Ruby and Ruby on Rails Vulnerability Allows Code Execution

A vulnerability exists in Ruby and Ruby on Rails that allows a remote, anonymous attacker to bypass security measures and execute arbitrary code. This vulnerability stems from an unspecified flaw within the erb gem, a templating engine used by Rails and other Ruby applications. The lack of specific CVE identification makes precise targeting difficult, but exploitation could lead to complete system compromise if successful. Defenders should prioritize monitoring for suspicious activity related to Ruby and Rails applications.

Attack Chain

1. The attacker identifies a Ruby or Ruby on Rails application utilizing the erb gem.
2. The attacker crafts a malicious input designed to exploit the vulnerability in the erb gem. This input is often injected through user-supplied data, such as form fields or API requests.
3. The attacker sends the crafted input to the vulnerable application, potentially through a web request.
4. The application processes the malicious input using the erb gem, leading to code execution.
5. The attacker gains the ability to execute arbitrary commands on the server running the application.
6. The attacker uses the initial access to escalate privileges on the system.
7. The attacker deploys persistent backdoors for continued access.
8. The attacker pivots to other systems on the network or exfiltrates sensitive data.

Impact

Successful exploitation of this vulnerability allows a remote attacker to execute arbitrary code on the affected system. This can lead to complete system compromise, data theft, and further lateral movement within the network. The lack of detailed reporting makes it difficult to assess the scale of prior attacks.

Recommendation

• Enable detailed logging for your Ruby and Ruby on Rails applications, specifically focusing on web requests and application logs to detect suspicious activity related to the erb gem.
• Deploy the Sigma rules provided in this brief to your SIEM to detect potential exploitation attempts.
• Monitor network traffic for unusual outbound connections originating from Ruby or Ruby on Rails application servers (see network connection rule below).