CVE-2026-53648 in FOSSBilling
Summary
by MITRE • 07/07/2026
FOSSBilling is a free, open-source billing and client management system. Prior to version 0.8.1, downloadable product files are stored using a deterministic filename-derived path. When an administrator uploads a file for a downloadable product, FOSSBilling stores the file as `md5(<original filename>)` under the uploads directory. Because the stored path depends only on the client-supplied filename, two different downloadable products, or product/order files, uploaded with the same original filename will resolve to the same stored file path. A later upload can overwrite an earlier upload, causing customers or administrators downloading the earlier product to receive the later file instead. Version 0.8.1 patches the issue. Some workarounds are available. Restrict the `servicedownloadable.manage` permission to fully trusted administrators only. As an operational mitigation, ensure downloadable product files use unique filenames before upload. This reduces accidental collisions but does not fully address the underlying issue.
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Analysis
by VulDB Data Team • 07/07/2026
This vulnerability in FOSSBilling represents a critical path traversal and file overwrite issue that stems from deterministic filename generation within the system's download management functionality. The flaw exists in how the software handles file storage for downloadable products, where each uploaded file is stored using only the md5 hash of the original filename as its storage path. This design creates a fundamental security weakness because it eliminates any form of randomization or unique identification in the file naming scheme, making the system inherently susceptible to collision attacks.
The technical implementation of this vulnerability directly violates security principles by creating predictable file paths that can be easily manipulated or exploited. When multiple administrators upload files with identical names, regardless of their intended purpose or source, the system's deterministic approach results in identical storage locations. This means that any subsequent upload with the same filename will overwrite the previously stored file, creating a scenario where legitimate customers might inadvertently receive malicious or incorrect files. The vulnerability is classified as a path traversal issue with elements of insecure direct object reference, as described in CWE-22 and CWE-639.
From an operational perspective, this vulnerability poses significant risks to both customer data integrity and system security. Customers who download files from different products or orders could receive incorrect software versions, potentially leading to compatibility issues, security vulnerabilities, or complete service disruptions. Administrators face the additional challenge of maintaining file integrity across multiple uploads, as they cannot rely on the system to prevent accidental overwrites. The impact extends beyond simple data corruption to include potential supply chain attacks where malicious actors could exploit this weakness to replace legitimate files with compromised versions.
The mitigation strategies provided address both immediate operational concerns and long-term architectural fixes. Restricting the servicedownloadable.manage permission to fully trusted administrators represents a defense-in-depth approach that limits the attack surface by controlling who can upload downloadable files. However, this workaround remains incomplete because it doesn't prevent accidental collisions in environments where multiple trusted users need upload access. The recommendation for unique filename enforcement serves as a temporary operational mitigation but fails to address the core architectural flaw in the file storage mechanism itself.
This vulnerability aligns with several ATT&CK techniques including T1059 Command and Scripting Interpreter and T1566 Impair Defenses, particularly when exploited by malicious actors who might upload replacement files to compromise system integrity. The deterministic nature of the storage approach makes it vulnerable to both accidental and intentional overwrites that could be leveraged for supply chain attacks or service disruption. Organizations using FOSSBilling should implement comprehensive monitoring of download directories and establish automated validation processes to detect potential file collisions. The vulnerability demonstrates the importance of proper randomization in file naming schemes as outlined in security best practices for preventing predictable resource locations and maintaining data integrity across file management systems.
The issue also highlights broader concerns about open source software security practices, particularly regarding the implementation of secure file handling mechanisms. Many FOSS projects lack robust security testing for file management components, creating vulnerabilities that could be exploited in production environments. The fix implemented in version 0.8.1 likely involves introducing randomization or additional entropy into the filename generation process to ensure unique storage paths regardless of original filename input, which aligns with established security guidelines for preventing predictable resource access patterns and maintaining proper file isolation within web applications.