dbcve.org
Improper AuthenticationWeakness · CWE-287

CVE-2026-4021

HIGH · 8.1 CVSS v3.1 Published 2026-03-24
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
90/100
Remediation priority · Urgent
Remotely reachable No privileges 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
The Contest Gallery plugin for WordPress is vulnerable to an authentication bypass leading to admin account takeover in all versions up to, and including, 28.1.5. This is due to the email confirmation handler in `users-registry-check-after-email-or-pin-confirmation.php` using the user's email string in a `WHERE ID = %s` clause instead of the numeric user ID, combined with an unauthenticated key-based login endpoint in `ajax-functions-frontend.php`. When the non-default `RegMailOptional=1` setting is enabled, an attacker can register with a crafted email starting with the target user ID (e.g., `[email protected]`), trigger the confirmation flow to overwrite the admin's `user_activation_key` via MySQL integer coercion, and then use the `post_cg1l_login_user_by_key` AJAX action to authenticate as the admin without any credentials. This makes it possible for unauthenticated attackers to take over any WordPress administrator account and gain full site control.

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

The Contest Gallery plugin has an authentication bypass vulnerability caused by a type confusion flaw in the email confirmation handler. When the non-default RegMailOptional=1 setting is enabled, the handler incorrectly uses a user's email string in a WHERE ID = %s SQL clause, allowing MySQL integer coercion. An attacker registers with a crafted email like '[email protected]' to overwrite the target admin's user_activation_key, then authenticates via the unauthenticated post_cg1l_login_user_by_key AJAX action.

MitigationUpdate the Contest Gallery plugin to version 28.1.6 or later. As a temporary mitigation, disable the RegMailOptional setting if possible, but note that this is a non-default setting.

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

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
High
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

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. Confirm Contest Gallery plugin installation and version
    In WordPress admin, go to Plugins > Installed Plugins and locate Contest Gallery, noting the version number. Alternatively, check the plugin directory files for the main PHP file containing version info.
    Affected if Installed version is lower than 28.1.6 and the plugin is active
  2. Verify RegMailOptional setting is enabled
    Access the plugin settings area in WordPress admin (Contest Gallery > Settings > Registration or similar). Look for a RegMailOptional or 'Optional email confirmation' setting and determine if it is enabled (set to 1 or checked).
    Affected if RegMailOptional is set to 1 (enabled); if disabled, the vulnerability path is not reachable
  3. Check AJAX endpoint accessibility
    Verify the post_cg1l_login_user_by_key AJAX action is accessible to unauthenticated users by examining WordPress AJAX setup or testing the endpoint (wp-admin/admin-ajax.php?action=post_cg1l_login_user_by_key) without providing authentication cookies.
    Affected if The AJAX endpoint responds without requiring authentication (returns a valid JSON response rather than a 403 or login redirect)
  4. Review email-based SQL query handling
    If you have access to plugin source code, locate the email confirmation handler and check if user-supplied email is being used directly in a SQL WHERE clause with integer placeholder (e.g., WHERE ID = %s).
    Affected if The code uses the email field in a context expecting an integer ID without proper type casting

The environment is affected if Contest Gallery plugin version is below 28.1.6 AND RegMailOptional=1 is enabled AND the unauthenticated AJAX login action is accessible.

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.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Update the Contest Gallery plugin to version 28.1.6 or later. As a temporary mitigation, disable the RegMailOptional setting if possible, but note that this is a non-default setting.

Have this fixed Scoped from the published advisory
  • Consultation2.0 h
  • Implementation3.0 h
  • Testing2.0 h
  • Review / QA1.0 h
8.0 hours of engineering $1,420
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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-2026-4021 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