Adversaries may use an existing, legitimate external Web service to exfiltrate data rather than their primary command and control channel. Popular Web services acting as an exfiltration mechanism may give a significant amount of cover due to the likelihood that hosts within a network are already communicating with them prior to compromise. Firewall rules may also already exist to permit traffic to these services. Web service providers also commonly use SSL/TLS encryption, giving adversaries an added level of protection.
Abnormal API calls from user accounts invoking file upload endpoints outside normal baselines (M365, Google Drive, Box). Defender perspective: monitor unified audit logs for elevated frequency of Upload, Create, or Copy operations from compromised accounts.
Processes that normally do not initiate network communications suddenly making outbound HTTPS connections with high outbound-to-inbound data ratios. Defender view: correlation between process creation logs (e.g., Word, Excel, PowerShell) and subsequent anomalous network traffic volumes toward common web services (Dropbox, Google Drive, OneDrive).
Processes (tar, curl, python scripts) accessing large file sets and initiating outbound HTTPS POST requests with payload sizes inconsistent with baseline activity. Defender perspective: detect abnormal sequence of file archival followed by encrypted uploads to external web services.
Restrict Web-Based Content
Restricting web-based content involves enforcing policies and technologies that limit access to potentially malicious websites, unsafe downloads, and unauthorized browser behaviors. This can include URL filtering, download restrictions, script blocking, and extension control to protect against exploitation, phishing, and malware delivery. This mitigation can be implemented through the following measures: Deploy Web Proxy Filtering: - Use solutions to filter web traffic based on categories, reputation, and content types. - Enforce policies that block unsafe websites or file types at the gateway level. Enable DNS-Based Filtering: - Implement tools to restrict access to domains associated with malware or phishing campaigns. - Use public DNS filtering services to enhance protection. Enforce Content Security Policies (CSP): - Configure CSP headers on internal and external web applications to restrict script execution, iframe embedding, and cross-origin requests. Control Browser Features: - Disable unapproved browser features like automatic downloads, developer tools, or unsafe scripting. - Enforce policies through tools like Group Policy Management to control browser settings. Monitor and Alert on Web-Based Threats: - Use SIEM tools to collect and analyze web proxy logs for signs of anomalous or malicious activity. - Configure alerts for access attempts to blocked domains or repeated file download failures.
Data Loss Prevention
Data Loss Prevention (DLP) involves implementing strategies and technologies to identify, categorize, monitor, and control the movement of sensitive data within an organization. This includes protecting data formats indicative of Personally Identifiable Information (PII), intellectual property, or financial data from unauthorized access, transmission, or exfiltration. DLP solutions integrate with network, endpoint, and cloud platforms to enforce security policies and prevent accidental or malicious data leaks. (Citation: PurpleSec Data Loss Prevention) This mitigation can be implemented through the following measures: Sensitive Data Categorization: - Use Case: Identify and classify data based on sensitivity (e.g., PII, financial data, trade secrets). - Implementation: Use DLP solutions to scan and tag files containing sensitive information using predefined patterns, such as Social Security Numbers or credit card details. Exfiltration Restrictions: - Use Case: Prevent unauthorized transmission of sensitive data. - Implementation: Enforce policies to block unapproved email attachments, unauthorized USB usage, or unencrypted data uploads to cloud storage. Data-in-Transit Monitoring: - Use Case: Detect and prevent the transmission of sensitive data over unapproved channels. - Implementation: Deploy network-based DLP tools to inspect outbound traffic for sensitive content (e.g., financial records or PII) and block unapproved transmissions. Endpoint Data Protection: - Use Case: Monitor and control sensitive data usage on endpoints. - Implementation: Use endpoint-based DLP agents to block copy-paste actions of sensitive data and unauthorized printing or file sharing. Cloud Data Security: - Use Case: Protect data stored in cloud platforms. - Implementation: Integrate DLP with cloud storage platforms like Google Drive, OneDrive, or AWS to monitor and restrict sensitive data sharing or downloads.