CVE-2025-27932

Executive Summary

CVE-2025-27932 is a critical path traversal vulnerability in the USB storage file-sharing function of the HGW-BL1500HM router, affecting firmware versions 002.002.003 and earlier. The flaw allows an unauthenticated attacker to delete arbitrary files on the device or cause a denial of service (DoS) by exploiting improper pathname limitation during file deletion. With a CVSS score of 8.1, this vulnerability poses a high risk to device integrity and availability. No public exploit code or patch is currently available, but the attack surface is exposed via the device’s network interface.

Note: This vulnerability is specific to the HGW-BL1500HM router hardware and firmware. It is not related to any WordPress plugin or component.

Supply Chain & Package Security

This vulnerability is not associated with any open-source package ecosystem (NPM, PyPI, Go, Ruby). The affected component is proprietary firmware for a consumer router.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
• Base Score: 8.1 (High)
• Attack Vector: Network (AV:N) – Exploitable remotely.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – Impact confined to the device.
• Confidentiality Impact: None (C:N) – No data exposure.
• Integrity Impact: High (I:H) – Arbitrary file deletion possible.
• Availability Impact: High (A:H) – DoS condition achievable.

Threat Level: High. The vulnerability is remotely exploitable without authentication, enabling attackers to delete critical system files or disrupt device operation.

Deep Dive & Mechanics

The vulnerability resides in the USB storage file-sharing function of the HGW-BL1500HM router. This function allows users to share files from a connected USB drive over the network. The file deletion process fails to properly sanitize user-supplied pathnames, allowing an attacker to traverse directories outside the intended USB storage directory.

Root Cause: The application does not validate or restrict pathnames to the designated USB storage directory. By injecting path traversal sequences (e.g., ../), an attacker can reference arbitrary files on the device’s filesystem.

Attack Vector: An unauthenticated attacker sends a crafted HTTP request to the file deletion endpoint, specifying a path like ../../etc/passwd or ../../bin/sh. The server processes the request without proper validation, deleting the targeted file.

Impact:

• File Deletion: Critical system files (e.g., configuration files, binaries) can be deleted, leading to device malfunction.
• Denial of Service (DoS): Deleting essential files (e.g., kernel modules, init scripts) can render the device inoperable until manual recovery.

Affected Endpoint: Likely a web interface endpoint such as /cgi-bin/delete_file or /api/delete that accepts a path parameter.

Vulnerable vs. Patched Code

Since no patch is available, the following illustrates the vulnerable code pattern and a hypothetical fix.

Vulnerable Code (Python-like pseudocode):

def delete_file(request):
    file_path = request.GET.get('path')
    # No validation of file_path
    os.remove(file_path)
    return "File deleted"

Patched Code (Hypothetical fix):

import os
import re

USB_BASE_DIR = "/mnt/usb_storage"

def delete_file(request):
    file_path = request.GET.get('path')
    # Sanitize and resolve path
    safe_path = os.path.normpath(os.path.join(USB_BASE_DIR, file_path))
    # Ensure the resolved path is within the base directory
    if not safe_path.startswith(USB_BASE_DIR):
        return "Invalid path", 403
    if not os.path.exists(safe_path):
        return "File not found", 404
    os.remove(safe_path)
    return "File deleted"

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Target device running HGW-BL1500HM firmware 002.002.003 or earlier.
• Network access to the device’s web interface (typically port 80 or 443).

Exploitation Steps:

1. Identify the file deletion endpoint (e.g., via directory brute-forcing or analyzing the web interface).
2. Craft a request to delete a critical file, such as /etc/passwd or a system binary.
3. Use path traversal sequences to escape the USB storage directory.

Example Request (using curl):

curl -X POST "http://<target_ip>/cgi-bin/delete_file?path=../../etc/passwd"

Expected Outcome: The device may become unstable or unresponsive after deleting critical files.

Note: No public exploit code is available. The above is a conceptual demonstration.

Blue Team (Defense & Detection)

Detection:

• Monitor HTTP requests for path traversal patterns (e.g., ../, ..\\, %2e%2e%2f).
• Alert on requests to file deletion endpoints with suspicious parameters.
• Use network intrusion detection systems (NIDS) to flag anomalous traffic.

Mitigation:

• Restrict access to the device’s web interface to trusted IPs only.
• Disable the USB file-sharing function if not required.
• Apply input validation and path sanitization at the application layer.

Honeypot Strategy:

• Deploy a decoy HGW-BL1500HM device to capture exploitation attempts.
• Log all requests to the file deletion endpoint for analysis.

Indicators of Compromise (IOCs)

Network IOCs:

• HTTP requests containing path traversal sequences in the path parameter (e.g., ../, ..\\, %2e%2e%2f).
• Requests to endpoints like /cgi-bin/delete_file, /api/delete, or similar.
• Unusual outbound traffic from the device after exploitation (e.g., DNS queries for C2 domains).

File System IOCs:

• Missing critical system files (e.g., /etc/passwd, /bin/sh, /sbin/init).
• Unexpected file deletions in system directories.
• Presence of backup files or scripts created by the attacker.

Log IOCs:

• Web server logs showing 200 responses to file deletion requests with path traversal.
• System logs indicating file deletion errors or missing files.

Detection Engineering

YARA Rule

rule CVE_2025_27932_Path_Traversal {
    meta:
        description = "Detects path traversal attempts targeting HGW-BL1500HM file deletion"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-27932"
    strings:
        $path_traversal1 = "../"
        $path_traversal2 = "..\\"
        $path_traversal3 = "%2e%2e%2f"
        $path_traversal4 = "%2e%2e%5c"
        $endpoint = "/cgi-bin/delete_file"
    condition:
        any of ($path_traversal*) and $endpoint
}

Sigma Rule

title: CVE-2025-27932 Path Traversal in HGW-BL1500HM
id: 8a3f7c2e-5d1b-4a9f-8c6e-2b3d1f0a9e8c
status: experimental
description: Detects path traversal attempts in HTTP requests to HGW-BL1500HM file deletion endpoint
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains:
            - '../'
            - '..\\'
            - '%2e%2e%2f'
            - '%2e%2e%5c'
        cs-uri-stem|contains: '/cgi-bin/delete_file'
    condition: selection
falsepositives:
    - Legitimate use of path traversal in other contexts (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-27932 Path Traversal in HGW-BL1500HM"; flow:to_server; content:"POST"; http_method; content:"/cgi-bin/delete_file"; http_uri; content:"../"; http_uri; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable USB File Sharing: If not required, disable the USB file-sharing function via the device’s web interface.
2. Restrict Network Access: Limit access to the device’s web interface to trusted IPs using firewall rules.
3. Monitor Logs: Enable logging and monitor for suspicious file deletion requests.

Long-Term Fix:

• Vendor Patch: Await an official firmware update from the vendor that implements proper path validation.
• Workaround: If patching is not possible, consider replacing the device with a more secure alternative.

Compensating Controls:

• Deploy a web application firewall (WAF) to block path traversal patterns.
• Use network segmentation to isolate the device from critical systems.

Valters IT Signature

Report generated by Valters IT DevSecOps Intelligence Unit