FileBrowser Quantum is a self-hosted, web-based file management system that allows users to share files with password protection. However, in versions prior to 1.1.3-stable and between 1.2.0-beta and 1.2.6-beta, a critical vulnerability (CVE-2026-27611) exists where the API returns a direct download URL within the share details. This URL can be accessed by anyone possessing the share link, bypassing the password protection entirely. The root cause is an exposure of sensitive information (CWE-200) combined with inadequate authentication and authorization controls (CWE-287 and CWE-288). The vulnerability enables unauthorized actors to download files without any authentication or user interaction, posing a serious confidentiality risk. The CVSS 4.0 score of 7.1 reflects the network attack vector, low attack complexity, no privileges or authentication required, but user interaction is needed (accessing the share link). The vulnerability affects all users sharing password-protected files on vulnerable versions, potentially exposing sensitive or confidential data. Fixed versions 1.1.3-stable and 1.2.6-beta address this by removing the direct download link from the share details or enforcing proper access controls. No public exploits have been reported yet, but the vulnerability's nature makes it a prime target for attackers once discovered.

The primary impact of CVE-2026-27611 is the unauthorized disclosure of sensitive files shared via FileBrowser Quantum. Organizations relying on this software for internal or external file sharing risk exposing confidential data, intellectual property, or personally identifiable information (PII) to unauthorized parties. This can lead to data breaches, regulatory non-compliance, reputational damage, and potential financial losses. Since the vulnerability allows bypassing password protection without authentication, attackers only need to obtain or guess the share link, which may be distributed or leaked inadvertently. The scope includes any organization using affected versions for file sharing, especially those sharing sensitive or regulated data. The vulnerability undermines trust in the file sharing system and may disrupt business operations if sensitive files are leaked. Although no exploits are known in the wild, the ease of exploitation and high confidentiality impact make this a critical concern for organizations worldwide.

To mitigate CVE-2026-27611, organizations should immediately upgrade FileBrowser Quantum to version 1.1.3-stable or 1.2.6-beta or later, where the vulnerability is fixed. Until upgrades are applied, administrators should avoid sharing password-protected files using vulnerable versions or disable sharing features if possible. Review and audit existing shared links to identify any that may expose sensitive data and revoke or regenerate them. Implement network-level access controls to restrict access to the FileBrowser instance to trusted users or IP ranges. Monitor logs for unusual access patterns to shared files. Educate users on secure sharing practices and the risks of link sharing. Additionally, consider implementing multi-factor authentication and enhanced access control policies around file sharing services. Regularly check for updates and security advisories from the vendor to stay informed about new vulnerabilities or patches.