{"schema":"threatline.record/2","record":{"id":"CVE-2026-100646","aliases":["GHSA-2w6q-wgc8-q743"],"summary":"SiYuan before v3.8.4 Authentication Bypass via Missing Origin Header","details":"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 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.","categories":["Unclassified"],"product":"siyuan","vendor":"siyuan-note","ecosystem":null,"affected_ranges":[{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-100646","source_modified_at":"2026-09-30T14:47:14.800Z","fetched_at":"2026-10-23T18:52:38.922436Z","product":"siyuan","vendor":"siyuan-note","versions":[{"version":"0","status":"affected","versionType":"semver","lessThan":"3.8.4"},{"version":"3.8.4","status":"unaffected","versionType":"semver"}],"defaultStatus":"unaffected"}],"fixed_versions":[{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-100646","source_modified_at":"2026-09-30T14:47:14.800Z","fetched_at":"2026-10-23T18:52:38.922436Z","package":{"name":"siyuan","ecosystem":null},"version":"3.8.4","basis":"first unaffected version stated in the CVE record"}],"cvss":8.6,"severity":"High","kev":{"listed":false},"epss":{"probability":0.00194,"percentile":0.08584,"score_date":"2026-10-23"},"published_at":"2026-09-26T13:23:17.483Z","modified_at":"2026-09-30T14:47:14.800Z","provenance":[{"source":"CVE List","url":"https://www.cve.org/CVERecord?id=CVE-2026-100646","fetched_at":"2026-10-23T18:52:38.922436Z","source_modified_at":"2026-09-30T14:47:14.800Z"},{"source":"EPSS","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-100646","fetched_at":"2026-10-23T18:42:43.628194Z","source_modified_at":"2026-10-23"}],"sources":["CVE List","EPSS"],"references":[{"source":"CVE List","url":"https://github.com/siyuan-note/siyuan/security/advisories/GHSA-2w6q-wgc8-q743","tags":["exploit"]},{"source":"CVE List","url":"https://www.vulncheck.com/advisories/siyuan-before-3.8.4-authentication-bypass-via-missing-origin-header","tags":["third-party-advisory"]}],"locations":[],"motoko_assessment":{"status":"requires_architecture_review","automatic_remediation":false},"cve_state":"PUBLISHED","cvss_source":"CVE List","ssvc":{"exploitation":"poc","automatable":"no","technical_impact":"total","assessed_at":"2026-09-30T14:46:38.827782Z"},"classification":{"method":"product-first software-layer rules","rules_version":"2.1","matched_on":null,"confidence":"unknown","reviewed":false},"change_timestamp":"2026-09-30T14:47:14.800Z","content_hash":"ae25b51364e565aa7dc0624147891df21e266f8a9230230d76ba6d5be3214f37"}}