CVE-2025-67487: Static Web Server Path Traversal Flaw

CVE-2025-67487 Overview

Static Web Server (SWS) is a production-ready web server designed for serving static web files and assets. A symlink path traversal vulnerability has been identified in versions 2.40.0 and below that allows attackers to access files or directories outside the intended web root folder. The vulnerability stems from SWS not preventing symbolic links from escaping the web server's root directory, enabling unauthorized file access through crafted URL requests or directory listings.

Critical Impact

Attackers with access to the web server's root directory can create symlinks to access sensitive files outside the designated web root, potentially exposing configuration files, credentials, or other sensitive data on the host system.

Affected Products

• Static Web Server (SWS) versions 2.40.0 and below
• Static-web-server static_web_server (Rust crate)

Discovery Timeline

• 2025-12-09 - CVE CVE-2025-67487 published to NVD
• 2025-12-11 - Last updated in NVD database

Technical Details for CVE-2025-67487

Vulnerability Analysis

This vulnerability is classified under CWE-61 (UNIX Symbolic Link Following) and CWE-59 (Improper Link Resolution Before File Access). The core issue lies in how Static Web Server handles symbolic links within its web root directory. When serving static content, SWS follows symlinks without validating whether the target path remains within the configured web root boundary, creating a path traversal condition.

An attacker who can write files to the web root (either through a separate vulnerability, misconfiguration, or legitimate access) can craft symbolic links pointing to sensitive files elsewhere on the filesystem. These linked files become accessible via HTTP requests or through the directory listing feature, effectively bypassing the web root containment.

Root Cause

The root cause is improper link resolution before file access (CWE-59). Static Web Server fails to implement proper symlink validation that would verify the resolved path remains within the web root boundary. The server follows symbolic links without checking if the ultimate target escapes the designated serving directory, allowing unrestricted filesystem traversal through crafted symlinks.

Attack Vector

The attack vector is network-based, requiring the attacker to either have write access to the web root directory or exploit another vulnerability to create symbolic links. Once a malicious symlink is in place, any remote user can access the linked files through standard HTTP requests.

The exploitation process involves:

1. Gaining write access to the web server's root directory
2. Creating a symbolic link pointing to a target file or directory outside the web root (e.g., /etc/passwd, configuration files, or application data)
3. Accessing the symlink via URL or discovering it through directory listing
4. Retrieving sensitive file contents through the web server's HTTP response

For example, an attacker could create a symlink like ln -s /etc/passwd ./exposed within the web root, making the system password file accessible via HTTP request.

Detection Methods for CVE-2025-67487

Indicators of Compromise

• Presence of symbolic links in the web root directory pointing to locations outside the web root
• Unusual file access patterns in web server logs showing requests for sensitive system paths
• HTTP requests containing path patterns that correspond to system files (e.g., requests returning content matching /etc/passwd format)
• Newly created symlinks in web-accessible directories, especially those created by non-administrative users

Detection Strategies

• Implement file integrity monitoring on the web root directory to detect new symlink creation
• Configure web application firewalls to detect and block requests for known sensitive file patterns
• Review web server access logs for requests that return content inconsistent with expected static assets
• Scan web root directories periodically for symbolic links using find -type l and validate their targets

Monitoring Recommendations

• Enable enhanced logging on Static Web Server to capture all file access requests
• Monitor filesystem events in the web root directory for symlink creation operations
• Set up alerts for any symlink targets that resolve outside the designated web root path
• Implement continuous security scanning of web-accessible directories for unauthorized symlinks

How to Mitigate CVE-2025-67487

Immediate Actions Required

• Upgrade Static Web Server to version 2.40.1 or later immediately
• Audit existing web root directories for any symbolic links and remove unauthorized ones
• Restrict write access to the web root directory to only essential administrative accounts
• Review server logs for any evidence of exploitation or suspicious file access patterns

Patch Information

The vulnerability is fixed in Static Web Server version 2.40.1. The patch implements proper symlink validation to prevent links from escaping the web root directory. The fix is available in commit 308f0d26ceb9c2c8bd219315d0f53914763357f2. For detailed information, refer to the GitHub Security Advisory GHSA-459f-x8vq-xjjm and the commit containing the fix.

Workarounds

• Remove or disable directory listing functionality if not required to reduce attack surface
• Implement filesystem-level restrictions using mount options like nosymfollow where supported
• Use a reverse proxy in front of Static Web Server that validates and sanitizes request paths
• Apply strict file permissions and ownership on the web root to prevent unauthorized symlink creation
• Consider containerizing the web server with read-only filesystem mounts for the web root

# Find and audit symbolic links in web root directory
find /path/to/webroot -type l -exec ls -la {} \;

# Identify symlinks pointing outside web root
find /path/to/webroot -type l -exec readlink -f {} \; | grep -v "^/path/to/webroot"

# Remove unauthorized symlinks (review before executing)
# find /path/to/webroot -type l -delete