CVE-2026-100635 HIGH

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

Vendor Siyuan-Note
Product siyuan
Weakness CWE-319 · Cleartext transmission
Published September 26, 2026
Last update October 27, 2026

CVSS base score

8.2/10
Attack vector Network
Attack complexity Low
Privileges required None
User interaction None
Confidentiality —
Integrity —

CVSS 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

What the vulnerability does

01Description

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.

Key dates

02Disclosure timeline

September 26, 2026 CVE published
October 27, 2026 Record updated