Adversaries may use an existing, legitimate external Web service to host information that points to additional command and control (C2) infrastructure. Adversaries may post content, known as a dead drop resolver, on Web services with embedded (and often obfuscated/encoded) domains or IP addresses. Once infected, victims will reach out to and be redirected by these resolvers. Popular websites and social media acting as a mechanism for C2 may give a significant amount of cover due to the likelihood that hosts within a network are already communicating with them prior to a compromise. Using common services, such as those offered by Google or Twitter, makes it easier for adversaries to hide in expected noise. Web service providers commonly use SSL/TLS encryption, giving adversaries an added level of protection. Use of a dead drop resolver may also protect back-end C2 infrastructure from discovery through malware binary analysis while also enabling operational resiliency (since this infrastructure may be dynamically changed).
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.
M1031Network Intrusion PreventionUse intrusion detection signatures to block traffic at network boundaries.
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