CVE-2026-87809

Status: DeferredHigh (7.1)—

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.

CVSS

Version: 4.0
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/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
Base score: 7.1

Exploitation probability (EPSS)

Probability of exploitation in the next 30 days: 0.35%
Percentile among all scored CVEs: 27
Score date: 10/4/2026

EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).

🎯 ATT&CK techniques

How this vulnerability is exploited and what the attacker gains, in MITRE ATT&CK terms.

ExploitationT1210 Exploitation of Remote Serviceslateral movement75 %
Primary impactT1005 Data from Local Systemcollection80 %
Secondary impactT1550.001 Application Access Tokenlateral movement60 %

AV:N, PR:L sin UI:R: acceso remoto autenticado (T1210). CWE-639 (autorización insuficiente) permite lectura de datos privados vía endpoints expuestos (/api/export/preview, /api/lute/copyStdMarkdown) sin filtrado de acceso (T1005). PR:L implica reutilización de credenciales válidas (T1550.001).

Inferred by our analysis agent from the official description, CVSS vector and CWE, and checked by a supervisor. May contain errors.

🛡️ ATT&CK mitigations that cover these techniques

Application Developer Guidance Vulnerability Scanning Threat Intelligence Program Restrict Web-Based Content Privileged Account Management Network Segmentation

Affected technologies (1)

⚠ AI-inferred from the description — NVD hasn't analyzed this CVE yet, these aren't verified CPEs.

B3log — Siyuan^AI

CWEs

CWE-639

References

Raw JSON (NVD)

Show

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          "options": [
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              "automatable": "no"
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              "technicalImpact": "partial"
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          "version": "2.0.3",
          "timestamp": "2026-09-18T17:08:58.264762Z"
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    "cvssMetricV40": [
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          "valueDensity": "NOT_DEFINED",
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          "integrityRequirement": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
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          "vulnAvailabilityImpact": "NONE",
          "availabilityRequirement": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
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          "modifiedAttackRequirements": "NOT_DEFINED",
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          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "vulnerabilityResponseEffort": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED"
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  "affected": [
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      "affectedData": [
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          "vendor": "siyuan-note",
          "product": "siyuan",
          "versions": [
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              "version": "0",
              "lessThan": "3.8.2",
              "versionType": "semver"
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  "published": "2026-09-09T12:17:15.650",
  "references": [
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      "source": "disclosure@vulncheck.com"
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    {
      "url": "https://www.vulncheck.com/advisories/siyuan-before-3.8.2-information-disclosure-via-export-preview",
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    {
      "lang": "en",
      "value": "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."
    }
  ],
  "lastModified": "2026-09-18T18:17:33.600",
  "sourceIdentifier": "disclosure@vulncheck.com"
}