CVE-2026-55551: Access Control Flaw (CVSS 6.5)

Description

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.

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CVSS v3.1 Score

6.5

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

EPSS — Exploit Prediction

0.0026

Probability of exploitation

0.17%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-285 CWE-285

CWE-639 CWE-639

References

Other References

https://github.com/infonl/dimpact-zaakafhandelcomponent/commit/7b90586be658cec9fa5c98c0838636237f40931f https://github.com/infonl/dimpact-zaakafhandelcomponent/commit/d050f247301a1bcfb867015725a693c540a06f5a https://github.com/infonl/dimpact-zaakafhandelcomponent/pull/6225 https://github.com/infonl/dimpact-zaakafhandelcomponent/pull/6229 https://github.com/infonl/dimpact-zaakafhandelcomponent/releases/tag/v5.2.0 https://github.com/infonl/dimpact-zaakafhandelcomponent/security/advisories/GHSA-cv9m-35q4-cxfm

Frequently Asked Questions

What is 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. It has a CVSS v3.1 base score of 6.5 (MEDIUM).

How severe is CVE-2026-55551? +

CVE-2026-55551 has a CVSS v3.1 score of 6.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0026, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-55551? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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