Adversaries may employ an encryption algorithm to conceal command and control traffic rather than relying on any inherent protections provided by a communication protocol. Despite the use of a secure algorithm, these implementations may be vulnerable to reverse engineering if secret keys are encoded and/or generated within malware samples/configuration files.
Unusual TLS tunnels through ports not normally encrypted (e.g., TLS on port 8080, 53). Defender sees NetFlow/IPFIX or packet inspection indicating high-entropy traffic volumes and asymmetric client/server exchange ratios.
Applications or launchd jobs initiating encrypted TLS traffic to rare external hosts. Defender observes unified logs showing ssl/TLS API calls by processes not baseline-approved, and payload entropy suggesting encrypted C2 sessions.
Processes that normally do not initiate network connections establishing outbound encrypted TLS/SSL sessions, especially with asymmetric traffic volumes (client sending more than receiving) or non-standard certificate chains. Defender observations correlate process creation with unexpected network encryption libraries being loaded.
SSL/TLS Inspection
SSL/TLS inspection involves decrypting encrypted network traffic to examine its content for signs of malicious activity. This capability is crucial for detecting threats that use encryption to evade detection, such as phishing, malware, or data exfiltration. After inspection, the traffic is re-encrypted and forwarded to its destination. This mitigation can be implemented through the following measures: Deploy SSL/TLS Inspection Appliances: - Implement SSL/TLS inspection solutions to decrypt and inspect encrypted traffic. - Ensure appliances are placed at critical network choke points for maximum coverage. Configure Decryption Policies: - Define rules to decrypt traffic for specific applications, ports, or domains. - Avoid decrypting sensitive or privacy-related traffic, such as financial or healthcare websites, to comply with regulations. Integrate Threat Intelligence: - Use threat intelligence feeds to correlate inspected traffic with known indicators of compromise (IOCs). Integrate with Security Tools: - Combine SSL/TLS inspection with SIEM and NDR tools to analyze decrypted traffic and generate alerts for suspicious activity. - Example Tools: Splunk, Darktrace Implement Certificate Management: - Use trusted internal or third-party certificates for traffic re-encryption after inspection. - Regularly update certificate authorities (CAs) to ensure secure re-encryption. Monitor and Tune: - Continuously monitor SSL/TLS inspection logs for anomalies and fine-tune policies to reduce false positives.
Network Intrusion Prevention
Use intrusion detection signatures to block traffic at network boundaries.