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CVE-2026-85585 – Unbounded Memory Consumption / Denial of Service – SiYuan Note (before v3.8.2)

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Summary

CVE-2026-85585 is an uncontrolled resource consumption (CWE-400) vulnerability in SiYuan Note, an open-source note-taking application. A flaw in the request-concurrency middleware fails to evict mutex entries created for each unique request path, allowing an unauthenticated remote attacker to exhaust server memory and degrade availability. The issue affects all SiYuan versions prior to 3.8.2 and carries a HIGH severity rating.

Technical details

  • Root cause: The request-concurrency middleware creates and retains a mutex entry for every unique request path it processes, with no eviction or expiry mechanism.
  • Trigger condition: An attacker sends a large number of requests using varied/unique paths to the SiYuan HTTP interface, causing the mutex table to grow unbounded.
  • Attack vector: Network-based; no authentication and no user interaction are required to exploit.
  • Impact: Continuous growth in process memory and synchronization overhead, leading to degraded performance or denial of service on the affected instance.

Affected software

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

Severity

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

Mitigation and recommended actions

  • Immediate: Upgrade SiYuan to version 3.8.2 or later, which fixes the mutex-eviction flaw.
  • If patching is not immediately possible: Restrict network exposure of the SiYuan HTTP interface (e.g., place it behind a firewall, VPN, or reverse proxy with rate limiting) to reduce the ability of unauthenticated remote parties to send high volumes of varied requests, and monitor server memory usage for abnormal growth.

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 response body: exitSiYuan, b3log.org/siyuan

References

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