What is CVE-2026-59809?

CVE-2026-59809 is a medium-severity vulnerability in Siyuan-Note Siyuan, classified under Insertion of Sensitive Information into Sent Data. CVSS score: 4.9/10. Published 2026-08-22.

How severe is CVE-2026-59809?

Medium severity. CVSS v3 base score is 4.9 out of 10.

Vulnerability in Siyuan-Note Siyuan

CVE-2026-59809

SiYuan before v3.8.0 interpolates secret placeholders into the destination URL parameter of the http_request MCP tool, allowing attackers to exfiltrate stored secrets. An MCP client can craft a request with an attacker-controlled URL containing secret placeholders to send plaintext secret values to any public host without confirmation.

CVSS v3 metric

CVSS v3 base score 4.9 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N.

Affected products

Siyuan-note Siyuan

Weakness classification (CWE)

CWE-201 — Insertion of Sensitive Information into Sent Data

References

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

Frequently asked questions

What is CVE-2026-59809?: CVE-2026-59809 is a medium-severity vulnerability in Siyuan-Note Siyuan, classified under Insertion of Sensitive Information into Sent Data. CVSS score: 4.9/10. Published 2026-08-22.
How severe is CVE-2026-59809?: Medium severity. CVSS v3 base score is 4.9 out of 10.