CVE-2026-106603 in HollerBox Plugin
Summary
by MITRE • 10/08/2026
Authorization Bypass Through User-Controlled Key vulnerability in Groundhogg HollerBox holler-box allows Exploiting Incorrectly Configured Access Control Security Levels.This issue affects HollerBox: from n/a through 2.3.14.
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Analysis
by VulDB Data Team • 10/08/2026
The identified vulnerability represents a critical failure in access control mechanisms within the HollerBox component of Groundhogg, specifically classified as an Authorization Bypass Through User-Controlled Key. This flaw allows attackers to manipulate input parameters that serve as keys for accessing sensitive resources or performing administrative actions without proper authentication or authorization checks. The root cause lies in the application's reliance on user-supplied data to determine access levels rather than enforcing server-side security policies based on verified session states and role-based permissions. By exploiting this misconfiguration, an attacker can escalate privileges from a standard user account to that of an administrator or gain unauthorized access to restricted functionalities, effectively bypassing intended security boundaries.
From a technical perspective, the vulnerability stems from insufficient validation of keys used for authorization decisions. In many web applications, identifiers such as session tokens, resource IDs, or configuration parameters are passed via URLs, form fields, or API payloads. When these values are directly mapped to access control logic without verifying their legitimacy against the current user's profile, it creates an opportunity for unauthorized manipulation. An attacker can modify these keys to reference resources belonging to other users or system-level functions that should not be accessible. This type of flaw is commonly associated with Broken Access Control vulnerabilities where the application fails to enforce proper separation between data and functionality, allowing low-privileged entities to interact with high-privilege operations.
The operational impact of this vulnerability is severe, particularly for organizations using HollerBox versions from n/a through 2.3.14. Successful exploitation can lead to complete compromise of user accounts, including the ability to modify subscriber lists, send unauthorized marketing emails, or access sensitive customer data stored within the platform. In a business context involving email marketing and automation, this could result in significant reputational damage, regulatory penalties under laws such as GDPR or CCPA due to data breaches, and potential misuse for spamming campaigns that harm sender reputation scores. Furthermore, if administrative functions are exposed, attackers may install malicious plugins, alter site configurations, or use the server resources for further attacks against other systems within the network perimeter.
This vulnerability aligns with CWE-284 Improper Access Control and is mapped to MITRE ATT&CK technique T1078 Valid Accounts, where adversaries leverage legitimate credentials or manipulate access mechanisms to maintain persistence and escalate privileges. It also relates to CWE-639 Authorization Bypass Through User-Controlled Key, highlighting the specific mechanism of exploitation through manipulated identifiers. To mitigate this risk, immediate action is required by upgrading HollerBox to a version later than 2.3.14 where these access control checks have been hardened. Developers should implement strict server-side validation for all authorization keys, ensuring that every request verifies the user's current role and permissions against an authoritative source rather than trusting client-supplied data. Additionally, implementing principle of least privilege in application design and regularly auditing access control logic can prevent similar vulnerabilities from being introduced or exploited in future updates.