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CVE-2026-87807 – Authenticated SQL Injection – SiYuan Note before v3.8.2

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Summary

CVE-2026-87807 is an authenticated SQL injection vulnerability in SiYuan Note, a self-hosted note-taking application. The flaw exists in the fullTextSearchBlock API endpoint’s method=1 parameter and allows an authenticated attacker to inject UNION SELECT statements, reading the entire blocks table and bypassing publish-access controls. All SiYuan versions prior to 3.8.2 are affected; the issue was fixed in 3.8.2.

Technical details

  • Root cause: Improper neutralization of special elements used in an SQL command (CWE-89) within the fullTextSearchBlock endpoint when handling the method=1 search parameter.
  • Trigger conditions: An authenticated user (or a user with access to a published/shared SiYuan instance) submits a crafted method=1 search query containing a UNION SELECT payload.
  • Attack vector: Network — no local access or physical interaction required; exploitation occurs over the exposed HTTP API.
  • Impact: Full read access to the blocks table, exposing document content and other sensitive data stored in the notebook database, and bypassing intended publish-access restrictions.

Affected software

  • SiYuan Note (b3log/siyuan-note) — all versions prior to 3.8.2

Severity

  • CVSS v3.1 Base Score: 7.5 (High) — Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
  • Also scored under CVSS v4.0 at 8.7 (High) — Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate: Upgrade SiYuan Note to version 3.8.2 or later, which contains the fix for this issue.
  • If patching is not immediately possible: Restrict network access to SiYuan instances (avoid direct internet exposure), disable or restrict public/anonymous access to publish/share features, and monitor logs for anomalous full-text search queries containing SQL syntax such as UNION SELECT.

How IONIX identifies potentially affected assets

IONIX matches the following signals against data already collected when it crawled the asset; identifying the technology sends no request beyond that crawl.

  • Page title: Access Authorization - SiYuan, 思源笔记
  • Raw HTTP response body: exitSiYuan, b3log.org/siyuan

References

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