CVE-2015-5954 in ownCloud Server
Summary
by MITRE
The virtual filesystem in ownCloud Server before 6.0.9, 7.0.x before 7.0.7, and 8.0.x before 8.0.5 does not consider that NULL is a valid getPath return value, which allows remote authenticated users to bypass intended access restrictions and gain access to users files via a sharing link to a file with a deleted parent folder.
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Analysis
by VulDB Data Team • 04/01/2025
The vulnerability described in CVE-2015-5954 represents a critical access control flaw within the virtual filesystem implementation of ownCloud Server across multiple affected versions. This issue stems from the improper handling of NULL return values from the getPath function within the virtual filesystem layer, creating a pathway for authenticated attackers to circumvent intended file access restrictions. The vulnerability specifically manifests when users attempt to access shared files through links that reference files within deleted parent folders, exploiting a logical gap in the system's file path resolution mechanism.
The technical root cause of this vulnerability lies in the virtual filesystem's failure to properly validate and handle NULL return values from the getPath function, which is a fundamental component responsible for determining file paths within the system's virtualized file structure. According to CWE-252, this represents an improper validation of a return value, where the system assumes that all return values from a function will be valid and non-null. When a file exists within a deleted parent folder structure, the getPath function may legitimately return NULL, but the virtual filesystem implementation does not account for this scenario, leading to unexpected behavior that can be exploited by attackers.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it allows remote authenticated users to gain unauthorized access to files belonging to other users within the ownCloud environment. This represents a significant breach of the principle of least privilege and can result in data leakage, unauthorized file access, and potential compromise of sensitive information stored within the system. The vulnerability specifically affects users who have access to shared links, making it particularly dangerous in environments where users share files with others through the platform's built-in sharing mechanisms.
Attackers can exploit this vulnerability by creating or manipulating shared links to files within deleted parent folders, leveraging the NULL return value handling issue to bypass access controls that should normally prevent unauthorized file access. This attack vector operates through the normal sharing workflow of ownCloud, making it difficult to detect and prevent through traditional security measures. The vulnerability affects multiple version lines of ownCloud Server, indicating a systemic issue within the virtual filesystem implementation that required patching across different major releases.
The mitigation strategy for this vulnerability involves updating to the patched versions of ownCloud Server, specifically versions 6.0.9, 7.0.7, and 8.0.5, which contain the necessary fixes to properly handle NULL return values from the getPath function. Organizations should also implement network monitoring to detect unusual access patterns related to shared files and deleted folder structures, as well as conduct regular security assessments of their ownCloud implementations. This vulnerability aligns with ATT&CK technique T1078 which covers legitimate credentials and privileges, as it exploits legitimate sharing functionality to gain unauthorized access to files. System administrators should also review and audit existing shared links and file permissions to ensure no unauthorized access has occurred through this vulnerability before applying the patches.