CVE-2026-82762: Contec FX Series OS Command Injection RCE

CVE-2026-82762 Overview

CVE-2026-82762 is an OS command injection vulnerability [CWE-78] affecting Contec FX5000, FX4000, and FX3000 series devices. The flaw stems from improper neutralization of special elements passed to operating system commands. An authenticated attacker who can log in to the product can execute arbitrary OS commands on the underlying system. Contec published a security information document alongside JVN advisory JVNVU99009004 confirming the issue.

These Contec FX-series products are industrial networking devices, and successful exploitation gives an attacker command execution in the device's operating context. This enables lateral movement into operational technology (OT) environments and disruption of connected assets.

Critical Impact

Authenticated attackers can execute arbitrary OS commands on affected Contec FX5000, FX4000, and FX3000 devices, compromising confidentiality, integrity, and availability of the underlying system.

Affected Products

• Contec FX5000 series
• Contec FX4000 series
• Contec FX3000 series

Discovery Timeline

• 2026-09-14 - CVE-2026-82762 published to NVD
• 2026-09-16 - Last updated in NVD database

Technical Details for CVE-2026-82762

Vulnerability Analysis

The vulnerability is classified under [CWE-78] as improper neutralization of special elements used in an OS command. Affected Contec FX-series devices accept input from an authenticated user and pass that input into an operating system command without adequate sanitization. Shell metacharacters such as ;, |, &, backticks, and $() are interpreted by the underlying shell rather than treated as literal data.

Exploitation requires prior authentication, which limits opportunistic attacks. However, the network-reachable attack vector means any attacker with valid low-privilege credentials, including reused or default credentials, can trigger command execution. According to the EPSS forecast dated 2026-09-20, the vulnerability sits in the upper-middle range of exploitation probability among scored CVEs.

Root Cause

The root cause is direct concatenation or unsafe interpolation of user-controlled input into a shell command invocation. Instead of using parameterized command execution APIs or strict allow-list validation, the affected firmware invokes the OS shell with attacker-influenced strings. Any special character with meaning to the shell is executed as part of the command.

Attack Vector

The attack vector is network-based and requires low privileges. An attacker first authenticates to the device management interface, then submits crafted input containing shell metacharacters to a vulnerable endpoint or command handler. The injected payload executes with the privileges of the parent process, which on embedded appliances is frequently root or an equivalently privileged service account. Refer to the JVN Security Advisory JVNVU99009004 and the Contec Security Information Document for vendor-specific technical detail.

Detection Methods for CVE-2026-82762

Indicators of Compromise

• Unexpected child processes spawned by the device management or web service, particularly shells such as /bin/sh or /bin/bash.
• Outbound network connections from the device to unfamiliar IP addresses, including reverse shells or tool-download callbacks.
• Configuration or firmware modifications that were not initiated by an authorized administrator.
• Authentication log entries showing successful logins from unusual source addresses shortly before anomalous device behavior.

Detection Strategies

• Inspect HTTP or management-protocol request bodies for shell metacharacters (;, |, &, `, $() in fields that map to device configuration parameters.
• Correlate authentication events with process-execution telemetry from any network monitoring point that observes the device.
• Baseline expected outbound connections from FX-series devices and alert on deviations.

Monitoring Recommendations

• Forward device syslog and authentication events to a centralized logging platform for retention and correlation.
• Monitor management interface access with source-IP allow-listing and alert on logins outside approved administrative ranges.
• Track firmware version and configuration hashes to detect unauthorized changes.

How to Mitigate CVE-2026-82762

Immediate Actions Required

• Apply the vendor firmware update referenced in the Contec Security Information Document as soon as it is available for your model.
• Rotate all administrative credentials on affected FX5000, FX4000, and FX3000 devices.
• Restrict management-interface access to a dedicated administrative network segment.
• Audit recent authentication and configuration-change logs for indicators of exploitation.

Patch Information

Contec has published a security information document (contec_security_fl_26091000_en.pdf) describing affected models and remediation guidance. Coordinate with Contec support to confirm the fixed firmware version applicable to your specific FX-series model and deployment. See the JVN Security Advisory JVNVU99009004 for coordinated disclosure details.

Workarounds

• Place affected devices behind a firewall and permit management traffic only from designated jump hosts.
• Disable remote management interfaces where local console management is operationally sufficient.
• Enforce strong, unique credentials and, where supported, multi-factor authentication on the device management plane.
• Segment FX-series devices from general-purpose IT networks to limit blast radius if exploitation occurs.

# Example: restrict management access using upstream firewall rules
# Replace variables with the interface and admin subnet used in your environment
iptables -A FORWARD -s 10.10.20.0/24 -d <fx_device_ip> -p tcp --dport 443 -j ACCEPT
iptables -A FORWARD -d <fx_device_ip> -p tcp --dport 443 -j DROP