CVE-2026-4620: NEC Aterm WX3600HP Firmware RCE Flaw

CVE-2026-4620 Overview

CVE-2026-4620 is an OS command injection vulnerability [CWE-78] affecting NEC Platforms Aterm Series wireless routers. The flaw allows an authenticated attacker with high privileges to execute arbitrary operating system commands over the network. Successful exploitation impacts the confidentiality, integrity, and availability of the affected device. NEC published security advisory NV26-001 documenting the issue and providing remediation guidance for impacted models.

Critical Impact

Attackers who gain administrative access to an Aterm router can execute arbitrary OS commands, gaining full control over the device and pivoting deeper into the network.

Affected Products

• NEC Aterm WX3600HP (hardware and firmware)
• NEC Aterm WX1500HP (hardware and firmware)
• Refer to NEC Security Advisory NV26-001 for specific firmware versions

Discovery Timeline

• 2026-03-27 - CVE-2026-4620 published to NVD
• 2026-04-20 - Last updated in NVD database

Technical Details for CVE-2026-4620

Vulnerability Analysis

The vulnerability is classified under [CWE-78], Improper Neutralization of Special Elements used in an OS Command. Affected NEC Aterm WX3600HP and WX1500HP routers fail to properly sanitize input passed to underlying operating system command interpreters. An attacker who is authenticated with administrative privileges can inject shell metacharacters into a vulnerable parameter. The injected commands execute in the context of the router firmware, typically with elevated privileges on the embedded Linux system.

Successful exploitation allows full compromise of the router, including persistent firmware modification, traffic interception, credential theft, and lateral movement into protected internal networks. The CVSS 4.0 vector indicates network reach with user interaction and high privileges required, lowering the practical attack surface but not eliminating it for environments where router credentials are weak or reused.

Root Cause

The root cause is insufficient input validation in management interface handlers that pass user-controlled values to OS command execution functions. Shell metacharacters such as ;, |, &, and backticks are not stripped or escaped before command construction.

Attack Vector

The attack vector is network-based. An attacker must first authenticate to the router's management interface with high-privilege credentials and induce user interaction. Once authenticated, the attacker submits a crafted request containing injected command syntax to the vulnerable endpoint. NEC has not published a public proof-of-concept, and no exploit code is currently available. See NEC Security Advisory NV26-001 for vendor technical details.

Detection Methods for CVE-2026-4620

Indicators of Compromise

• Unexpected outbound connections originating from the router management plane to unknown hosts.
• Unauthorized changes to router configuration, DNS settings, or firewall rules.
• New or unknown administrator sessions in router access logs, particularly from external IP addresses.
• Unusual processes or persistence artifacts in firmware diagnostic output.

Detection Strategies

• Monitor HTTP/HTTPS requests to the Aterm management interface for shell metacharacters such as ;, |, &, $(), or backticks in parameter values.
• Inspect router system logs for command execution anomalies and unexpected service restarts.
• Correlate authentication events with subsequent configuration changes to identify suspicious administrative sessions.

Monitoring Recommendations

• Forward router syslog data to a centralized log analytics platform for retention and correlation.
• Alert on administrative logins from non-management network segments or unexpected geolocations.
• Track firmware version drift across the device fleet to confirm patch deployment status.

How to Mitigate CVE-2026-4620

Immediate Actions Required

• Apply the firmware updates published by NEC for the Aterm WX3600HP and WX1500HP models as directed in advisory NV26-001.
• Restrict access to the router management interface to trusted internal hosts and disable remote WAN-side administration.
• Rotate all administrator credentials and enforce strong, unique passwords for router accounts.
• Audit router configuration for unauthorized changes introduced prior to patching.

Patch Information

NEC has released firmware updates addressing CVE-2026-4620. Refer to NEC Security Advisory NV26-001 for the specific fixed firmware versions and download instructions for each affected Aterm model.

Workarounds

• Disable the router's remote management feature if firmware updates cannot be applied immediately.
• Place the router management interface behind a VLAN or ACL that limits access to authorized administrator workstations.
• Monitor administrative authentication attempts and lock out accounts after repeated failures.

# Configuration example: restrict management access at the network layer
# Example ACL on an upstream firewall - replace 192.0.2.10 with your admin host
iptables -A FORWARD -p tcp -d <router_ip> --dport 443 -s 192.0.2.10 -j ACCEPT
iptables -A FORWARD -p tcp -d <router_ip> --dport 443 -j DROP