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CVE-2026-85584 – Denial of Service (Memory Exhaustion) – SiYuan Note before v3.8.2

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Summary

CVE-2026-85584 is a denial-of-service vulnerability in SiYuan Note’s publish-service Basic Auth throttle mechanism. Versions before v3.8.2 store failed authentication attempts keyed by attacker-controlled usernames without any capacity limit or eviction policy, allowing unauthenticated attackers to exhaust server memory. The issue carries a CVSS score of 8.7 and can degrade or disable service availability for affected instances.

Technical details

  • Root cause: the publish-service Basic Auth throttle stores failed login attempts in a map keyed by a combination of remote address and username, with no global maximum entry count, periodic eviction, or TTL-based cleanup for unrelated keys.
  • Trigger condition: an attacker repeatedly submits authentication attempts using unique, invalid usernames; each failed attempt creates a new persistent map entry.
  • Attack vector: network-based, requires no authentication and no user interaction.
  • Impact: unbounded memory growth and increased synchronization overhead, leading to resource exhaustion and degraded or unavailable service (availability impact only; no confidentiality or integrity impact).

Affected software

  • SiYuan Note (b3log/siyuan-note) versions prior to v3.8.2 (all versions using the original throttle-map design, including v3.8.1 and earlier)

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 Base 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 Note to v3.8.2 or later, which introduces a bounded eviction policy for the authentication throttle.
  • If patching is not immediately possible: restrict network exposure of the publish-service authentication endpoint (e.g., place it behind a VPN, IP allow-list, or reverse proxy with rate limiting) to reduce the ability of unauthenticated remote attackers to send high volumes of distinct-username login attempts.

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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