Vulnerability in Maykinmedia Open Forms
CVE-2026-28803
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N.
EPSS exploit prediction
EPSS: 0.003 (24.9th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 25th percentile — 24.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.003 · change: +0.001
Affected products
- Maykinmedia Open Forms
- Open-Formulieren Open-Forms — versions >= 3.4.0-alpha.0, < 3.4.5, < 3.3.13
Weakness classification (CWE)
References
- github.com/open-formulieren/open-forms/security/advisories/GHSA-2g49-rfm6-5qj5 (Mitigation, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-28803?
- CVE-2026-28803 is a medium-severity vulnerability in Maykinmedia Open Forms, classified under Improper Access Control. CVSS score: 6.5/10. Published 2026-03-11.
- How severe is CVE-2026-28803?
- Medium severity. CVSS v3 base score is 6.5 out of 10.