Auth bypass in Siyuan-Note Siyuan
CVE-2026-87809
Siyuan before v3.8.2 fails to apply publish-access filtering to embedded blocks before rendering in the /api/export/preview and /api/lute/copyStdMarkdown endpoints. Attackers with reader access can retrieve the full rendered content of private, hidden, or publish-disabled blocks by accessing public documents containing embed queries that select those blocks.
Vulnerability class: IDOR (Insecure Direct Object Reference)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N.
EPSS exploit prediction
EPSS: 0.004 (27.9th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 28th percentile — 27.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: 0.000
Affected products
Weakness classification (CWE)
References
- github.com/siyuan-note/siyuan/security/advisories/GHSA-8wx4-fvqw-f5f8 (vendor-advisory)
- www.vulncheck.com/advisories/siyuan-before-3.8.2-information-disclosure-via-exp… (third-party-advisory)
Frequently asked questions
- What is CVE-2026-87809?
- CVE-2026-87809 is a medium-severity vulnerability in Siyuan-Note Siyuan, classified under Authorization Bypass Through User-Controlled Key. CVSS score: 6.5/10. Published 2026-09-09.
- How severe is CVE-2026-87809?
- Medium severity. CVSS v3 base score is 6.5 out of 10.