dbcve.org
Open FormsApplication · Maykinmedia

CVE-2026-28803

MEDIUM · 6.5 CVSS v3.1 Published 2026-03-11
Fix available
A fix is available. Upgrade to 3.3.13 / 3.4.5 or later.
See remediation →
71/100
Remediation priority · Elevated
Remotely reachable Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Open Forms contains an Insecure Direct Object Reference (IDOR) vulnerability in the cosign workflow. The submission reference codes used in deep-links for cosigning can be guessed or manipulated, allowing authenticated users to access arbitrary submission data they don't own. This occurs because the lookup mechanism doesn't verify that the requesting user has permission to access the specific submission.

MitigationUpgrade to Open Forms version 3.3.13 or 3.4.5, which implements proper authorization checks to ensure users can only access submissions they are authorized to view.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Open FormsApplication
Affected:< 3.3.13>= 3.4.0, < 3.4.5

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check installed Open Forms version
    Locate the installed version of Maykinmedia Open Forms. This is typically visible in the admin interface under 'Version' or 'System information', or can be found via command line if you have shell access to the deployment.
    Affected if The installed version is less than 3.3.13, or greater than or equal to 3.4.0 but less than 3.4.5
  2. Identify if cosign workflow is in use
    Determine whether the cosigning functionality is enabled or has been used in your Open Forms deployment. Check the form configurations or cosign-related settings in the admin panel to see if any forms have cosigning enabled.
    Affected if Cosign functionality is enabled or any submissions have been made using the cosign workflow in the affected version range
  3. Locate submission reference code patterns
    Examine the URL structure or API endpoints used for cosigning deep-links. These typically contain submission reference codes that can be manipulated. Look for endpoints related to 'cosign' or 'co-sign' in your web server logs or application routing configuration.
    Affected if Submission reference codes in cosign URLs follow a predictable or sequential pattern rather than using secure random identifiers

A defender is affected if running an Open Forms version in the vulnerable range (< 3.3.13 or >= 3.4.0, < 3.4.5) AND the cosign workflow feature is in use, allowing unauthorized access to submission data via manipulated reference codes.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 3.3.13 / 3.4.5 or later
Fixed in 3.3.133.4.5
Interim mitigation

Upgrade to Open Forms version 3.3.13 or 3.4.5, which implements proper authorization checks to ensure users can only access submissions they are authorized to view.

Recommended fix High confidence

3.3.13 (for 3.3.x branch) or 3.4.5 (for 3.4.x branch)

  1. Identify the currently installed version of Open Forms by checking the application or deployment configuration
  2. If running a version < 3.3.13, plan upgrade to version 3.3.13 or later (3.3.x stable branch)
  3. If running version >= 3.4.0 and < 3.4.5, plan upgrade to version 3.4.5 or later (3.4.x stable branch)
  4. Execute the upgrade using the appropriate method for your deployment (e.g., package manager, container update, or direct installation)
  5. After upgrade, verify that the submission reference validation has been fixed by testing the cosign flow with both valid and modified submission codes
  6. Confirm that unauthorized access to arbitrary submissions is no longer possible

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Open Forms Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing3.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,490
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-28803 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data