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.

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)

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.

Affected products

Siyuan-note Siyuan

Weakness classification (CWE)

CWE-639 — Authorization Bypass Through User-Controlled Key

References

disclosure@vulncheck.com (vendor-advisory)
disclosure@vulncheck.com (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.