CVE-2025-46387 in MediaBrowser
Summary
by MITRE • 08/06/2025
CWE-639 Authorization Bypass Through User-Controlled Key
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Analysis
by VulDB Data Team • 05/14/2026
CWE-639 represents a critical authorization bypass vulnerability that occurs when an application permits unauthorized access to resources through user-controlled keys or identifiers. This weakness enables attackers to manipulate authentication mechanisms by controlling keys that should remain protected, effectively circumventing intended access controls. The vulnerability stems from insufficient validation of user inputs used as keys for resource access, allowing malicious actors to exploit the system's trust in these identifiers. Such flaws commonly manifest in web applications where session tokens, API keys, or resource identifiers are improperly validated or sanitized before being used for access decisions. The underlying technical flaw typically involves inadequate input validation, insufficient key verification processes, or improper key management practices that permit user-controllable data to influence authorization decisions directly.
The operational impact of CWE-639 vulnerabilities can be severe and far-reaching across multiple system components and data assets. Attackers exploiting this weakness can gain unauthorized access to sensitive information, perform privileged operations, or escalate their privileges within the system. The vulnerability allows for lateral movement and privilege escalation attacks, as compromised keys may grant access to multiple resources or system functions. Depending on the application architecture, attackers might access user accounts, administrative interfaces, or critical system resources without proper authentication. The risk is particularly elevated when keys are used for session management, API access, or database record identification, as these components often contain sensitive data or control critical system functions. This weakness can also facilitate data exfiltration, system compromise, and unauthorized modifications to protected resources, making it a significant concern for organizations handling sensitive information.
Mitigation strategies for CWE-639 vulnerabilities must address both the immediate technical flaws and underlying architectural issues that enable unauthorized key manipulation. Implementing robust input validation and sanitization processes ensures that user-controlled keys undergo proper verification before being accepted for authorization decisions. Applications should employ server-side key validation mechanisms that independently verify key authenticity and integrity, rather than relying solely on client-side controls or user-provided data. Strong key management practices including random key generation, secure storage, and proper key lifecycle management help prevent attackers from predicting or manipulating access identifiers. Access control implementations should utilize role-based access control models with proper authorization checks that do not depend on user-controllable inputs for determining resource access. Security measures should include logging and monitoring of key usage patterns to detect anomalous behavior that might indicate exploitation attempts. Organizations should also implement principle of least privilege access controls and regularly audit authorization mechanisms to identify potential bypass opportunities. These defensive measures align with security best practices outlined in industry standards and help protect against the specific attack vectors associated with user-controlled key authorization bypass scenarios.
This vulnerability type corresponds to several ATT&CK tactics including privilege escalation and lateral movement, where attackers leverage compromised keys to access additional resources or elevate their privileges. The weakness is frequently observed in applications with poor input validation, inadequate session management, or weak API security implementations. Security professionals should consider CWE-639 when analyzing authorization mechanisms and conducting vulnerability assessments to prevent attackers from exploiting user-controlled identifiers for unauthorized access. The remediation process requires comprehensive review of all key-based access control implementations and verification that proper authorization checks are in place to prevent bypass opportunities.