{"id":"CVE-2026-63097","summary":"Dendrite 0.13.8 syncapi /context Endpoint Post-Leave State Exposure","details":"Dendrite through 0.13.8 contains an improper access control vulnerability in the syncapi /context endpoint (syncapi/routing/context.go) that allows authenticated local users to access post-leave room state events by exploiting a flawed membership check that evaluates only the RoomExists field while ignoring IsInRoom, HasBeenInRoom, and Membership fields. Attackers who have left a room can call the rooms context API endpoint for a previously permitted event and receive unfiltered current room state that the /messages and /sync endpoints correctly withhold.","modified":"2026-07-19T03:47:18.368776373Z","published":"2026-07-17T15:32:45.411Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63097.json","cna_assigner":"VulnCheck","cwe_ids":["CWE-863"]},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63097.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-63097"},{"type":"ADVISORY","url":"https://www.vulncheck.com/advisories/dendrite-syncapi-context-endpoint-post-leave-state-exposure"},{"type":"PACKAGE","url":"https://github.com/matrix-org/dendrite"},{"type":"EVIDENCE","url":"https://github.com/geo-chen/oss/blob/main/dendrite.md#finding-3-context-returns-current-room-state-to-non-members-and-left-users-history-visibility-bypass"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/matrix-org/dendrite","events":[{"introduced":"0"},{"last_affected":"763c79f1421200c3fd74401fd68298bc00ecefbc"}],"database_specific":{"source":"AFFECTED_FIELD","extracted_events":[{"introduced":"0"},{"last_affected":"0.13.8"}]}}],"versions":["v0.13.8","helm-dendrite-0.14.2","v0.13.7","helm-dendrite-0.14.1","helm-dendrite-0.14.0","helm-dendrite-0.13.8","v0.13.6","helm-dendrite-0.13.7","v0.13.5","helm-dendrite-0.13.6","v0.13.4","helm-dendrite-0.13.5","v0.13.3","helm-dendrite-0.13.4","helm-dendrite-0.13.3","helm-dendrite-0.13.2","v0.13.2","helm-dendrite-0.13.1","v0.13.1","v0.13.0","helm-dendrite-0.13.0","helm-dendrite-0.12.4","helm-dendrite-0.12.3","helm-dendrite-0.12.2","helm-dendrite-0.12.1","v0.12.0","helm-dendrite-0.12.0","helm-dendrite-0.11.2","v0.11.1","helm-dendrite-0.11.1","v0.11.0","helm-dendrite-0.11.0","helm-dendrite-0.10.9","v0.10.9","helm-dendrite-0.10.8","v0.10.8","v0.10.7","v0.10.6","v0.10.5","v0.10.4","v0.10.3","v0.10.2","v0.10.1","v0.10.0","v0.9.9","v0.9.8","v0.9.7","v0.9.6","v0.9.5","v0.9.4","v0.9.3","v0.9.2","v0.9.1","v0.9.0","v0.8.9","v0.8.8","v0.8.7","v0.8.6","v0.8.5","v0.8.4","v0.8.3","v0.8.3rc1","v0.8.2","v0.8.1","v0.8.0","v0.7.0","v0.6.5","v0.6.4","v0.6.3","v0.6.2","v0.6.1","v0.6.0","v0.6","v0.5.1","v0.5.0","v0.5.0rc1","v0.4.1","v0.4.0","v0.3.11","v0.3.10","v0.3.9","v0.3.8","v0.3.7","v0.3.6","v0.3.5","v0.3.4","v0.3.3","v0.3.2","v0.3.1","v0.3.0","v0.2.1","v0.2.0","v0.1.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-63097.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N"}]}