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SiYuan CVE-2026-59809

| EUVDEUVD-2026-64267 MEDIUM
Insertion of Sensitive Information Into Sent Data (CWE-201)
2026-08-22 VulnCheck GHSA-27jw-6xjf-hgxj
Information Disclosure Siyuan
6.9
CVSS 4.0 · Vendor: VulnCheck
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Vendor (VulnCheck) PRIMARY
6.9 MEDIUM
CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
vuln.today AI
4.9 MEDIUM

MCP client access required (PR:H); network-reachable once authenticated (AV:N); only confidentiality impacted via plaintext secret exfiltration, no integrity or availability effect.

3.1 AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N
4.0 AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Primary rating from Vendor (VulnCheck).

CVSS VectorVendor: VulnCheck

Attack Vector
Network
Attack Complexity
Low
Privileges Required
High
User Interaction
None
Scope
X

Lifecycle Timeline

2
Patch available
Aug 22, 2026 - 13:16 EUVD
Analysis Generated
Aug 22, 2026 - 13:12 vuln.today

DescriptionCVE.org

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.

AnalysisAI

Secret exfiltration via URL parameter interpolation in SiYuan's http_request MCP tool affects all versions before v3.8.0. An MCP client with elevated access can embed secret placeholder references directly in the destination URL of an http_request tool call, causing SiYuan to resolve and transmit stored plaintext secrets to any attacker-controlled host without user confirmation. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

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Execution
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Vulnerability AssessmentAI

Exploitation Exploitation requires that the attacker holds MCP client-level access to the target SiYuan instance (CVSS PR:H) - this is not available to arbitrary remote unauthenticated users. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 4.0 score of 6.9 with vector AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:N/VA:N reflects a meaningful but access-gated risk. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario Full exploit scenario with step-by-step reproduction available after sign-in.
Remediation Upgrade SiYuan to v3.8.0 or later, which eliminates secret placeholder interpolation in the http_request MCP tool's URL parameter; the vendor advisory at https://github.com/siyuan-note/siyuan/security/advisories/GHSA-853m-gvvm-6rvx confirms this as the primary fix. … Detailed patch versions, workarounds, and compensating controls in full report.
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CVE-2026-59809 vulnerability details – vuln.today
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