# CVE-2026-66394: SiYuan before v3.7.3 Stored and Reflected XSS via SVG Sanitizer Bypass

> Authenticated attackers can execute arbitrary scripts in SiYuan by bypassing SVG sanitization, potentially compromising user sessions and data.

- **Severity:** Critical 9.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 27 Jul 2026
- **Updated:** 8 Oct 2026
- **Also known as:** GHSA-5p6m-3744-5c8g, GHSA-99rq-75j6-5j9f, GO-2026-6364

## What is CVE-2026-66394?

CVE-2026-66394 is a critical cross-site scripting vulnerability in siyuan-note siyuan, published on 27 Jul 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official description

SiYuan before v3.7.3 contains stored and reflected cross-site scripting vulnerabilities in SVG sanitization that allows authenticated attackers to execute scripts by bypassing the HTML parser-based cleaner. Attackers can hide script tags within desc, style, or noscript elements which the HTML parser treats as raw text but browsers interpret as executable SVG content when served as image/svg+xml, enabling script execution in the application origin.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2026-66394?

3 open source packages ship an affected version, including github.com/siyuan-note/siyuan/kernel.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/siyuan-note/siyuan/kernel` | Go | All versions | 0.0.0-20260714095344-f08dee71ba8e |
| `github.com/siyuan-note/siyuan/kernel` | Go | All versions | 0.0.0-20260714095344-f08dee71ba8e |
| `github.com/siyuan-note/siyuan/kernel` | Go | All versions | 0.0.0-20260714095344-f08dee71ba8e |

## How do I fix CVE-2026-66394?

Upgrade github.com/siyuan-note/siyuan/kernel to 0.0.0-20260714095344-f08dee71ba8e or later.

## Is CVE-2026-66394 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-66394 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-66394 and fix it if it is affected.

What it is: CVE-2026-66394 is a critical cross-site scripting vulnerability in siyuan-note siyuan, published on 27 Jul 2026. Any signed-in user can exploit it over the network, 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-2026-66394 exists.

Affected packages and fixed versions:
- github.com/siyuan-note/siyuan/kernel (Go): affected all versions; fixed in 0.0.0-20260714095344-f08dee71ba8e
- github.com/siyuan-note/siyuan/kernel (Go): affected all versions; fixed in 0.0.0-20260714095344-f08dee71ba8e
- github.com/siyuan-note/siyuan/kernel (Go): affected all versions; fixed in 0.0.0-20260714095344-f08dee71ba8e

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-2026-66394/ (Markdown: https://insights.sbomify.com/CVE-2026-66394/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-66394
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-66394
- OSV: https://osv.dev/vulnerability/CVE-2026-66394

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-66394/
Summaries are generated and may contain mistakes; the official description above is the record.