CVE-2025-6950: Moxa Hard-coded JWT Auth Bypass Vulnerability

CVE-2025-6950 Overview

A critical Use of Hard-coded Credentials vulnerability (CWE-798) has been identified in Moxa's network security appliances and routers. The system employs a hard-coded secret key to sign JSON Web Tokens (JWT) used for authentication. This insecure implementation allows an unauthenticated attacker to forge valid tokens, thereby bypassing authentication controls and impersonating any user. Exploitation of this vulnerability can result in complete system compromise, enabling unauthorized access, data theft, and full administrative control over the affected device.

Critical Impact

Successful exploitation allows unauthenticated attackers to forge JWT tokens, bypass authentication entirely, and gain full administrative control over affected Moxa network appliances and routers.

Affected Products

• Moxa Network Security Appliances
• Moxa Routers
• Devices referenced in MPSA-258121 security advisory

Discovery Timeline

• October 17, 2025 - CVE-2025-6950 published to NVD
• October 21, 2025 - Last updated in NVD database

Technical Details for CVE-2025-6950

Vulnerability Analysis

This vulnerability stems from insecure cryptographic implementation in Moxa's authentication system. The affected devices use JSON Web Tokens (JWT) for session authentication, but the secret key used to sign these tokens is hard-coded directly into the firmware or application code. This fundamental security flaw means that any attacker who discovers or extracts this static secret key can generate valid authentication tokens without ever needing legitimate credentials.

The impact is severe as the vulnerability requires no prior authentication and can be exploited remotely over the network. An attacker can craft malicious JWT tokens that the system will accept as legitimate, allowing them to impersonate any user account including administrators. This grants complete control over the affected device, potentially compromising the confidentiality, integrity, and availability of the network appliance itself. While the vulnerability does not directly propagate to downstream systems, the compromised device could be used as a pivot point for further attacks on the network infrastructure.

Root Cause

The root cause of CVE-2025-6950 is the use of hard-coded credentials embedded within the device firmware. Specifically, the JWT signing key is statically defined rather than being generated uniquely per device or installation. This violates fundamental security principles as the same secret key exists across all deployed instances of the affected products, making it a single point of failure. Once the key is extracted from any device or reverse-engineered from firmware, all devices using the same key become vulnerable.

Attack Vector

The attack can be executed remotely over the network without requiring any user interaction or prior authentication. An attacker would need to:

1. Obtain the hard-coded JWT secret key (through firmware analysis or public disclosure)
2. Craft a JWT token with arbitrary claims, including administrative privileges
3. Sign the forged token using the known secret key
4. Send authenticated requests to the device using the forged token
5. Gain complete administrative access to perform any operation

The vulnerability exploitation follows a straightforward process where an attacker extracts the hard-coded secret key from device firmware, then uses standard JWT libraries to create tokens with elevated privileges. Once signed with the known key, these forged tokens are accepted by the device as legitimate authentication credentials, granting full system access.

Detection Methods for CVE-2025-6950

Indicators of Compromise

• Unusual administrative login events from unexpected IP addresses or at abnormal times
• JWT tokens appearing in logs with suspicious claim values or unexpected user identifiers
• Multiple authentication sessions for the same user from different geographic locations
• Administrative actions performed without corresponding login events from the web interface
• Network traffic containing JWT tokens with anomalous or forged timestamps

Detection Strategies

• Implement network monitoring to detect authentication requests to affected Moxa devices from untrusted sources
• Review authentication logs for signs of token-based access that doesn't correlate with legitimate user activity
• Deploy intrusion detection rules to flag JWT authentication attempts containing known malicious patterns
• Monitor for firmware extraction attempts or unusual debugging connections to affected devices

Monitoring Recommendations

• Enable comprehensive logging on all affected Moxa network appliances and centralize log collection
• Implement alerting for any administrative actions performed on critical network infrastructure devices
• Establish baseline normal authentication patterns and flag deviations
• Monitor network segments containing affected devices for reconnaissance activity

How to Mitigate CVE-2025-6950

Immediate Actions Required

• Consult the Moxa Security Advisory MPSA-258121 for official patches and firmware updates
• Isolate affected Moxa devices from untrusted networks until patches can be applied
• Implement strict network access controls to limit which hosts can communicate with affected devices
• Audit administrative accounts and review recent access logs for signs of compromise

Patch Information

Moxa has released security advisory MPSA-258121 addressing CVE-2025-6950 along with several related vulnerabilities (CVE-2025-6892, CVE-2025-6893, CVE-2025-6894, CVE-2025-6949). Organizations should review the official Moxa security advisory for specific firmware versions and update instructions applicable to their deployed products.

Workarounds

• Place affected devices behind network firewalls or access control lists restricting management interface access to trusted administrator IPs only
• Implement network segmentation to isolate industrial control and network infrastructure devices from general network traffic
• Deploy a VPN or jump host requirement for all administrative access to affected Moxa equipment
• Consider temporarily disabling remote management interfaces until patches are applied, using only local console access
• Implement additional authentication layers such as a reverse proxy with separate authentication in front of affected devices

# Example firewall configuration to restrict management access
# Adjust IPs and interfaces for your environment

# Allow management access only from trusted admin network
iptables -A INPUT -p tcp --dport 443 -s 10.0.100.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP

# Block management interface from untrusted networks
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 8080 -j DROP