What is the CVSS score of CVE-2026-4021?

CVE-2026-4021 has a CVSS 3.1 base score of 8.1 (High). CVSS vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H. EPSS exploitation probability: 0.1%.

Which versions of PHP are affected by CVE-2026-4021?

The Contest Gallery WordPress plugin contains a critical authentication bypass vulnerability that could allow attackers to seize administrator accounts and gain complete control of affected websites.

How to fix or mitigate CVE-2026-4021?

Within 24 hours: Audit all WordPress instances for Contest Gallery plugin presence and verify if RegMailOptional=1 is enabled; isolate affected sites or disable the plugin immediately. Within 7 days: If the plugin is business-critical, implement WAF rules to block suspicious registration patterns and enforce network segmentation to limit admin access. Within 30 days: Monitor for vendor patch release; evaluate alternative plugins with equivalent functionality and establish a timeline for migration.

PHP CVE-2026-4021

EUVD-2026-14654 HIGH

Improper Authentication (CWE-287)

2026-03-23 Wordfence

GHSA-m4rm-grq4-j8wp

WordPress PHP Authentication Bypass

8.1

CVSS 3.1 · NVD

Severity by source

NVD PRIMARY

8.1 HIGH

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

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

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

Attack Vector

Network

Attack Complexity

High

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Lifecycle Timeline

Re-analysis Queued

Apr 24, 2026 - 16:37 vuln.today

cvss_changed

EUVD ID Assigned

Mar 23, 2026 - 23:45 euvd

EUVD-2026-14654

Analysis Generated

Mar 23, 2026 - 23:45 vuln.today

CVE Published

Mar 23, 2026 - 23:25 nvd

HIGH 8.1

DescriptionCVE.org

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., 1poc@example.test), 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.

AnalysisAI

The Contest Gallery plugin for WordPress contains an authentication bypass vulnerability that allows unaattacked attackers to take over administrator accounts and gain complete site control. All versions up to and including 28.1.5 are affected when the non-default RegMailOptional=1 setting is enabled. The vulnerability exploits MySQL type coercion by registering with specially crafted email addresses to overwrite admin activation keys, then using an unauthenticated login endpoint to authenticate as the target user. With a CVSS score of 8.1 and high attack complexity (AC:H), this represents a critical risk for sites using the vulnerable configuration.

Technical ContextAI

This vulnerability affects the Contest Gallery plugin for WordPress (CPE: cpe:2.3:a:contest-gallery:contest_gallery_–_upload_&_vote_photos,_media,_sell_with_paypal_&_stripe:*:*:*:*:*:*:*:*). The root cause is CWE-287 (Improper Authentication) stemming from a type confusion issue in users-registry-check-after-email-or-pin-confirmation.php at line 153. The code uses a user-supplied email string in a WHERE ID = %s SQL clause where a numeric user ID is expected. When MySQL performs implicit type coercion, an email like '1poc@example.test' is converted to integer 1, causing the query to target the admin user (typically ID 1) instead of the registering user. This overwrites the admin's user_activation_key field. The vulnerability chain is completed by the post_cg1l_login_user_by_key AJAX action in ajax-functions-frontend.php at line 204, which allows unauthenticated key-based login without proper validation, enabling the attacker to authenticate as the compromised admin account using the activation key they controlled.

RemediationAI

Immediately upgrade Contest Gallery plugin to version 28.1.6 or later, which addresses this authentication bypass vulnerability. The patch changeset is documented at https://plugins.trac.wordpress.org/changeset?old_path=/contest-gallery/tags/28.1.5&new_path=/contest-gallery/tags/28.1.6. If immediate patching is not feasible, disable the RegMailOptional=1 setting in the plugin configuration to eliminate the attack vector, as this vulnerability requires this non-default option to be enabled. Additionally, implement web application firewall rules to monitor and block suspicious user registration attempts with email addresses beginning with numeric characters, particularly those matching low user IDs like 1 or 2 which typically correspond to administrator accounts. Review existing user accounts for suspicious registrations with emails starting with numbers and examine authentication logs for unexpected admin login activity using the post_cg1l_login_user_by_key AJAX action.