What’s Vulnerable › Vulnerabilities

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

• Severity: medium (CVSS 5.9 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-26 · updated 2026-10-27
• Weakness: CWE-319

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.

Affected products

• siyuan-note siyuan: before 3.8.4 — fixed in 3.8.4

How to fix

Upgrade to a fixed version: siyuan-note siyuan 3.8.4. Check the vendor advisory for mitigations.

References

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

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