CVE-2026-54089 in File Browser
Summary
by MITRE • 06/25/2026
File Browser is a file managing interface for uploading, deleting, previewing, renaming, and editing files within a specified directory. Starting with 2.0.0-rc.1, when FileBrowser is configured with proxy authentication (auth.method=proxy), any unauthenticated attacker who can reach the server directly can impersonate any user - including admin - by sending a single forged HTTP header. No credentials are required. Additionally, specifying a non-existent username causes the server to automatically create a new user account, providing an account creation primitive with no authorization. This is an already known issue that has been documented in the documentation for several years, but has not been documented as a vulnerability before.
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Analysis
by VulDB Data Team • 06/26/2026
The vulnerability described represents a critical authentication bypass flaw in File Browser versions 2.0.0-rc.1 and later, specifically when configured with proxy authentication mode. This issue stems from improper handling of HTTP headers that are typically used to convey user identity information in reverse proxy setups. When the system operates in auth.method=proxy mode, it relies on specific HTTP headers such as X-Forwarded-User or similar mechanisms to determine user identities. The flaw occurs because File Browser fails to properly validate or sanitize these headers, allowing any unauthenticated attacker who can directly reach the server to forge user identities by simply including a malicious value in the appropriate HTTP header.
The technical implementation of this vulnerability exploits the trust model inherent in proxy authentication configurations where the application assumes that forwarded headers contain legitimate user information without proper verification. This creates a privilege escalation vector where an attacker can impersonate any user account, including administrative accounts, by manipulating HTTP request headers. The system's behavior of automatically creating new user accounts when presented with non-existent usernames further compounds the security issue by providing an account creation primitive that operates without any authorization checks or validation mechanisms. This automatic account creation functionality essentially provides attackers with a means to establish persistent access points within the system.
The operational impact of this vulnerability is severe as it completely undermines the authentication and authorization mechanisms of File Browser. An attacker can not only access files and directories but can also assume administrative privileges without any credentials, making this a critical security flaw that affects all users of the affected versions. The vulnerability's persistence across multiple years without being documented as a formal security issue highlights a gap in vulnerability disclosure practices within the project ecosystem. This type of authentication bypass vulnerability would typically be classified under CWE-287 which deals with improper handling of authentication tokens, and could be categorized under ATT&CK technique T1078 for Valid Accounts and T1566 for Phishing as attackers could potentially use this to gain unauthorized access to sensitive data.
The mitigation strategies for this vulnerability should include immediate patching of affected versions or implementing strict header validation mechanisms that ensure forwarded user information comes from trusted proxy sources. Organizations using File Browser with proxy authentication should also implement additional security controls such as restricting direct server access, validating the source of forwarded headers through IP address verification, and disabling automatic user creation features in production environments. The vulnerability demonstrates the importance of proper input validation and the principle of least privilege in authentication systems, where relying on unverified headers from potentially malicious sources creates dangerous attack vectors that can be exploited without any authentication requirements or authorization checks.