# CVE-2026-100634: SiYuan before v3.8.4 Missing Authorization via siyuan-send-windows

> An attacker can remotely lock unrelated local workspace windows in SiYuan via IPC, causing a denial of service.

- **Severity:** Medium 5.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:L/SC:N/SI:N/SA:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 26 Sep 2026
- **Updated:** 8 Oct 2026
- **Also known as:** GHSA-w745-gjg3-r76m, GHSA-wxp7-xpq8-8xpm

## What is CVE-2026-100634?

CVE-2026-100634 is a medium-severity missing authorization vulnerability in siyuan-note siyuan, published on 26 Sep 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

SiYuan before v3.8.4 does not validate the sender or restrict recipients in the 'siyuan-send-windows' IPC handler of the Electron main process (app/electron/main.js). The handler ignores event.sender and forwards any received payload to every BrowserWindow returned by BrowserWindow.getAllWindows(), including windows belonging to other opened workspaces. A renderer connected to an attacker-controlled remote kernel can therefore send {cmd: "lockscreenByMode"} and have it delivered across the workspace boundary; a sibling workspace window whose lockScreenMode is set to 1 invokes lockScreen(). Repeated messages allow the remote workspace to repeatedly lock unrelated local workspace windows, causing a limited denial of service. No confidentiality, integrity, or code-execution impact was observed.

Weakness: CWE-862 (Missing Authorization)

## Which versions are affected by CVE-2026-100634?


## How do I fix CVE-2026-100634?

No fix has been published for CVE-2026-100634 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-100634 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-100634 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-100634 and fix it if it is affected.

What it is: CVE-2026-100634 is a medium-severity missing authorization vulnerability in siyuan-note siyuan, published on 26 Sep 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-100634 exists.

Affected product: siyuan-note siyuan. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-100634/ (Markdown: https://insights.sbomify.com/CVE-2026-100634/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-100634
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-100634
- OSV: https://osv.dev/vulnerability/CVE-2026-100634

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-100634/
Summaries are generated and may contain mistakes; the official description above is the record.