CVE-2023-39611

Executive Summary

CVE-2023-39611 is a path traversal vulnerability in Software FX Chart FX 7 (version 7.0.4962.20829). An attacker can send crafted web requests to enumerate and read arbitrary files from the local filesystem of the server hosting the Chart FX 7 application. This vulnerability is currently unpatched, with no official fix available from the vendor. The EPSS score is 0.0%, indicating low exploitation activity in the wild, but the risk is significant due to the potential for sensitive data exposure.

Supply Chain & Package Security

This vulnerability affects a proprietary software component (Chart FX 7) and is not related to open-source package ecosystems (NPM, PyPI, Go, Ruby). No supply chain attack vector is identified.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, but based on the vulnerability description, a reasonable assessment would be:

• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: None (PR:N)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: High (C:H)
• Integrity Impact: None (I:N)
• Availability Impact: None (A:N)
• Base Score: 7.5 (High)

Threat Level: High – Unauthenticated remote file read can lead to exposure of configuration files, credentials, and sensitive business data.

Deep Dive & Mechanics

The vulnerability resides in the web interface of Chart FX 7, which processes user-supplied input without proper sanitization. By manipulating parameters in HTTP requests (likely file paths or resource identifiers), an attacker can traverse directories outside the intended web root. For example, a request like:

GET /ChartFX/../../windows/win.ini HTTP/1.1

could return the contents of win.ini if the application does not validate the path.

The root cause is a lack of input validation and insufficient path canonicalization. The application likely uses a function like File.ReadAllText(userInput) without checking for .. sequences.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual C#):

public string GetFileContent(string fileName)
{
    string basePath = "C:\\Program Files\\ChartFX\\Resources\\";
    string fullPath = basePath + fileName;
    return File.ReadAllText(fullPath);
}

Patched Code (Conceptual):

public string GetFileContent(string fileName)
{
    string basePath = "C:\\Program Files\\ChartFX\\Resources\\";
    string fullPath = Path.GetFullPath(Path.Combine(basePath, fileName));
    if (!fullPath.StartsWith(basePath))
    {
        throw new SecurityException("Invalid path.");
    }
    return File.ReadAllText(fullPath);
}

The patched version uses Path.GetFullPath to resolve .. sequences and then verifies that the resolved path starts with the allowed base directory.

Exploitation & Lab Setup

Red Team

1. Identify Target: Scan for Chart FX 7 endpoints (e.g., /ChartFX/, /fxchart/).
2. Craft Request: Use a tool like curl or Burp Suite to send a path traversal payload:

   curl "http://target.com/ChartFX/../../windows/win.ini"
   

3. Enumerate Files: Try common files:
   • /etc/passwd (Linux)
   • ../../../../etc/passwd
   • ../../../../Windows/System32/drivers/etc/hosts
4. Automate: Use a script to brute-force file paths.

Blue Team

1. Monitor Logs: Look for HTTP requests containing ../ or ..%2f patterns.
2. Deploy WAF Rules: Block requests with path traversal sequences.
3. Harden Application: Restrict file system access via application pool identity (IIS) or container permissions.
4. Network Segmentation: Isolate the Chart FX server from sensitive data stores.

Indicators of Compromise (IOCs)

• Network: HTTP requests with ../ or ..%2f in the URI path.
• Logs: Web server logs showing 200 responses to path traversal patterns.
• File System: Unexpected access to files outside the web root (e.g., win.ini, passwd).
• Process: Chart FX process reading files from system directories.

Detection Engineering

YARA Rule

Sigma Rule

Suricata Rule

Remediation & Mitigation

Since no official patch is available, the following mitigations are recommended:

1. Input Validation: Implement strict allowlisting of allowed file paths.
2. Web Application Firewall (WAF): Deploy rules to block path traversal patterns.
3. Least Privilege: Run the Chart FX application with minimal file system permissions.
4. Network Controls: Restrict access to the Chart FX interface to trusted IPs only.
5. Monitor: Continuously monitor for exploitation attempts using the provided detection rules.
6. Vendor Contact: Reach out to Software FX for a security update.

Valters IT
DevSecOps & Cyber Threat Intelligence