Is CVE-2026-28803 in the CISA KEV catalog?

No. CVE-2026-28803 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-28803?

CVE-2026-28803 has a CVSS v3 base score of 6.5 (MEDIUM).

What is the EPSS score for CVE-2026-28803?

CVE-2026-28803 has an EPSS score of 0.20% (10th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-28803?

Upgrade open forms to 3.4.5 or later.

CVE & CISA-KEV Catalog

CVE-2026-28803

MEDIUM

6.5

CVSS v3

NVD

Description

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.

CWE-284Improper Access Control

How to fix

Remediation Available

open formsNVD

Affected:>= 3.4.0, < 3.4.5Fixed in:3.4.5CVE-2026-28803derived from NVD

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredLow

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityHigh

IntegrityNone

AvailabilityNone

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

Exploit Intelligence

0.20%probability of exploitation in 30 days

10thpercentile

Low risk: more likely to be exploited than 10% of all known CVEs.

References

Vendor Advisory1

github.com

Related Vulnerabilities

Other CWE-284 (Improper Access Control) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2023-27350	Critical	9.8	100%	KEV + Ransom	Fix
CVE-2019-1653	High	7.5	100%	KEV	-
CVE-2023-23752	Medium	5.3	100%	KEV	Fix
CVE-2023-29298	High	7.5	100%	KEV	-
CVE-2023-38205	High	7.5	100%	KEV	-
CVE-2024-27348	Critical	9.8	99%	KEV	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-03-17.