CVE-2026-4840: Netcore Power 15AX RCE Vulnerability

CVE-2026-4840 Overview

CVE-2026-4840 is an operating system command injection vulnerability affecting Netcore Power 15AX routers up to firmware version 3.0.0.6938. The flaw resides in the setTools function of the /bin/netis.cgi binary, part of the Diagnostic Tool Interface. Attackers can manipulate the IpAddr argument to inject arbitrary operating system commands. The vulnerability is exploitable remotely over the network and a public proof-of-concept has been released. The vendor was contacted prior to public disclosure but did not respond. The weakness is tracked as CWE-77, Improper Neutralization of Special Elements used in a Command.

Critical Impact
Remote attackers with low privileges can execute arbitrary operating system commands on affected Netcore Power 15AX devices, leading to full device compromise.

Affected Products

Netcore Power 15AX firmware versions up to 3.0.0.6938
Component: Diagnostic Tool Interface (/bin/netis.cgi)
Vulnerable function: setTools

Discovery Timeline

2026-03-26 - CVE-2026-4840 published to NVD
2026-04-24 - Last updated in NVD database

Technical Details for CVE-2026-4840

Vulnerability Analysis

The vulnerability resides in the setTools function exposed by the /bin/netis.cgi binary on Netcore Power 15AX devices. This CGI endpoint handles diagnostic operations such as connectivity tests. The IpAddr parameter, which should accept a target IP address, is concatenated into a shell command without sanitization. Attackers supply shell metacharacters in IpAddr to break out of the intended command context and execute arbitrary operating system commands. Successful exploitation grants the attacker code execution under the privilege level of the CGI process, typically root on embedded router firmware. A public proof-of-concept exploit increases the likelihood of opportunistic scanning and exploitation.

Root Cause

The root cause is improper neutralization of special elements used in an OS command [CWE-77]. The setTools handler passes user-controlled input directly to a shell interpreter without input validation, escaping, or use of safe execution primitives such as execve with argument arrays. Shell metacharacters including ;, |, &, and backticks are interpreted by the underlying shell.

Attack Vector

Exploitation requires network access to the device's management interface and a low-privilege authenticated context. An attacker sends a crafted HTTP request to the diagnostic endpoint with a malicious IpAddr value containing shell metacharacters followed by attacker-chosen commands. The router executes the injected command. Routers exposed to untrusted networks or with weak default credentials are at elevated risk. Refer to the GitHub PoC Repository and the VulDB CVE Analysis for technical details.

Detection Methods for CVE-2026-4840

Indicators of Compromise

HTTP POST or GET requests to /bin/netis.cgi containing shell metacharacters such as ;, |, &, or backticks in the IpAddr parameter.
Unexpected outbound connections from the router to attacker-controlled infrastructure, often indicating reverse shell or payload retrieval.
New or modified processes, cron entries, or startup scripts on the device that do not correspond to vendor firmware.

Detection Strategies

Inspect web server and reverse proxy logs in front of router management interfaces for requests targeting netis.cgi with non-IP characters in IpAddr.
Deploy network IDS signatures that flag command injection patterns in HTTP parameters destined for the router management interface.
Monitor DNS and NetFlow data for anomalous traffic originating from the router's IP address.

Monitoring Recommendations

Restrict management plane access to a dedicated VLAN and log all administrative HTTP traffic.
Forward router syslog, authentication logs, and firewall flow records to a centralized analytics platform for correlation.
Alert on configuration changes, firmware version drift, and unexpected privileged process execution on network devices.

How to Mitigate CVE-2026-4840

Immediate Actions Required

Remove Netcore Power 15AX devices from untrusted networks and disable remote WAN-side management until a fix is available.
Rotate administrative credentials and disable any unused accounts on affected devices.
Apply network segmentation to isolate management interfaces behind a firewall or VPN.

Patch Information

No vendor patch is currently referenced in the available advisories. The vendor was contacted prior to public disclosure but did not respond. Organizations should track vendor communications and consider replacement with a supported device if a fix is not released. Refer to the VulDB entry for ongoing updates.

Workarounds

Block external access to the router's HTTP management interface using upstream firewall rules.
Disable the diagnostic tool feature in the device web interface if the configuration option exists.
Enforce administrative access only from a trusted management workstation over a VPN or jump host.

bash

# Example upstream firewall rule to block external access to the management interface
# Replace ROUTER_IP and ADMIN_SUBNET with environment-specific values
iptables -A FORWARD -p tcp -d ROUTER_IP --dport 80 -s ADMIN_SUBNET -j ACCEPT
iptables -A FORWARD -p tcp -d ROUTER_IP --dport 80 -j DROP
iptables -A FORWARD -p tcp -d ROUTER_IP --dport 443 -s ADMIN_SUBNET -j ACCEPT
iptables -A FORWARD -p tcp -d ROUTER_IP --dport 443 -j DROP