{"id":"CVE-2026-100646","title":"SiYuan is a self-hosted personal knowledge management system","summary":"SiYuan is a self-hosted personal knowledge management system. In versions up to and including 3.8.3, the kernel's authentication guards (CheckAuth in kernel/model/session.go and IsSessionOriginAllowed in kernel/util/net.go) fail open whe…","severity":"high","cvss":8.1,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N","cwe":["CWE-346"],"vendor":"siyuan-note","product":"siyuan","affected":["siyuan < 3.8.4"],"published":"2026-09-26","updated":"2026-09-30","sourceUpdated":"2026-09-30T15:21:53.333","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-100646","references":[{"url":"https://github.com/siyuan-note/siyuan/security/advisories/GHSA-2w6q-wgc8-q743","label":"disclosure@vulncheck.com"},{"url":"https://www.vulncheck.com/advisories/siyuan-before-3.8.4-authentication-bypass-via-missing-origin-header","label":"disclosure@vulncheck.com"},{"url":"https://github.com/siyuan-note/siyuan/security/advisories/GHSA-2w6q-wgc8-q743","label":"134c704f-9b21-4f2e-91b3-4a467353bcc0"}],"tags":["nvd","cve.org","exploit-available"],"epss":0.0024,"epssPercentile":0.14962,"exploitAvailable":true,"ssvc":{"exploitation":"poc","automatable":"no","technicalImpact":"total","timestamp":"2026-09-30T14:46:38.827782Z"},"ingestedAt":"2026-09-26T13:33:20.921Z","slug":"CVE-2026-100646","body":"## Overview\n\nSiYuan is a self-hosted personal knowledge management system. In versions up to and including 3.8.3, the kernel's authentication guards (CheckAuth in kernel/model/session.go and IsSessionOriginAllowed in kernel/util/net.go) fail open when the HTTP Origin header is absent, on the incorrect assumption that any browser-initiated cross-site request carries an Origin. Because browsers omit Origin on cross-site top-level GET navigations and no-cors GET subresource loads — and the session cookie is SameSite=Lax — a single cross-site GET issued from any attacker-controlled web page is granted RoleAdministrator, both on default installations with no access-authorization code and on password-protected instances with a live session. Combined with content-type sniffing on the /api/network/proxy endpoint, which allows attacker-controlled HTML to be served under SiYuan's own origin, this permits an unauthenticated remote attacker to execute arbitrary script in the SiYuan origin (http://127.0.0.1:6806), invoke administrator APIs, and exfiltrate the persistent kernel API token. This issue is fixed in version 3.8.4.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"midnight","depthScore":57,"depthScoreParts":{"impact":44.6,"likelihood":0,"exploitation":12,"ransomware":0},"changes":[{"seq":213723,"id":"CVE-2026-100646","ts":1790780950700,"field":"exploit_available","old":"false","new":"true"}]}