CVE-2026-3868: Moxa Secure Router DoS Vulnerability

CVE-2026-3868 Overview

CVE-2026-3868 is an improper handling of length parameter inconsistency vulnerability (CWE-130) identified in Moxa's Secure Router. The vulnerability exists within the HTTPS management interface, where improper validation of length parameters allows an unauthenticated remote attacker to send specially crafted requests that trigger a buffer overflow condition. This results in the web service becoming unresponsive, causing a denial-of-service (DoS) condition that requires a device reboot to restore normal operation.

Critical Impact

Unauthenticated remote attackers can crash the HTTPS management interface of affected Moxa Secure Routers, severely impacting device availability and requiring manual intervention to restore service.

Affected Products

• Moxa Secure Router (specific models detailed in vendor advisory)

Discovery Timeline

• April 27, 2026 - CVE-2026-3868 published to NVD
• April 27, 2026 - Last updated in NVD database

Technical Details for CVE-2026-3868

Vulnerability Analysis

This vulnerability stems from improper handling of length parameter inconsistency (CWE-130) in the HTTPS management interface of Moxa Secure Routers. The flaw occurs when the web service fails to properly validate length parameters in incoming requests, creating a condition where specially crafted input can overflow internal buffers.

The attack requires no authentication or user interaction, making it particularly concerning for internet-exposed devices. An attacker operating from the network can send malicious requests to the HTTPS management interface that exploit the length parameter validation weakness. When triggered, the buffer overflow causes the web service to crash, rendering the management interface unavailable until the device is rebooted.

While successful exploitation severely impacts device availability, the vulnerability scope is limited to the affected device itself. According to the vendor advisory, no confidentiality or integrity impact has been identified for either the affected product or subsequent systems connected to it.

Root Cause

The root cause lies in improper validation of length parameters within the HTTPS management interface request handling code. When processing incoming requests, the application fails to adequately verify that length values specified by clients match the actual data provided or fall within expected bounds. This mismatch between declared and actual lengths leads to buffer overflow conditions when the service attempts to process malformed requests.

Attack Vector

The attack vector is network-based, requiring only network access to the HTTPS management interface of vulnerable Moxa Secure Routers. The attack characteristics include:

• No authentication required - The attacker does not need valid credentials
• No user interaction needed - The attack can be executed automatically without victim involvement
• Remote exploitation - The attack can be launched from anywhere with network connectivity to the target device
• Low complexity - No specialized conditions or circumstances are needed beyond basic network access

An attacker would craft HTTPS requests to the management interface containing length parameter values that do not match the actual payload size, triggering the buffer overflow when the service attempts to process the inconsistent data.

Detection Methods for CVE-2026-3868

Indicators of Compromise

• Unexpected crashes or restarts of the HTTPS management web service on Moxa Secure Routers
• Management interface becoming unresponsive without corresponding system maintenance activities
• Unusual patterns of HTTPS requests to the router management port (typically port 443)
• Log entries indicating service crashes or buffer-related errors prior to web service failures

Detection Strategies

• Monitor for repeated HTTPS requests with malformed or inconsistent length headers targeting management interfaces
• Implement network-based intrusion detection rules to identify anomalous traffic patterns to Moxa router management ports
• Deploy anomaly detection for web service availability, alerting on unexpected management interface outages
• Review device logs for service restart patterns that may indicate exploitation attempts

Monitoring Recommendations

• Enable comprehensive logging on Moxa Secure Router management interfaces
• Implement network monitoring for unusual traffic volumes or patterns to router management ports
• Set up automated alerting for management interface availability degradation
• Consider deploying network sensors to capture and analyze traffic to critical network infrastructure devices

How to Mitigate CVE-2026-3868

Immediate Actions Required

• Restrict network access to the HTTPS management interface to trusted administrative networks only
• Implement firewall rules to block external access to router management ports
• Enable VPN requirements for remote management access
• Review and audit current management interface exposure to identify affected devices

Patch Information

Moxa has released a security advisory addressing this vulnerability. Administrators should consult the Moxa Security Advisory MPSA-261521 for specific patch information, affected firmware versions, and updated firmware downloads.

Workarounds

• Isolate Moxa Secure Routers on a dedicated management VLAN accessible only to authorized administrators
• Implement network access control lists (ACLs) to restrict management interface access to specific IP addresses
• Consider disabling HTTPS management access if not required and use alternative out-of-band management methods
• Deploy a web application firewall or reverse proxy in front of management interfaces to filter malformed requests

# Example firewall rule to restrict management access (adapt to your environment)
# Allow management access only from trusted admin network
iptables -A INPUT -p tcp --dport 443 -s 192.168.100.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP