{"schema_version":"1","data":[{"id":4420,"advisory_id":"91d20039-a475-4075-8bef-80fdce9b5255","revision":1,"source_id":"core-cve","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-100646","source_published_at":"2026-09-26T13:23:17.483+00:00","published_at":"2026-10-24T21:51:21.707091+00:00","extraction_method":"structured","technologies":["core-cve","siyuan"],"cve_ids":["CVE-2026-100646"],"event_types":["advisory"],"payload":{"kind":"advisory","title":"SiYuan before v3.8.4 Authentication Bypass via Missing Origin Header","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 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.","evidence":"cve:CVE-2026-100646","products":[{"name":{"value":"siyuan","evidence":"/containers/cna/affected/0/product"},"prerequisites":[],"fixed_versions":[],"affected_versions":[]}],"severity":"high","structured":{"id":"CVE-2026-100646","aliases":["CVE-2026-100646"],"metrics":[{"format":"CVSS","cvssV4_0":{"version":"4.0","baseScore":8.6,"attackVector":"NETWORK","baseSeverity":"HIGH","vectorString":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N","userInteraction":"PASSIVE","attackComplexity":"LOW","attackRequirements":"NONE","privilegesRequired":"NONE","subIntegrityImpact":"NONE","vulnIntegrityImpact":"HIGH","subAvailabilityImpact":"NONE","vulnAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","vulnConfidentialityImpact":"HIGH"}},{"format":"CVSS","cvssV3_1":{"scope":"UNCHANGED","version":"3.1","baseScore":8.1,"attackVector":"NETWORK","baseSeverity":"HIGH","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N","integrityImpact":"HIGH","userInteraction":"REQUIRED","attackComplexity":"LOW","availabilityImpact":"NONE","privilegesRequired":"NONE","confidentialityImpact":"HIGH"}}],"affected":[{"vendor":"siyuan-note","product":"siyuan","versions":[{"status":"affected","version":"0","lessThan":"3.8.4","versionType":"semver"},{"status":"unaffected","version":"3.8.4","versionType":"semver"}],"packageURL":"pkg:golang/github.com/siyuan-note/siyuan","defaultStatus":"unaffected"}],"modified":"2026-09-30T14:47:14.800Z","provider":"cve","references":["https://github.com/siyuan-note/siyuan/security/advisories/GHSA-2w6q-wgc8-q743","https://www.vulncheck.com/advisories/siyuan-before-3.8.4-authentication-bypass-via-missing-origin-header"],"provider_metadata":{"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-100646","role":"CISA Coordinator","options":[{"Exploitation":"poc"},{"Automatable":"no"},{"Technical Impact":"total"}],"version":"2.0.3","timestamp":"2026-09-30T14:46:38.827782Z"}}}],"references":[{"url":"https://github.com/siyuan-note/siyuan/security/advisories/GHSA-2w6q-wgc8-q743","tags":["exploit"]}],"providerMetadata":{"orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","shortName":"CISA-ADP","dateUpdated":"2026-09-30T14:47:14.800Z"}}],"cna":{"orgId":"83251b91-4cc7-4094-a5c7-464a1b83ea10","shortName":"VulnCheck","dateUpdated":"2026-09-26T13:23:17.483Z"}}},"related_cves":[{"value":"CVE-2026-100646","evidence":"/cveMetadata/cveId"}],"security_relevant":true,"severity_evidence":"/containers/cna/metrics"}}],"next_after":4420,"next_before":4420}