CVE-2025-2026 Overview
CVE-2025-2026 is a high-severity vulnerability affecting the Moxa NPort 6100-G2 and 6200-G2 Series secure serial device servers. The flaw allows an authenticated remote attacker with web read-only privileges to perform a null byte injection through the device's web Application Programming Interface (API). Successful exploitation triggers an unexpected device reboot, producing a denial-of-service (DoS) condition. The weakness is classified as [CWE-170] Improper Null Termination. Moxa published advisory MPSA-251731 documenting the issue alongside CVE-2025-1977.
Critical Impact
A low-privileged remote attacker can force the affected NPort device to reboot, disrupting serial-to-Ethernet communications for connected industrial systems.
Affected Products
- Moxa NPort 6100-G2 Series secure serial device servers
- Moxa NPort 6200-G2 Series secure serial device servers
- Web management API exposed by the affected firmware
Discovery Timeline
- 2025-12-31 - CVE-2025-2026 published to the National Vulnerability Database (NVD)
- 2026-04-15 - Last updated in NVD database
Technical Details for CVE-2025-2026
Vulnerability Analysis
The vulnerability resides in the web API exposed by the NPort 6100-G2 and 6200-G2 Series firmware. The API fails to properly handle embedded null bytes (\\x00) within user-supplied input. When a crafted request containing a null byte reaches a vulnerable endpoint, internal string handling routines terminate prematurely or misinterpret buffer boundaries. The resulting inconsistent state causes the device to reboot.
Exploitation requires authentication, but only web read-only credentials are necessary. This significantly lowers the bar for abuse in environments where monitoring or auditor accounts exist on field devices. NPort serial device servers commonly bridge legacy serial equipment to TCP/IP networks in industrial control system (ICS) deployments, so a forced reboot can interrupt SCADA polling and other deterministic communications.
Root Cause
The root cause is improper null termination [CWE-170] within the web API request parser. Input strings are accepted without sanitizing or rejecting embedded null characters before being passed to lower-level routines that assume well-formed, null-terminated data.
Attack Vector
The attack is delivered over the network against the device's web management interface. An authenticated attacker submits a malicious API request containing one or more null bytes in a parameter. No user interaction is required beyond the attacker's own session. Refer to the Moxa Security Advisory MPSA-251731 for the affected endpoint and parameter details.
No public proof-of-concept exploit code is available, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog.
Detection Methods for CVE-2025-2026
Indicators of Compromise
- Unscheduled reboots of NPort 6100-G2 or 6200-G2 devices recorded in syslog or device event logs
- Web API requests containing encoded null bytes (%00) directed at the device management interface
- Authenticated sessions originating from read-only accounts immediately preceding a device restart
Detection Strategies
- Inspect HTTP and HTTPS traffic to NPort management interfaces for request bodies or query parameters containing null byte sequences
- Correlate web authentication events with subsequent device reboot events to identify suspicious patterns
- Alert on repeated reboots of the same NPort device within short time windows, indicating possible DoS attempts
Monitoring Recommendations
- Forward NPort syslog data to a centralized Security Information and Event Management (SIEM) platform for analysis
- Monitor read-only service accounts on field devices for unexpected API activity outside normal maintenance windows
- Track availability metrics for serial-to-Ethernet bridges to surface communication outages caused by reboots
How to Mitigate CVE-2025-2026
Immediate Actions Required
- Apply the firmware update referenced in Moxa advisory MPSA-251731 to all NPort 6100-G2 and 6200-G2 Series devices
- Restrict network access to the device web API to trusted management hosts and jump servers only
- Audit existing user accounts on affected devices and remove unnecessary read-only or service accounts
- Rotate credentials for any accounts that may have been exposed prior to patching
Patch Information
Moxa has published remediation guidance in Security Advisory MPSA-251731. Administrators should consult the advisory for the fixed firmware versions and upgrade procedures specific to each affected model.
Workarounds
- Place affected NPort devices behind a firewall that blocks inbound web management traffic from untrusted networks
- Disable the web management interface where command-line or out-of-band management is feasible
- Enforce strong, unique passwords on all device accounts and apply the principle of least privilege
- Segment industrial control networks to limit lateral access to NPort management interfaces
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
