CVE-2025-69820: Beam beta9 Path Traversal Vulnerability

CVE-2025-69820 Overview

A Directory Traversal vulnerability has been identified in Beam beta9 v.0.1.552. This security flaw allows a remote attacker to obtain sensitive information by exploiting the joinCleanPath function. Directory traversal vulnerabilities, also known as path traversal attacks (CWE-22), enable attackers to access files and directories stored outside the intended directory hierarchy by manipulating file path references.

Critical Impact

Remote attackers can leverage this vulnerability to read arbitrary files from the system, potentially exposing sensitive configuration data, credentials, source code, or other confidential information stored on the affected server.

Affected Products

• Beam beta9 v.0.1.552

Discovery Timeline

• 2026-01-22 - CVE CVE-2025-69820 published to NVD
• 2026-01-22 - Last updated in NVD database

Technical Details for CVE-2025-69820

Vulnerability Analysis

This directory traversal vulnerability exists within the joinCleanPath function in Beam beta9. The function fails to properly sanitize user-supplied input containing path traversal sequences such as ../ (dot-dot-slash), allowing attackers to escape the intended directory and access arbitrary files on the system.

The vulnerability requires local access with high privileges to exploit. While the scope is unchanged, successful exploitation can result in high confidentiality and integrity impacts, though availability is not affected. This indicates that attackers could both read sensitive files and potentially modify data on the affected system.

Root Cause

The root cause of this vulnerability lies in insufficient input validation within the joinCleanPath function. The function does not adequately sanitize or validate file path inputs, failing to remove or neutralize directory traversal sequences before constructing the final file path. This allows specially crafted input containing sequences like ../ to traverse up the directory structure and access files outside the intended scope.

Attack Vector

The attack vector is local, requiring the attacker to have existing access to the system with high-level privileges. Despite these prerequisites, successful exploitation allows an attacker to craft malicious requests containing directory traversal sequences targeting the joinCleanPath function. By including patterns such as ../../../etc/passwd or similar path manipulations, the attacker can force the application to access and return the contents of arbitrary files from the filesystem.

The vulnerability mechanism involves path manipulation through the vulnerable joinCleanPath function. Attackers supply input containing traversal sequences that bypass intended directory restrictions. For detailed technical analysis and proof-of-concept information, refer to the GitHub CVE PoC Repository.

Detection Methods for CVE-2025-69820

Indicators of Compromise

• File access logs showing requests containing ../ or encoded variants (%2e%2e%2f, ..%2f) in path parameters
• Unexpected access attempts to sensitive system files such as /etc/passwd, configuration files, or application source code
• Error messages or log entries indicating attempts to access files outside the web root or application directory

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block path traversal patterns in HTTP requests
• Monitor application logs for anomalous file access patterns or repeated failed file read attempts
• Deploy file integrity monitoring to detect unauthorized access to sensitive configuration files

Monitoring Recommendations

• Enable verbose logging for the Beam application to capture all file access operations through the joinCleanPath function
• Configure SIEM alerts for path traversal attack patterns across web server and application logs
• Regularly audit file access permissions and monitor for unauthorized changes to sensitive files

How to Mitigate CVE-2025-69820

Immediate Actions Required

• Upgrade Beam to a patched version when available from the vendor
• Implement input validation to reject any file path containing directory traversal sequences
• Restrict application permissions using the principle of least privilege to limit potential damage from exploitation
• Consider deploying a web application firewall to filter malicious requests while awaiting a patch

Patch Information

A security advisory has been issued regarding this vulnerability. Users should monitor the GitHub Security Advisory for patch availability and update instructions. Upgrade to the latest version of Beam once a security patch has been released.

Workarounds

• Implement server-side input validation to reject any path containing .., ./, or URL-encoded equivalents before passing to joinCleanPath
• Configure file system permissions to restrict the application's read access to only necessary directories
• Deploy network segmentation to limit the exposure of systems running vulnerable Beam instances
• Use a reverse proxy with path normalization capabilities to sanitize incoming requests

# Example configuration for input validation at web server level (nginx)
# Block requests containing path traversal sequences
location / {
    if ($request_uri ~* "\.\.") {
        return 403;
    }
    # Additional security headers
    add_header X-Content-Type-Options nosniff;
    add_header X-Frame-Options DENY;
}