CVE-2026-28803: Maykinmedia Open Forms

Medium severity, CVSS 6.5. EPSS: 0.4% chance of exploitation in the next 30 days.

Open Forms allows users create and publish smart forms. Prior to 3.3.13 and 3.4.5, to be able to cosign, the cosigner receives an e-mail with instructions or a deep-link to start the cosign flow. The submission reference is communicated so that the user can retrieve the submission to be cosigned. Attackers can guess a code or modify the received code to look up arbitrary submissions, after logging in (with DigiD/eHerkenning/... depending on form configuration). This vulnerability is fixed in 3.3.13 and 3.4.5.

Affected products

• Maykinmedia Open Forms: before 3.3.13 (fixed in 3.3.13); from 3.4.0, before 3.4.5 (fixed in 3.4.5)

Published 2026-03-11. Last modified 2026-06-17.