CVE-2026-63097

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.

CVSS v3 4.3 MEDIUM

4.3^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 2.8 / Impact : 1.4

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required LOW

User Interaction NONE

Confidentiality Impact LOW

Integrity Impact NONE

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
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
https://www.vulncheck.com/advisories/dendrite-syncapi-context-endpoint-post-leave-state-exposure

Configurations

No configuration.

History

24 Oct 2026, 20:10

Type	Values Removed	Values Added
Summary		(es) Dendrite hasta la versión 0.13.8 contiene una vulnerabilidad de control de acceso inadecuado en el endpoint /context de syncapi (syncapi/routing/context.go) que permite a usuarios locales autenticados acceder a eventos de estado de sala posteriores a la salida explotando una verificación de membresía defectuosa que evalúa solo el campo RoomExists mientras ignora los campos IsInRoom, HasBeenInRoom y Membership. Atacantes que han abandonado una sala pueden llamar al endpoint API de contexto de salas para un evento previamente permitido y recibir el estado actual de la sala sin filtrar que los endpoints /messages y /sync retienen correctamente.

Information

Published : 2026-07-17 16:17

Updated : 2026-10-24 20:10

NVD link : CVE-2026-63097

Mitre link : CVE-2026-63097

CVE.ORG link : CVE-2026-63097

JSON object : View

Products Affected

No product.

CWE

CWE-863

Incorrect Authorization

{"id": "CVE-2026-63097", "cveTags": [{"tags": ["unsupported-when-assigned"], "sourceIdentifier": "disclosure@vulncheck.com"}], "metrics": {"ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-63097", "role": "CISA Coordinator", "options": [{"exploitation": "poc"}, {"automatable": "no"}, {"technicalImpact": "partial"}], "version": "2.0.3", "timestamp": "2026-07-23T19:18:43.951534Z"}}], "cvssMetricV31": [{"type": "Secondary", "source": "disclosure@vulncheck.com", "cvssData": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 4.3, "attackVector": "NETWORK", "baseSeverity": "MEDIUM", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N", "integrityImpact": "NONE", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "NONE", "privilegesRequired": "LOW", "confidentialityImpact": "LOW"}, "impactScore": 1.4, "exploitabilityScore": 2.8}], "cvssMetricV40": [{"type": "Secondary", "source": "disclosure@vulncheck.com", "cvssData": {"Safety": "NOT_DEFINED", "version": "4.0", "Recovery": "NOT_DEFINED", "baseScore": 5.3, "Automatable": "NOT_DEFINED", "attackVector": "NETWORK", "baseSeverity": "MEDIUM", "valueDensity": "NOT_DEFINED", "vectorString": "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X", "exploitMaturity": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED", "userInteraction": "NONE", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "LOW", "subIntegrityImpact": "NONE", "vulnIntegrityImpact": "NONE", "integrityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "vulnAvailabilityImpact": "NONE", "availabilityRequirement": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "subConfidentialityImpact": "NONE", "vulnConfidentialityImpact": "LOW", "confidentialityRequirement": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED"}}]}, "affected": [{"source": "disclosure@vulncheck.com", "affectedData": [{"repo": "https://github.com/matrix-org/dendrite", "vendor": "matrix-org", "product": "dendrite", "versions": [{"status": "affected", "version": "0", "versionType": "semver", "lessThanOrEqual": "0.13.8"}], "defaultStatus": "affected"}]}], "published": "2026-07-17T16:17:16.783", "references": [{"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", "source": "disclosure@vulncheck.com"}, {"url": "https://www.vulncheck.com/advisories/dendrite-syncapi-context-endpoint-post-leave-state-exposure", "source": "disclosure@vulncheck.com"}], "vulnStatus": "Deferred", "weaknesses": [{"type": "Secondary", "source": "disclosure@vulncheck.com", "description": [{"lang": "en", "value": "CWE-863"}]}], "descriptions": [{"lang": "en", "value": "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."}, {"lang": "es", "value": "Dendrite hasta la versi\u00f3n 0.13.8 contiene una vulnerabilidad de control de acceso inadecuado en el endpoint /context de syncapi (syncapi/routing/context.go) que permite a usuarios locales autenticados acceder a eventos de estado de sala posteriores a la salida explotando una verificaci\u00f3n de membres\u00eda defectuosa que eval\u00faa solo el campo RoomExists mientras ignora los campos IsInRoom, HasBeenInRoom y Membership. Atacantes que han abandonado una sala pueden llamar al endpoint API de contexto de salas para un evento previamente permitido y recibir el estado actual de la sala sin filtrar que los endpoints /messages y /sync retienen correctamente."}], "lastModified": "2026-10-24T20:10:00.137", "sourceIdentifier": "disclosure@vulncheck.com"}