CVE-2026-72834 in Filebrowser
Summary
by MITRE • 08/14/2026
filebrowser before 2.63.19 contains a permission bypass in the /api/resources endpoint. The checksum (?checksum=) branch of resourceGetHandler reads the entire file to compute a digest and returns it without performing a Perm.Download check (unlike the sibling raw, preview, and subtitle paths). As a result, an authenticated user provisioned with Perm.Download=false can obtain a content-hash oracle for any same-scope file (md5/sha1/sha256/sha512), enabling confirmation of known/guessed content, change detection, and offline brute-force of low-entropy files. This is an incomplete fix of CVE-2026-35606; it bypasses only the Download permission and does not defeat scope/path authorization.
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Analysis
by VulDB Data Team • 08/14/2026
The vulnerability in filebrowser versions prior to 2.63.19 represents a critical permission bypass flaw within the /api/resources endpoint that undermines the application's access control mechanisms. This issue specifically affects the resourceGetHandler function's checksum processing branch, where the system computes cryptographic digests of files without proper authorization checks. The vulnerability stems from an inconsistent implementation of permission controls where the checksum computation path operates independently from other file access routes such as raw, preview, and subtitle endpoints that correctly enforce Perm.Download checks. This creates a scenario where authenticated users can leverage the content-hash oracle functionality to gain unauthorized insights into file contents, effectively bypassing the intended security boundaries while maintaining the existing scope-based authorization controls.
The technical exploitation of this vulnerability occurs through the checksum parameter (?checksum=) which triggers a code path that reads entire files to compute digest values including md5, sha1, sha256, and sha512 hashes. Unlike other file access methods within the same endpoint, this particular branch fails to validate whether the authenticated user possesses the necessary download permissions before proceeding with file processing. The flaw exists at the application logic level where permission validation is selectively applied, creating a bypass condition that allows attackers to perform content verification attacks against files within their accessible scope. This represents a partial regression from previous security measures as it addresses only the download permission aspect while leaving other authorization controls intact.
Operationally, this vulnerability enables significant reconnaissance and attack capabilities for authenticated users who have been granted limited permissions but lack explicit download rights. The content-hash oracle functionality allows attackers to confirm known or guessed file contents, perform change detection across time periods, and execute offline brute-force attacks against low-entropy files within the accessible scope. This capability can be particularly dangerous in environments where sensitive documents are stored, as it provides attackers with a method to verify file integrity and potentially identify valuable targets for further exploitation. The vulnerability does not compromise the overall authorization model but rather exploits an implementation gap that allows unauthorized content analysis while maintaining existing scope restrictions.
Security professionals should recognize this issue as a variant of permission bypass vulnerabilities classified under CWE-285, which deals with improper authorization in access control systems. The attack vector aligns with techniques described in the ATT&CK framework under privilege escalation and defense evasion tactics, where adversaries leverage application logic flaws to gain unauthorized information access. Organizations should implement immediate mitigations including updating to filebrowser version 2.63.19 or later, which addresses this specific bypass condition by ensuring all checksum computation paths properly validate download permissions before processing files. Additionally, security teams should review their permission configurations to ensure that users with limited access rights cannot inadvertently gain information disclosure capabilities through similar implementation gaps in other application components.
The vulnerability demonstrates the importance of consistent access control implementation across all code paths within applications, particularly in API endpoints where multiple operations may share common underlying functions. It highlights how seemingly minor implementation differences can create significant security implications and emphasizes the need for comprehensive permission validation testing. The fix implemented in version 2.63.19 represents a proper remediation that ensures all file access methods within the resources endpoint consistently enforce download permissions, preventing unauthorized content analysis while preserving legitimate scope-based authorization controls. Organizations should conduct thorough security reviews of their applications to identify similar permission bypass conditions that may exist across different components and ensure that access control validation is uniformly applied throughout the application architecture.