Unauthenticated Broken Access Control in MailChimp Block

Executive Summary

CVE-2026-56063 is a Broken Access Control vulnerability in the WordPress MailChimp Block Plugin versions 1.1.15 and earlier.

This vulnerability allows unauthenticated users to perform actions with higher privileges because the plugin lacks proper authorization, authentication, or nonce token checks.

It is classified as a high-risk issue with a CVSS score of 8.3 and falls under the OWASP Top 10 category A1: Broken Access Control.

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Detection Guidance

The vulnerability in the WordPress MailChimp Block Plugin versions 1.1.15 and earlier is due to missing authorization, authentication, or nonce token checks, allowing unauthenticated users to perform privileged actions.

There is no specific detection command or network signature provided in the available resources.

However, monitoring for unusual or unauthorized access attempts to the MailChimp Block plugin endpoints or suspicious HTTP requests targeting the plugin could help identify exploitation attempts.

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Impact Analysis

This vulnerability can allow attackers to perform unauthorized actions on affected websites without needing to authenticate.

Because the vulnerability affects thousands of websites using the vulnerable plugin versions, exploitation could lead to data manipulation, service disruption, or unauthorized access to sensitive information.

The impact includes potential loss of confidentiality, integrity, and availability of the affected systems.

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Compliance Impact

The vulnerability in the MailChimp Block plugin allows unauthenticated users to bypass access controls, potentially leading to unauthorized access to sensitive data or functionality.

Such unauthorized access could result in violations of data protection regulations like GDPR or HIPAA, which require strict controls over access to personal and sensitive information.

Therefore, if exploited, this vulnerability may compromise compliance with these standards by failing to adequately protect data confidentiality, integrity, and availability.

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Mitigation Strategies

Immediate mitigation steps include updating the WordPress MailChimp Block Plugin to version 1.1.16 or later, where the vulnerability has been patched.

Until the update can be applied, it is recommended to implement the mitigation rule provided by Patchstack to block attacks targeting this vulnerability.

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