Adversaries may attempt to use bots to successfully solve CAPTCHA challenges. CAPTCHA challenges are typically used by defenders to detect and prevent bot and spam traffic from accessing protected webpages. CAPTCHAs are automated tests often placed before login screens or form fields. Traditional CAPTCHAs ask the user to decipher a string of characters, type the characters into a box, and submit the form. reCAPTCHA asks the user to identify images, click a checkbox, or evaluate the user’s behavior from mouse movement and device cookies.(Citation: CAPTCHAS Cloudflare) Adversaries may use scripts or toolkits to automatically solve the CAPTCHA puzzle. For example, adversaries may develop a script that uses the ImageMagick toolkit to solve the CAPTCHA puzzles to then create multiple valid accounts. ImageMagick tool can convert the images into a RGB complemented image. The CAPTCHA challenge may be solved by identifying and comparing attributes of the RGB images to select the expected image.(Citation: Free Trial PurpleUrchin) Once the CAPTCHA challenge is solved, the adversary’s script may access the protected page. After accessing the protected the page, the adversary may submit valid forms to the target.
Use intrusion detection signatures to block traffic at network boundaries.
M1037Filter Network TrafficEmploy network appliances and endpoint software to filter ingress, egress, and lateral network traffic. This includes protocol-based filtering, enforcing firewall rules, and blocking or restricting traffic based on predefined conditions to limit adversary movement and data exfiltration. This mitigation can be implemented through the following measures: Ingress Traffic Filtering: - Use Case: Configure network firewalls to allow traffic only from authorized IP addresses to public-facing servers. - Implementation: Limit SSH (port 22) and RDP (port 3389) traffic to specific IP ranges. Egress Traffic Filtering: - Use Case: Use firewalls or endpoint security software to block unauthorized outbound traffic to prevent data exfiltration and command-and-control (C2) communications. - Implementation: Block outbound traffic to known malicious IPs or regions where communication is unexpected. Protocol-Based Filtering: - Use Case: Restrict the use of specific protocols that are commonly abused by adversaries, such as SMB, RPC, or Telnet, based on business needs. - Implementation: Disable SMBv1 on endpoints to prevent exploits like EternalBlue. Network Segmentation: - Use Case: Create network segments for critical systems and restrict communication between segments unless explicitly authorized. - Implementation: Implement VLANs to isolate IoT devices or guest networks from core business systems. Application Layer Filtering: - Use Case: Use proxy servers or Web Application Firewalls (WAFs) to inspect and block malicious HTTP/S traffic. - Implementation: Configure a WAF to block SQL injection attempts or other web application exploitation techniques.
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