Communications over SSL

Hunt Hypothesis

Unusual SSL communications may indicate covert data exfiltration or command and control activity. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify potential adversary persistence or data leakage attempts that evade traditional detection methods.

YARA Rule

rule network_ssl {
    meta:
        author = "x0r"
        description = "Communications over SSL"
        version = "0.1"
    strings:
        $f1 = "ssleay32.dll" nocase
        $f2 = "libeay32.dll" nocase
        $f3 = "libssl32.dll" nocase
        $c1 = "IdSSLOpenSSL" nocase
    condition:
        any of them
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

• Microsoft Defender for Endpoint — Custom indicators / advanced hunting
• Email Gateway — Attachment scanning
• File Share Monitoring — Periodic scanning of shared drives
• YARA CLI — Manual threat hunting on endpoints

This rule contains 4 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: System update via HTTPS
  Description: A legitimate system update process uses HTTPS to communicate with a trusted update server.
  Filter/Exclusion: Exclude traffic to known update servers (e.g., update.microsoft.com, download.docker.com) or use a filter based on the destination IP or domain.

• Scenario: Admin access via SSH tunnel
  Description: An administrator uses an SSH tunnel to securely access internal services, which may appear as SSL traffic.
  Filter/Exclusion: Exclude traffic originating from known admin workstations or use a filter based on source IP and port 22 (SSH).

• Scenario: Scheduled backup over HTTPS
  Description: A scheduled backup job uses HTTPS to transfer data to a backup server.
  Filter/Exclusion: Exclude traffic to known backup servers (e.g., backup.example.com) or use a filter based on the destination port (443) and destination IP.

• Scenario: Internal service communication via HTTPS
  Description: Internal services (e.g., Kubernetes API, internal API gateways) communicate over HTTPS, which may be flagged as suspicious.
  Filter/Exclusion: Exclude traffic between internal IPs or use a filter based on the source and destination IP ranges within the corporate network.

• Scenario: Email encryption via S/MIME
  Description: Email clients use S/MIME encryption to send encrypted emails, which may be mistaken for SSL traffic.
  Filter/Exclusion: Exclude traffic involving email clients (e.g., Microsoft Outlook, Thunderbird) or use a filter based on the application name or process name.