EUVD-2026-76692
GHSA-6h3c-r723-7fx3
Severity by source
AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
Any authenticated citizen (PR:L) reaches the network GraphQL mutation with no user interaction to read and overwrite another user's task data (C:H/I:H), with no availability impact (A:N).
Primary rating from Vendor (https://github.com/nl-portal/nl-portal-backend-libraries).
CVSS VectorVendor: https://github.com/nl-portal/nl-portal-backend-libraries
Lifecycle Timeline
1Blast Radius
ecosystem impact- 2 maven packages depend on nl.nl-portal:taak (2 direct, 0 indirect)
Ecosystem-wide dependent count for version 1.5.0.
DescriptionCVE.org
Impact
In versions from 1.5.0 up to and including 3.0.0, any authenticated portal user could complete and tamper with another user's open task by submitting it on their behalf. The task submission endpoint accepted a task ID and a payload, but it never checked whether the task actually belonged to the user making the call.
An attacker who held a valid login (a normal burger OAuth token) and who knew or guessed another user's task ID could:
- Mark someone else's task as completed.
- Overwrite the data submitted with that task - the
verzonden_data- with arbitrary input of their choosing. - Receive the full task back in the GraphQL response, including the form data that the legitimate owner had already entered. This leaks personal data belonging to the original user.
Functionally this means a malicious authenticated user could submit and alter forms in any other user's name, while at the same time reading what that user had previously filled in. Both the integrity of submitted data and the confidentiality of form contents are affected.
The vulnerable code was introduced together with the Taak V2 implementation (commit bb1c1ecf, 2024-06-04) and first shipped in the 1.5.x release line. Earlier 1.x releases did not contain this resolver.
Patches
Upgrade to 3.0.1 or later.
Fix commit: 8e699add - "Add auth check for task submission".
Workarounds
Until the upgrade is applied, block the submitTaakV2 GraphQL mutation at the API gateway, or restrict the /graphql endpoint to trusted networks.
Technical details
The resolver nl.nlportal.zgw.taak.service.TaakService.submitTaakV2(id, submission, authentication) fetched the task object by UUID and immediately transitioned it to the AFGEROND state, writing record.data.portaalformulier.verzondenData from caller-supplied input. No check verified that the task's identificatie matched the authenticated burger.
The fix adds a call to a new isAuthorizedForTaak(authentication, objectsApiTask) before the status change. The check compares identificatie.type and identificatie.value against the authenticated principal and validates the task's eigenaar for bedrijf machtigingen.
Credits
Discovered during the nl-portal-backend-libraries penetration testing engagement (phase 1, May 2026). Vendor attribution to be added before publication.
AnalysisAI
Insecure Direct Object Reference in NL Portal's Taak V2 module (nl.nl-portal:taak) versions 1.5.0 through 3.0.0 lets any authenticated portal user holding a valid 'burger' OAuth token complete and tamper with another user's task by supplying its task ID. Because the submitTaakV2 GraphQL mutation never verified task ownership, an attacker can overwrite another user's submitted form data (verzondenData) and read that user's previously entered personal data returned in the GraphQL response, breaking both integrity and confidentiality. No public exploit is identified at time of analysis, but the flaw is trivially exploitable by any logged-in user against a horizontally-adjacent task object.
Technical ContextAI
NL Portal is a set of Dutch government 'Common Ground' backend libraries used to build citizen-facing municipal portals, exposing functionality over GraphQL and authenticating citizens via 'burger' OAuth tokens. The defect lives in nl.nlportal.zgw.taak.service.TaakService.submitTaakV2(id, submission, authentication), which fetched a task object by UUID and immediately transitioned it to the AFGEROND (completed) state while writing record.data.portaalformulier.verzondenData from caller-supplied input. This is a textbook CWE-639 (Authorization Bypass Through User-Controlled Key / IDOR): the server trusts a client-supplied task UUID as an access key without verifying that the requesting principal owns the object. The affected artifact is the Maven package pkg:maven/nl.nl-portal:taak, and the vulnerable resolver was introduced with the Taak V2 implementation (commit bb1c1ecf, 2024-06-04), first shipping in the 1.5.x line.
RemediationAI
Vendor-released patch: 3.0.1 - upgrade the nl.nl-portal:taak dependency to 3.0.1 or later, which adds the isAuthorizedForTaak(authentication, objectsApiTask) ownership check (fix commit 8e699add) validating identificatie.type and identificatie.value against the authenticated principal and the task eigenaar for bedrijf machtigingen. If you cannot upgrade immediately, block the submitTaakV2 GraphQL mutation at the API gateway (this disables legitimate Taak V2 form submission through that mutation until patched), or restrict the /graphql endpoint to trusted networks (which breaks public citizen access and is only viable for internal or administrative deployments). Details and the fix are documented in advisory GHSA-6h3c-r723-7fx3 (https://github.com/nl-portal/nl-portal-backend-libraries/security/advisories/GHSA-6h3c-r723-7fx3).
Same technique Authentication Bypass
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External POC / Exploit Code
Leaving vuln.today