# CVE-2026-100640: SiYuan before v3.8.4 Clipboard Data Disclosure via IPC

> Attackers controlling remote renderer content can access local clipboard data, including MathML, Office, and WPS bytes, during user-mediated paste operations.

- **Severity:** High 8.6 (`CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 26 Sep 2026
- **Updated:** 27 Oct 2026
- **Also known as:** GHSA-5r83-25qj-w6vh, GHSA-mjmm-hgmc-m7qf

## What is CVE-2026-100640?

CVE-2026-100640 is a high-severity vulnerability in siyuan-note siyuan, published on 26 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

SiYuan before v3.8.4 contains an authorization omission in the siyuan-get IPC handler that allows remote-kernel renderers to access native clipboard formats by invoking clipboardReadMathML, clipboardReadOffice, and clipboardReadWPS commands with matching plaintext. Attackers controlling remote renderer content can obtain MathML formulas, Office bytes, and WPS bytes from local clipboard during user-mediated paste operations.

Weakness: CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor)

## Which versions are affected by CVE-2026-100640?


## How do I fix CVE-2026-100640?

No fix has been published for CVE-2026-100640 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-100640 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-100640 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-100640 and fix it if it is affected.

What it is: CVE-2026-100640 is a high-severity vulnerability in siyuan-note siyuan, published on 26 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-100640 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-2026-100640/ (Markdown: https://insights.sbomify.com/CVE-2026-100640/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-100640
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-100640
- OSV: https://osv.dev/vulnerability/CVE-2026-100640

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-100640/
Summaries are generated and may contain mistakes; the official description above is the record.