CVE-2026-90930 in File Browser
Summary
by MITRE • 09/14/2026
File Browser through 2.63.23 applies path rules to the requested lexical path but resolves symbolic links without reapplying rules to the target, allowing authenticated users to bypass deny rules. Attackers can read and overwrite rule-denied files by accessing them through in-scope symbolic link aliases that resolve to denied paths.
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Analysis
by VulDB Data Team • 09/14/2026
The vulnerability identified in File Browser versions up to 2.63.23 represents a critical security flaw rooted in improper handling of path resolution, specifically concerning the interaction between lexical path validation and symbolic link dereferencing. This issue stems from a fundamental architectural oversight where the application enforces access control policies based on the initial user-supplied input string rather than the final resolved file system location. When an authenticated user requests access to a resource, the software correctly applies its deny rules against the provided path syntax. However, if that lexical path contains symbolic links pointing outside the permitted directory scope or toward restricted files, the application fails to re-evaluate those target paths against the same security policies after resolution. This creates a classic bypass mechanism where the initial validation step is rendered ineffective by subsequent operating system-level link translation operations that occur without corresponding security checks.
From a technical perspective, this flaw aligns with CWE-22 Improper Limitation of a Pathname to a Restricted Directory and CWE-59 Improper Link Resolution Before File Access. The core issue lies in the sequence of operations within the request handling logic. Typically, secure implementations must canonicalize or resolve all symbolic links before performing any access control decisions. In this vulnerable implementation, the security middleware inspects the raw input for forbidden patterns or paths and blocks them if they match deny rules. Yet, because the actual file read or write operation occurs after the operating system resolves the symbolic link to its absolute target path, the application inadvertently grants access to resources that were explicitly prohibited by the initial lexical check. This discrepancy allows an attacker who possesses valid authentication credentials to circumvent directory traversal protections and file access restrictions simply by crafting a request where the visible path is allowed but the underlying symlink points to a restricted location.
The operational impact of this vulnerability is significant for any deployment relying on File Browser to manage sensitive data or enforce strict isolation between user directories. An authenticated attacker can exploit this flaw to read confidential files that reside outside their designated workspace, potentially exposing proprietary information, personal identifiable data, or system configuration details. Furthermore, the ability to overwrite rule-denied files introduces a risk of integrity compromise and potential remote code execution if critical binaries or scripts are targeted. This undermines the principle of least privilege by allowing users to interact with resources they should not have access to based on their assigned roles or permissions. The severity is heightened in multi-tenant environments where such bypasses could lead to cross-user data leakage, violating compliance requirements for data isolation and confidentiality.
Mitigation strategies must focus on ensuring that all path resolution occurs prior to security policy evaluation. Developers should update the application logic to resolve symbolic links using canonicalization functions before applying deny rules or checking access permissions. This ensures that both the requested path and its ultimate target are validated against the same set of restrictions, eliminating the possibility of bypassing controls through link indirection. Additionally, implementing strict chroot jails or containerized environments with restricted mount points can provide a defense-in-depth layer by limiting the operating system's ability to resolve links outside designated boundaries at all levels. Organizations running affected versions should immediately apply vendor-provided patches that address this path resolution logic error and review their access control configurations to ensure no sensitive files are accessible via alternative paths within the file system hierarchy. This vulnerability is categorized under ATT&CK technique T1083 File and Directory Discovery, as it enables an attacker to enumerate and access restricted resources through indirect means rather than direct brute-force or scanning methods.