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MOXA Weak Entropy in DSA Keys Vulnerability

Low RiskICS-CERT ICSA-13-217-01May 8, 2013
Summary

Moxa OnCell Gateway models G3111, G3151, G3211, and G3251 with firmware versions prior to 1.4 generate DSA cryptographic keys with weak entropy. This reduces the strength of the keys and makes them susceptible to cryptanalysis attacks. The vulnerability affects SSH and other services that rely on DSA-based authentication on these cellular industrial gateways.

What this means
What could happen
An attacker could potentially compromise the cryptographic authenticity of DSA-secured connections to the gateway, allowing unauthorized remote access to the device and its management interfaces without valid credentials.
Who's at risk
Operators of Moxa OnCell Gateway models G3111, G3151, G3211, and G3251 should care about this issue. These are cellular industrial gateways commonly used in remote water or power substations, remote terminal units (RTUs), and field equipment monitoring. Organizations running firmware versions prior to 1.4 are at risk.
How it could be exploited
An attacker with network access to the gateway's SSH or other DSA-authenticated service could perform cryptanalysis on the weak DSA keys. Once the private key is recovered, the attacker gains authenticated access to the device and can modify configurations, stop communications, or alter process parameters.
Prerequisites
  • Network access to SSH port or other DSA-authenticated service on the OnCell Gateway
  • Weak DSA keys must be present (firmware version before 1.4)
  • Time and computational resources to perform cryptanalysis on the weak entropy keys
remotely exploitableweak cryptographyno patch available for current versionsaffects remote management interfaces
Exploitability
Low exploit probability (EPSS 0.5%)
Affected products (4)
4 pending
ProductAffected VersionsFix Status
OnCell Gateway models G3111: <firmware_1.4<firmware 1.4No fix yet
OnCell Gateway models G3151: <firmware_1.4<firmware 1.4No fix yet
OnCell Gateway models G3211: <firmware_1.4<firmware 1.4No fix yet
OnCell Gateway models G3251: <firmware_1.4<firmware 1.4No fix yet
Remediation & Mitigation
0/4
Do now
0/2
WORKAROUNDIsolate affected OnCell Gateways from untrusted networks using firewall rules to restrict SSH and remote management access to authorized workstations only
WORKAROUNDDisable remote management services (SSH, Telnet) on the gateway if not actively required for operations
Schedule — requires maintenance window
0/1

Patching may require device reboot — plan for process interruption

HOTFIXRegenerate all DSA keys on affected gateways after firmware upgrade to version 1.4 or later is available
Long-term hardening
0/1
HARDENINGImplement network segmentation to place OnCell Gateways on a restricted industrial network segment with access controls between it and corporate/external networks
View full CISA ICS-CERT advisory
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MOXA Weak Entropy in DSA Keys Vulnerability - OTPulse