CVE-2026-72835 in filebrowser
Summary
by MITRE • 08/14/2026
filebrowser versions before v2.63.21 fail to canonicalize paths before evaluating access rules, allowing authenticated users to bypass administrator-defined deny rules using case-variant or backslash-separated paths. Attackers can request files with alternate path representations that match no rule but resolve to the same filesystem object, gaining unauthorized access to denied files within their scope.
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Analysis
by VulDB Data Team • 08/14/2026
This vulnerability exists in filebrowser versions prior to v26321 where the application fails to properly canonicalize file paths before processing access control rules. The core technical flaw resides in how the system handles path normalization, specifically when dealing with case-insensitive file systems or different path separators. When users submit requests for files using alternate representations such as mixed case variants or backslash-separated paths, the system evaluates these against access rules without first converting them to their canonical form. This path traversal behavior creates a fundamental gap in the authorization mechanism that allows authenticated users to bypass administrator-defined deny rules.
The operational impact of this vulnerability is significant as it enables attackers to gain unauthorized access to files that should be restricted based on their access control policies. An attacker can exploit this by crafting requests using path variants that appear to be different from the actual file paths but resolve to the same filesystem object through path canonicalization. For example, a rule might deny access to /home/user/documents/secret.txt but an attacker could request /HOME/USER/DOCUMENTS/SECRET.TXT or use backslash separators instead of forward slashes. This bypass mechanism operates within the scope of the user's existing authentication and authorization permissions, making it particularly dangerous as it leverages legitimate access rights to achieve unauthorized file access.
The vulnerability can be classified under CWE-22 Path Traversal and aligns with ATT&CK technique T1078 Valid Accounts for maintaining persistent access. It represents a critical weakness in the application's input validation and path handling mechanisms, allowing attackers to circumvent security controls through manipulation of path representation rather than exploiting authentication bypasses or other more traditional attack vectors. The issue is particularly concerning in environments where filebrowser serves as a primary file management interface and administrators rely on granular access control policies to protect sensitive data.
The recommended mitigations include implementing proper path canonicalization before any access rule evaluation, ensuring that all incoming paths are normalized to their standard form regardless of case or separator variations. Organizations should upgrade to filebrowser version 26321 or later where this vulnerability has been addressed through proper path normalization routines. Additionally, administrators should implement additional monitoring for unusual path patterns and consider implementing more robust access control mechanisms beyond simple path-based rules. Security teams should also review existing access policies to ensure they account for potential path variant attacks and regularly audit file access logs for suspicious activities that might indicate exploitation attempts.