CVE-2026-109813: Moxa Hard-Coded Key Information Disclosure

CVE-2026-109813 Overview

CVE-2026-109813 is a hard-coded cryptographic key vulnerability in the /usr/bin/sysman binary shipped with several of Moxa's industrial computing products. The embedded private key material is identical across affected devices and can be extracted from any single unit. An unauthenticated attacker with adjacent network access can abuse the exposed key to decrypt or forge communications, breaking confidentiality and integrity guarantees. The flaw is tracked under CWE-321: Use of Hard-coded Cryptographic Key and is documented in the Moxa Security Advisory MPSA-262560.

Critical Impact
An unauthenticated attacker on an adjacent network can leverage the embedded private key to compromise the confidentiality and integrity of device communications.

Affected Products

Moxa industrial computing products containing the vulnerable /usr/bin/sysman binary
Specific affected models and firmware versions are listed in Moxa advisory MPSA-262560
Refer to the vendor advisory for the authoritative product and firmware matrix

Discovery Timeline

2026-10-16 - CVE-2026-109813 published to NVD
2026-10-16 - Last updated in NVD database

Technical Details for CVE-2026-109813

Vulnerability Analysis

The /usr/bin/sysman system management utility ships with cryptographic key material compiled directly into the binary. Because the key is static across all deployed devices, extracting it from one unit yields a key that unlocks every other affected device. An attacker who obtains the key can decrypt intercepted traffic, impersonate the device, or inject forged management messages. The adjacent network attack requirement means the adversary must sit on the same logical network segment as the target, which is realistic in flat operational technology (OT) environments.

Root Cause

The root cause is the inclusion of private key material inside a distributed binary rather than per-device key provisioning. This design pattern, catalogued as CWE-321, eliminates the asymmetry that cryptography depends on. Once the binary is reverse engineered, the trust model collapses for every device sharing that firmware image.

Attack Vector

Exploitation requires adjacent network access, no authentication, and no user interaction. An attacker extracts the private key from a firmware image or a captured device, then uses it against production units reachable from the same broadcast domain, VLAN, or routed OT segment. With the key in hand, the attacker can perform man-in-the-middle decryption of management sessions or forge signed payloads accepted by sysman. No proof-of-concept exploit is publicly listed for CVE-2026-109813 at the time of publication.

See the Moxa Security Advisory MPSA-262560 for vendor-supplied technical details.

Detection Methods for CVE-2026-109813

Indicators of Compromise

Unexpected management sessions to Moxa device TCP/UDP services originating from untrusted hosts on the same OT segment.
Successful authenticated sysman interactions from endpoints that have never previously communicated with the device.
Anomalous configuration changes or firmware operations with no corresponding operator ticket or change record.

Detection Strategies

Baseline the normal set of workstations and engineering stations that talk to each Moxa device, then alert on deviations.
Inspect network traffic for repeated TLS or application-layer handshakes using the same static certificate or key fingerprint across unrelated devices.
Correlate device management-plane access with identity telemetry to detect sessions that bypass expected administrative accounts.

Monitoring Recommendations

Forward Moxa device logs and OT network flow data into a centralized data lake for cross-device correlation and historical hunting.
Monitor east-west traffic within OT VLANs for lateral attempts to reach sysman service ports.
Alert on any firmware version regression or configuration rollback that could indicate attacker tampering.

How to Mitigate CVE-2026-109813

Immediate Actions Required

Inventory all Moxa industrial computers and cross-reference models and firmware against the MPSA-262560 affected list.
Restrict management-plane access to Moxa devices using network segmentation, firewall rules, and jump-host enforcement.
Disable or firewall the sysman service on devices that cannot be patched immediately.
Rotate any shared secrets, certificates, or credentials that may have transited management channels protected by the hard-coded key.

Patch Information

Moxa has published guidance in Security Advisory MPSA-262560 covering CVE-2026-109812 and CVE-2026-109813. Apply the firmware updates and configuration changes specified in that advisory to the affected models. Follow the vendor's recommended sequence for firmware upgrade and post-upgrade validation to ensure the new, per-device or properly provisioned keys are in effect.

Workarounds

Place affected devices behind an industrial firewall or data diode that terminates management traffic and allows only approved engineering stations.
Enforce strict VLAN isolation so adjacent-network reachability to sysman is limited to a minimal, monitored administrative segment.
Where feasible, overlay an authenticated VPN or IPsec tunnel for all device management traffic rather than relying on the device's embedded cryptography.
Increase logging verbosity on Moxa devices and surrounding network infrastructure until patches are applied.

bash

# Example: restrict sysman management access to a dedicated admin subnet
# Replace interface, admin subnet, and sysman port with values from MPSA-262560
iptables -A INPUT -p tcp --dport <SYSMAN_PORT> -s 10.10.50.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport <SYSMAN_PORT> -j DROP