Description
SiYuan before 3.8.9 contains a nil pointer dereference vulnerability in privateCacheMiddleware that allows authenticated attackers to crash the kernel by reading nonexistent MCP resources. Attackers with a valid API token can send a resources/read request in an initialized MCP session, causing a panic that terminates the kernel process and interrupts service.
Published: 2026-11-06
Score: 6.9 Medium
EPSS: n/a
KEV: No
Impact: Denial of Service
Action: Immediate Patch
AI Analysis

Impact

A nil pointer dereference in the privateCacheMiddleware of SiYuan allows an authenticated attacker to crash the kernel process by requesting a non‑existent MCP resource. The resulting panic terminates the kernel and interrupts service, effectively causing a denial of service. The weakness is classified as CWE-476.

Affected Systems

SiYuan versions prior to 3.8.9 released by Siyuan Note are affected. Any deployment of the open‑source note‑taking application that includes an MCP session and step allowing a resources/read call can be vulnerable if the version is <3.8.9.

Risk and Exploitability

The CVSS score of 6.9 indicates a moderate severity level. The EPSS score is not available, and the vulnerability is not listed in CISA’s KEV catalog, suggesting that widespread exploitation is unlikely but still plausible. Exploitation requires a valid API token and network access to the MCP session; once achieved, the attacker can cause a service outage by sending a resources/read request for a missing resource.

Generated by OpenCVE AI on November 6, 2026 at 16:43 UTC.

Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

  • Upgrade SiYuan to version 3.8.9 or later to eliminate the null‑pointer dereference
  • Revoke or rotate all existing API tokens that could be used to invoke MCP sessions until the patch is applied
  • Disable the MCP resources/read endpoint or block incoming requests to that API path via firewall or API gateway as a temporary defense

Generated by OpenCVE AI on November 6, 2026 at 16:43 UTC.

Tracking

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Advisories

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History

Fri, 06 Nov 2026 17:15:00 +0000

Type Values Removed Values Added
First Time appeared Siyuan
Siyuan siyuan
Vendors & Products Siyuan
Siyuan siyuan

Fri, 06 Nov 2026 15:15:00 +0000

Type Values Removed Values Added
Description SiYuan before 3.8.9 contains a nil pointer dereference vulnerability in privateCacheMiddleware that allows authenticated attackers to crash the kernel by reading nonexistent MCP resources. Attackers with a valid API token can send a resources/read request in an initialized MCP session, causing a panic that terminates the kernel process and interrupts service.
Title SiYuan before 3.8.9 Nil Pointer Dereference DoS via MCP resources/read
First Time appeared B3log
B3log siyuan
Weaknesses CWE-476
CPEs cpe:2.3:a:b3log:siyuan:*:*:*:*:*:*:*:*
Vendors & Products B3log
B3log siyuan
References
Metrics cvssV3_1

{'score': 4.9, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H'}

cvssV4_0

{'score': 6.9, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N'}

Subscriptions

B3log Siyuan
Siyuan Siyuan
cve-icon MITRE

Status: PUBLISHED

Assigner: VulnCheck

Published:

Updated: 2026-11-06T15:00:52.853Z

Reserved: 2026-11-06T00:44:37.659Z

Link: CVE-2026-123492

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Deferred

Published: 2026-11-06T15:17:18.830

Modified: 2026-11-06T15:17:18.963

Link: CVE-2026-123492

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-11-06T17:00:09Z

Weaknesses