2w6q-wgc8-q743 (vendor-advisory)
- www.vulncheck.com/advisories/siyuan-before-3.8.4-authentication-bypass-via-miss… (third-party-advisory)
Frequently asked questions
- What is CVE-2026-100646?
- CVE-2026-100646 is a high-severity vulnerability in Siyuan-Note Siyuan, classified under Origin Validation Error. CVSS score: 8.1/10. Published 2026-09-26.
- How severe is CVE-2026-100646?
- High severity. CVSS v3 base score is 8.1 out of 10.