CVE-2025-55069 Overview
A predictable seed in pseudo-random number generator (PRNG) vulnerability has been discovered in firmware version 3.60 of the Click Plus PLC. The vulnerability stems from the software implementing a predictable seed for its pseudo-random number generator, which fundamentally compromises the security of any cryptographic private keys generated by the device. This weakness allows attackers to potentially predict or reconstruct private keys, undermining the entire cryptographic security model of affected industrial control systems.
Critical Impact
Attackers with network access can exploit the predictable PRNG seed to compromise private key generation, potentially enabling unauthorized access, man-in-the-middle attacks, or complete authentication bypass on industrial control systems.
Affected Products
- AutomationDirect Click Plus PLC - Firmware version 3.60
Discovery Timeline
- 2025-09-23 - CVE-2025-55069 published to NVD
- 2026-04-15 - Last updated in NVD database
Technical Details for CVE-2025-55069
Vulnerability Analysis
This vulnerability is classified under CWE-337 (Predictable Seed in Pseudo-Random Number Generator), a cryptographic weakness that occurs when a random number generator uses a predictable or insufficiently random seed value. In the case of the Click Plus PLC firmware 3.60, the PRNG seed can be predicted by an attacker, which means any cryptographic operations relying on the randomness—such as private key generation, session token creation, or nonce generation—are fundamentally insecure.
The attack can be conducted over the network without requiring any privileges on the target system. However, some user interaction may be required to trigger the vulnerable code path. Once exploited, an attacker could recover or predict the private keys generated by the PLC, potentially gaining the ability to impersonate the device, decrypt sensitive communications, or forge authenticated messages.
Root Cause
The root cause lies in the implementation of the pseudo-random number generator within the Click Plus PLC firmware. Rather than using a cryptographically secure source of entropy (such as hardware-based random number generators or system noise), the firmware uses a predictable seed—possibly based on easily obtainable values like system time, device serial numbers, or other deterministic inputs. This design flaw means that an attacker who can determine or guess the seed value can reproduce the entire sequence of "random" numbers generated by the device.
Attack Vector
The attack vector is network-based. An attacker with network connectivity to the vulnerable Click Plus PLC can:
- Identify the device and determine it is running vulnerable firmware version 3.60
- Analyze the predictable seed mechanism through firmware reverse engineering or traffic analysis
- Reconstruct or predict the PRNG output sequence
- Derive any private keys or cryptographic material generated using the compromised PRNG
- Use the recovered keys to authenticate as the device, decrypt communications, or perform other malicious actions
The attack requires no prior authentication or privileges on the target device, though some user interaction may be needed depending on the specific exploitation scenario.
Detection Methods for CVE-2025-55069
Indicators of Compromise
- Unexpected authentication attempts from untrusted sources using valid-appearing credentials
- Network traffic patterns indicating key enumeration or brute-force attempts against PLC devices
- Unauthorized configuration changes to Click Plus PLC devices
- Anomalous encrypted communications that may indicate key compromise
Detection Strategies
- Monitor network traffic to and from Click Plus PLC devices for unusual patterns or volumes
- Implement network segmentation to isolate PLCs and detect lateral movement attempts
- Deploy ICS-specific intrusion detection systems capable of analyzing industrial protocol traffic
- Compare firmware versions across all Click Plus devices to identify vulnerable installations running version 3.60
Monitoring Recommendations
- Enable logging on network devices monitoring PLC communication segments
- Establish baseline communication patterns for industrial control systems and alert on deviations
- Monitor for unauthorized firmware download attempts from AutomationDirect Software Downloads
- Review the CISA ICS Advisory ICSA-25-266-01 for additional detection guidance
How to Mitigate CVE-2025-55069
Immediate Actions Required
- Identify all Click Plus PLC devices running firmware version 3.60 in your environment
- Isolate affected devices behind firewalls and restrict network access to essential personnel only
- Rotate any cryptographic keys or credentials that may have been generated by affected devices
- Implement network segmentation to limit exposure of industrial control systems
- Review and apply the latest firmware updates from AutomationDirect
Patch Information
AutomationDirect has released firmware updates to address this vulnerability. Administrators should download the latest firmware from the AutomationDirect Software Downloads page. After updating, any keys or cryptographic material generated by the vulnerable firmware should be regenerated to ensure they are not compromised.
For detailed guidance, refer to the CISA ICS Advisory ICSA-25-266-01.
Workarounds
- Implement strict network segmentation to isolate PLCs from untrusted networks
- Use external cryptographic key management solutions rather than relying on keys generated by the PLC
- Deploy VPN or encrypted tunnels for all communication with affected devices
- Restrict physical and network access to PLCs to authorized personnel only
- Monitor for anomalous authentication attempts until patches can be applied
# Example: Network isolation using firewall rules
# Restrict access to PLC network segment (adjust IPs as needed)
iptables -A INPUT -s 10.0.0.0/24 -d 192.168.100.0/24 -j ACCEPT
iptables -A INPUT -d 192.168.100.0/24 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
