CVE-2023-39736 in Line
Summary
by MITRE • 10/25/2023
The leakage of the client secret in Fukunaga_memberscard Line 13.6.1 allows attackers to obtain the channel access token and send crafted broadcast messages.
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Analysis
by VulDB Data Team • 01/26/2026
The vulnerability identified as CVE-2023-39736 represents a critical security flaw in the Fukunaga_memberscard Line 13.6.1 application that stems from improper handling of client secrets within the authentication and authorization framework. This issue falls under the broader category of credential exposure vulnerabilities, specifically addressing the insecure storage or transmission of sensitive authentication tokens that should remain protected from unauthorized access. The flaw manifests when client secrets are inadvertently exposed or leaked within the application's codebase or configuration files, creating an avenue for malicious actors to gain unauthorized access to the system's communication channels.
The technical implementation of this vulnerability allows attackers to extract channel access tokens that are typically used for authenticating API requests to the LINE messaging platform. When client secrets are improperly managed or stored in accessible locations, they become susceptible to exploitation through various attack vectors including code inspection, network traffic analysis, or privilege escalation techniques. The vulnerability specifically impacts the LINE messaging infrastructure integration where the application relies on these tokens to send broadcast messages to users. This exposure creates a direct pathway for unauthorized message broadcasting, potentially enabling spam campaigns, phishing attacks, or other malicious communication activities that can affect both the application's integrity and user privacy.
The operational impact of this vulnerability extends beyond simple credential theft, as it enables attackers to leverage the legitimate application access to perform unauthorized broadcasting activities. This capability can be exploited for mass messaging campaigns that may include malicious content, social engineering attempts, or promotional activities that could damage the application's reputation and user trust. The vulnerability directly violates security principles outlined in the OWASP Top Ten, particularly focusing on insufficient logging and monitoring, and represents a clear violation of the principle of least privilege. Attackers can utilize the obtained access tokens to send messages to all users within the channel, potentially reaching thousands of recipients with malicious payloads or unwanted communications.
From a defensive standpoint, this vulnerability requires immediate remediation through comprehensive code review processes to identify and eliminate any exposed secrets, implementation of proper secret management practices, and deployment of automated scanning tools to detect credential leakage. Organizations should implement robust key rotation policies, utilize secure configuration management systems, and establish monitoring mechanisms to detect unauthorized access attempts. The vulnerability demonstrates the critical importance of adhering to security best practices as outlined in NIST SP 800-53 controls for access control and cryptography, particularly emphasizing the need for secure credential storage and management. Mitigation strategies should include deployment of secret management solutions such as HashiCorp Vault or AWS Secrets Manager, implementation of automated security scanning during development lifecycle, and establishment of proper access controls and audit trails to prevent unauthorized access to sensitive information.
The attack surface for this vulnerability aligns with several ATT&CK techniques including credential access through exposed credentials, privilege escalation through unauthorized access to legitimate accounts, and command and control through messaging platform abuse. Security teams should implement network monitoring to detect unusual broadcasting patterns and establish incident response procedures specifically addressing credential exposure events. The vulnerability serves as a reminder of the critical need for security awareness training and the implementation of secure coding practices throughout the software development lifecycle. Organizations must ensure that all authentication tokens and secrets are properly protected through encryption, access controls, and regular security assessments to prevent similar exposure scenarios that could compromise user communications and system integrity.