CVE-2026-54910: FileBrowser Quantum Path Traversal Vulnerability Allows Authenticated Users to Read Arbitrary Files

Executive Intelligence Brief

A critical path traversal vulnerability, CVE-2026-54910, has been discovered in FileBrowser Quantum's subtitle handler. This flaw allows any authenticated user to read arbitrary files on the host filesystem, including sensitive files such as /etc/passwd, SSH keys, and database credentials. The vulnerability is caused by the lack of sanitization in the `path` and `name` parameters used in filesystem operations. Immediate patching is recommended to prevent potential exploitation.

Threat Overview

FileBrowser Quantum is a popular file management platform used for managing and sharing files. The subtitle handler endpoint (`GET /api/media/subtitles`) is vulnerable to a path traversal attack, which allows an attacker to escape the storage root and access any directory on the host. This vulnerability has a significant impact, as it can be exploited by any authenticated user, regardless of role or permissions.

Technical Deep Dive

Vulnerability Classification

The vulnerability is classified as a path traversal vulnerability (CWE-22). This type of vulnerability occurs when an application does not properly sanitize user input, allowing an attacker to manipulate file paths and access sensitive files.

Root Cause Analysis

The root cause of the vulnerability is the lack of sanitization in the `path` and `name` parameters used in filesystem operations. The `path` parameter is passed directly to `idx.GetRealPath()` without calling `SanitizeUserPath()`, allowing an attacker to escape the storage root and set `parentDir` to any directory on the host. The `name` parameter is joined with `parentDir` via `filepath.Join(parentDir, name)` without stripping directory components, allowing traversal relative to any resolved `parentDir`.

Attack Vector & Chain

The attack vector involves exploiting the subtitle handler endpoint (`GET /api/media/subtitles`) with a crafted `path` and `name` parameter. An attacker can use either parameter to traverse the filesystem and access sensitive files. The attack chain involves: 1. Initial access: The attacker must be authenticated to the FileBrowser Quantum platform. 2. Exploitation: The attacker sends a crafted request to the subtitle handler endpoint with a malicious `path` and `name` parameter. 3. Impact realization: The attacker can read arbitrary files on the host filesystem, including sensitive files.

Exploitation Scenario Walkthrough

**Scenario: Path Traversal via Subtitle Handler Endpoint** 1. Reconnaissance: The attacker discovers the vulnerable endpoint (`GET /api/media/subtitles`) and determines that it requires authentication. 2. Weaponization: The attacker crafts a request with a malicious `path` and `name` parameter to traverse the filesystem. 3. Delivery & Exploitation: The attacker sends the crafted request to the subtitle handler endpoint, exploiting the path traversal vulnerability. 4. Post-Exploitation: The attacker reads arbitrary files on the host filesystem, including sensitive files such as /etc/passwd, SSH keys, and database credentials. 5. Impact Realization: The attacker can use the sensitive information to escalate privileges, access restricted areas of the system, or compromise the system further.

Exploitation in the Wild

There is no evidence of active exploitation in the wild. However, the vulnerability is considered high-severity and should be patched immediately to prevent potential exploitation.

Impact Analysis

Direct Impact

The vulnerability allows any authenticated user to read arbitrary files on the host filesystem, including sensitive files such as /etc/passwd, SSH keys, and database credentials. This can lead to: * Arbitrary file read * Credential exposure * Privilege escalation

Downstream & Cascading Effects

The vulnerability can have downstream effects, including: * Supply chain risk: If FileBrowser Quantum is used in a supply chain, an attacker could exploit the vulnerability to access sensitive information. * Regulatory implications: Depending on the jurisdiction, the exposure of sensitive information could have regulatory implications.

Affected Products & Versions

The vulnerability affects FileBrowser Quantum. The fix involves applying `SanitizeUserPath()` to the `path` parameter and `filepath.Base()` to the `name` parameter.

Detection & Threat Hunting

Indicators of Compromise

There are no known indicators of compromise. However, monitoring for suspicious activity on the FileBrowser Quantum platform and the host filesystem can help detect potential exploitation.

Detection Rules & Signatures

Detection rules can be created to monitor for suspicious activity on the FileBrowser Quantum platform and the host filesystem. For example: * Monitor for requests to the subtitle handler endpoint (`GET /api/media/subtitles`) with suspicious `path` and `name` parameters. * Monitor for file access patterns that indicate potential path traversal.

Threat Hunting Queries

Threat hunting queries can be created to identify potential exploitation. For example: * Search for requests to the subtitle handler endpoint (`GET /api/media/subtitles`) with suspicious `path` and `name` parameters. * Search for file access patterns that indicate potential path traversal.

Remediation & Hardening

Immediate Actions (0-24 hours)

* Apply the fix: Apply `SanitizeUserPath()` to the `path` parameter and `filepath.Base()` to the `name` parameter. * Monitor for suspicious activity: Monitor for requests to the subtitle handler endpoint (`GET /api/media/subtitles`) with suspicious `path` and `name` parameters.

Short-Term Hardening (1-7 days)

* Implement additional security controls: Implement additional security controls, such as network segmentation, WAF rules, and access restrictions. * Monitor for suspicious activity: Monitor for requests to the subtitle handler endpoint (`GET /api/media/subtitles`) with suspicious `path` and `name` parameters.

Strategic Recommendations

* Implement secure coding practices: Implement secure coding practices, such as input validation and sanitization, to prevent similar vulnerabilities. * Conduct regular security audits: Conduct regular security audits to identify and address potential vulnerabilities.

Analyst Assessment

The vulnerability is considered high-severity and should be patched immediately to prevent potential exploitation. The likelihood of exploitation is moderate, given the authentication requirement and the complexity of the attack vector. However, the impact of exploitation is significant, as it can lead to arbitrary file read, credential exposure, and privilege escalation.