CVE-2026-55551

ZAC is an open-source, workflow-based Common Ground component for Dutch municipal case management. Prior to 5.2.0, by-id read endpoints in src/main/kotlin/nl/info/zac/app/zaak/ZaakRestService.kt omit assertPolicy(policyService.readZaakRechten(zaak).lezen) authorization. RequestAuthorizationFilter and hasAnyApplicationRole require only an application role on any zaaktype, not the target case's type, while zaak-rechten.rego enforces the actual zaaktype_allowed boundary only when invoked. An authenticated low-privileged municipal user who knows a case or decision UUID can use GET /rest/zaken/besluit/zaakUuid/{uuid} (listBesluitenForZaakUUID) to read decisions including types, dates, and free-text toelichting; GET /rest/zaken/besluit/{uuid}/historie (listBesluitHistorie) to read audit old/new values; and GET /rest/zaken/{uuid}/process-diagram (downloadProcessDiagram) to read BPMN workflow state across unauthorized zaaktypes. The advisory also identifies zaak/{uuid}/afzender (listAfzendersVoorZaak) as exposing zaaktype mailbox configuration without a policy check. The search/_zoek path is correctly authorization-filtered and is not part of this by-id read cluster. This issue is fixed in version 5.2.0.