CVE-2026-73403 in User Registration Plugin
Summary
by MITRE • 08/13/2026
Unauthenticated Broken Access Control in User Registration <= 5.2.6 versions.
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Analysis
by VulDB Data Team • 08/17/2026
This vulnerability represents a critical breakdown in access control mechanisms within user registration systems, specifically affecting versions up to and including 5.2.6. The flaw allows unauthorized users to bypass authentication requirements and potentially register accounts without proper authorization, fundamentally compromising the system's security posture. Such vulnerabilities typically arise from insufficient validation of user permissions or improper session management during the registration process.
The technical implementation of this weakness often involves missing input validation checks, inadequate authorization controls, or flawed logic in the registration workflow that permits arbitrary account creation. Attackers can exploit this by sending specially crafted requests that bypass normal registration restrictions, potentially creating multiple accounts or registering with elevated privileges. This type of vulnerability falls under the broader category of broken access control as defined by CWE-284, which specifically addresses insufficient access control mechanisms in software systems.
The operational impact of unauthenticated broken access control during user registration can be severe and multifaceted. An attacker gaining unauthorized registration capabilities can create numerous malicious accounts, potentially leading to spamming activities, denial of service through account exhaustion, or even privilege escalation if the system allows for administrative account creation through the registration process. The vulnerability can also enable credential stuffing attacks where attackers register using stolen credentials from other systems. From an attacker's perspective, this represents a low-hanging fruit opportunity that can provide initial access to the system and potentially serve as a foothold for more sophisticated attacks.
Security practitioners should implement comprehensive mitigations including robust input validation, proper authentication checks at every registration endpoint, rate limiting mechanisms to prevent account flooding, and thorough authorization verification during user creation processes. The implementation should follow established security frameworks such as the OWASP Top Ten and adhere to NIST cybersecurity guidelines for access control management. Additionally, organizations should conduct regular penetration testing and vulnerability assessments focusing on authentication flows, particularly around user registration and account management functionalities.
From an ATT&CK framework perspective, this vulnerability maps to multiple techniques including T1078 for valid accounts and T1566 for credential harvesting. The exploitation typically follows a pattern where attackers first identify the vulnerable registration endpoint, then craft requests that bypass normal authentication checks. This type of attack often occurs during the initial reconnaissance phase when threat actors are exploring system boundaries and identifying potential entry points. Organizations should implement network monitoring to detect unusual registration patterns and establish automated alerting for suspicious account creation activities. The vulnerability also highlights the importance of principle of least privilege implementation, ensuring that even legitimate users cannot perform actions beyond their assigned permissions during the registration process.
The remediation approach requires a multi-layered strategy combining application-level fixes with infrastructure-level protections. Code reviews should specifically focus on authentication flows and ensure all registration endpoints implement proper authorization checks. The system should enforce strict validation of user inputs and maintain audit logs for all registration activities. Regular security updates and patch management processes become critical to prevent exploitation of known vulnerabilities in older versions. Organizations should also consider implementing additional security controls such as CAPTCHA mechanisms, IP address monitoring, and behavioral analytics to detect and prevent automated exploitation attempts.