CVE-2026-53640 in FOSSBilling
Summary
by MITRE • 07/07/2026
FOSSBilling is a free, open-source billing and client management system. Prior to version 0.8.0, low-privileged staff accounts may read sensitive data via admin API endpoints that lack permission checks. While sibling write endpoints correctly enforce fine-grained permissions, the corresponding read endpoints have no authorization guards. Version 0.8.0 contains a fix. Some workarounds are available. Restrict staff accounts to only those who need access to sensitive data and/or use a reverse proxy or WAF to restrict access to the affected endpoints.
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Analysis
by VulDB Data Team • 07/07/2026
The FOSSBilling vulnerability represents a critical authorization flaw that undermines the security posture of this open-source billing and client management system. This issue affects versions prior to 0.8.0 and stems from an inconsistent implementation of access controls within the administrative API endpoints. The vulnerability specifically targets low-privileged staff accounts that should not have access to sensitive data but can exploit read endpoints that lack proper permission validation mechanisms.
The technical flaw manifests as a classic authorization bypass where the system correctly implements permission checks for write operations but fails to enforce similar controls for read operations. This creates a scenario where unauthorized users with minimal privileges can access confidential information through API calls that should be restricted to administrators or higher-privileged roles. The vulnerability operates at the application layer and can be exploited through direct API endpoint manipulation, making it particularly dangerous in environments where staff accounts are not properly segregated.
The operational impact of this vulnerability extends beyond simple data exposure, as it enables potential attackers with access to low-privileged staff accounts to gather sensitive client information, billing details, and system configuration data. This could lead to financial fraud, privacy violations, and compliance breaches that would be particularly damaging in regulated environments. The flaw also represents a violation of the principle of least privilege, where users have access to resources beyond their intended scope of responsibility.
This vulnerability aligns with CWE-285, which addresses improper authorization issues in software systems, and maps to ATT&CK technique T1078 for valid accounts and T1566 for credential harvesting. The inconsistency between write and read endpoint protections creates a security gap that attackers can exploit to escalate privileges or gain unauthorized access to sensitive data. Organizations using FOSSBilling should immediately implement the version 0.8.0 update to resolve this issue, while also applying additional mitigations such as role-based access control restrictions and network-level protections through reverse proxies or web application firewalls.
The recommended remediation approach includes restricting staff accounts to only those who absolutely require access to sensitive data, implementing proper role-based access controls, and deploying network security measures to filter API requests. These measures should be complemented by regular security audits and monitoring of API usage patterns to detect potential exploitation attempts. The vulnerability serves as a reminder of the critical importance of consistent authorization implementation across all application functions, particularly in systems handling sensitive financial and personal data.