Dendrite 0.13.8 syncapi /context Endpoint Post-Leave State Exposure
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.
- Products
- Not specified
- Affected versions
- Not specified
- Fixed versions
- Not specified
- CVEs
- CVE-2026-63097
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 4 Nov 2026, 11:33 UTC · Revision 1
Source evidence
Dendrite 0.13.8 syncapi /context Endpoint Post-Leave State Exposure
core-osv · Original sourcePublished 17 Jul 2026, 15:32 UTC
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.
osv:CVE-2026-63097
Complete source record
{
"id": "dd9fac793fec5bd6c006be6b8f53bc4e9ea13a898a295bf5fca797f327bfc166",
"url": "https://osv.dev/vulnerability/CVE-2026-63097",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "Dendrite 0.13.8 syncapi /context Endpoint Post-Leave State Exposure",
"summary": "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.",
"evidence": "osv:CVE-2026-63097",
"products": [],
"severity": "medium",
"structured": {
"id": "CVE-2026-63097",
"aliases": [
"CVE-2026-63097"
],
"metrics": [
{
"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"
}
],
"affected": [
{
"ranges": [
{
"repo": "https://github.com/matrix-org/dendrite",
"type": "GIT",
"events": [
{
"introduced": "0"
},
{
"last_affected": "763c79f1421200c3fd74401fd68298bc00ecefbc"
}
],
"database_specific": {
"extracted_events": [
{
"range": [
{
"introduced": "0"
},
{
"last_affected": "0.13.8"
}
],
"source": "AFFECTED_FIELD",
"strategy": "StandardRange"
}
]
}
}
],
"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"
}
}
],
"modified": "2026-10-28T02:30:34.567174321Z",
"provider": "osv",
"references": [
"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63097.json",
"https://nvd.nist.gov/vuln/detail/CVE-2026-63097",
"https://www.vulncheck.com/advisories/dendrite-syncapi-context-endpoint-post-leave-state-exposure",
"https://github.com/matrix-org/dendrite",
"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"
],
"provider_metadata": {
"cwe_ids": [
"CWE-863"
],
"cna_assigner": "VulnCheck",
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63097.json"
}
},
"related_cves": [
{
"value": "CVE-2026-63097",
"evidence": "/id"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 502030,
"published_at": "2026-07-17T15:32:45.411+00:00"
}