CVE-2022-4036 in Appointment Hour Booking Plugin
Summary
by MITRE • 11/30/2022
The Appointment Hour Booking plugin for WordPress is vulnerable to CAPTCHA bypass in versions up to, and including, 1.3.72. This is due to the use of insufficiently strong hashing algorithm on the CAPTCHA secret that is also displayed to the user via a cookie.
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Analysis
by VulDB Data Team • 04/09/2026
The CVE-2022-4036 vulnerability affects the Appointment Hour Booking plugin for WordPress, representing a critical security flaw that undermines the plugin's anti-spam protection mechanisms. This vulnerability exists in versions up to and including 1.3.72, making a significant portion of WordPress installations potentially susceptible to abuse. The core issue lies in the plugin's implementation of CAPTCHA protection, which is designed to prevent automated booking submissions and spam attacks on appointment systems. When users attempt to schedule appointments through the plugin's interface, the system should verify their human identity through CAPTCHA validation before processing the request. However, the flaw allows malicious actors to circumvent this protection entirely.
The technical root cause of this vulnerability stems from the use of insufficiently strong hashing algorithms for generating and storing CAPTCHA secrets. Specifically, the plugin employs weak cryptographic methods that fail to provide adequate entropy and security for the secret values used in the CAPTCHA validation process. Furthermore, the vulnerability is exacerbated by the fact that these CAPTCHA secrets are stored in cookies and are also displayed directly to users, creating a dangerous combination that exposes the underlying cryptographic weakness. The combination of weak hashing and exposed secret values creates a scenario where an attacker can easily reverse-engineer or predict the CAPTCHA validation tokens, effectively bypassing the entire anti-spam mechanism. This represents a fundamental flaw in the plugin's security architecture and violates standard cryptographic practices that require strong, unpredictable hashing algorithms for sensitive security tokens.
The operational impact of CVE-2022-4036 is severe and multifaceted, particularly for organizations that rely on appointment booking systems for critical services. Attackers can exploit this vulnerability to perform automated spam booking campaigns, potentially overwhelming appointment slots and disrupting legitimate service delivery. The bypass capability allows malicious actors to submit unlimited booking requests without CAPTCHA verification, leading to resource exhaustion and service degradation. In high-traffic environments, this vulnerability could enable denial of service conditions where legitimate users cannot secure appointments due to automated spam submissions. The exposure of CAPTCHA secrets through cookies also increases the risk of session hijacking and other related attacks, as the weak hashing implementation makes it trivial for attackers to obtain valid tokens. This vulnerability directly impacts the plugin's intended security posture, which is designed to protect against automated abuse and maintain the integrity of appointment scheduling systems.
Mitigation strategies for CVE-2022-4036 must address both the immediate security gap and implement long-term defensive measures. The primary recommendation is to upgrade to a patched version of the Appointment Hour Booking plugin that addresses the cryptographic weaknesses in CAPTCHA secret handling. Organizations should also implement additional monitoring and rate-limiting mechanisms to detect and prevent abnormal booking patterns that could indicate exploitation attempts. Network-level controls such as web application firewalls can help identify and block suspicious CAPTCHA bypass attempts, while logging and audit trails should be enhanced to track all booking activities for security analysis. The vulnerability highlights the importance of proper cryptographic implementation and adherence to security standards, particularly those related to hash function selection and secret management. From an ATT&CK framework perspective, this vulnerability maps to techniques involving credential access and privilege escalation through weak cryptographic implementations, while CWE categorization places it within the realm of weak cryptographic hashing and improper secret handling. Organizations should also consider implementing multi-factor authentication for critical booking systems and regularly reviewing their plugin security posture to prevent similar vulnerabilities from emerging in other components of their WordPress infrastructure.