A critical vulnerability in the Ubiquiti UniFi Network Controller allows attackers on an adjacent network to intercept sensitive SMTP credentials via man in the middle attacks.

The application fails to properly validate SSL certificates during SMTP connections, which allows unauthenticated attackers situated on the adjacent network to conduct man in the middle attacks.

The exploitation of this vulnerability can lead to the unauthorized interception of sensitive SMTP credentials, potentially granting attackers access to internal email communications or mail relay services. With a CVSS score of 7.5, this high severity flaw poses a significant risk to organizational confidentiality and could facilitate further unauthorized access or lateral movement within the network.

Immediate Action: Update the UniFi Network Controller to version 5.10.22, 5.11.18, or later to implement proper certificate validation.

Proactive Monitoring: Monitor network traffic for anomalous SMTP connections or unexpected certificate validation errors originating from the controller host.

Compensating Controls: Ensure that the controller is restricted to trusted management segments and implement network segmentation to prevent unauthorized access from untrusted adjacent network devices.

Public Exploit Available: Unknown

Given the potential for credential theft, administrators should prioritize updating to the patched versions provided by Ubiquiti. Organizations that cannot immediately update should restrict network access to the controller to authorized personnel only to mitigate the risk of adjacent network attacks.