CVE-2020-7385 in Metasploit Framework
Summary
by MITRE • 04/24/2021
By launching the drb_remote_codeexec exploit, a Metasploit Framework user will inadvertently expose Metasploit to the same deserialization issue that is exploited by that module, due to the reliance on the vulnerable Distributed Ruby class functions. Since Metasploit Framework typically runs with elevated privileges, this can lead to a system compromise on the Metasploit workstation. Note that an attacker would have to lie in wait and entice the Metasploit user to run the affected module against a malicious endpoint in a "hack-back" type of attack. Metasploit is only vulnerable when the drb_remote_codeexec module is running. In most cases, this cannot happen automatically.
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Analysis
by VulDB Data Team • 04/29/2021
CVE-2020-7385 represents a critical deserialization vulnerability within the Metasploit Framework that exploits the Distributed Ruby (DRb) class functions to achieve remote code execution. This vulnerability operates through the drb_remote_codeexec exploit module, which creates a dangerous chain of execution where the Metasploit framework itself becomes compromised during the exploitation process. The flaw stems from the framework's reliance on vulnerable DRb functionality that handles remote object serialization and deserialization operations. When an attacker crafts a malicious payload and entices a Metasploit user to execute the affected module against a controlled endpoint, the framework's elevated privileges become weaponized for system compromise. The vulnerability is particularly concerning because Metasploit typically operates with elevated system privileges, making successful exploitation equivalent to full system compromise of the attacking workstation. This represents a classic privilege escalation scenario where the attacker leverages the legitimate tool's capabilities against itself.
The technical implementation of this vulnerability involves the manipulation of serialized Ruby objects through the DRb protocol, which is designed for remote method invocation and object sharing across networks. When Metasploit processes these maliciously crafted serialized objects, the deserialization process triggers arbitrary code execution within the framework's runtime environment. The attack vector requires social engineering or targeted deception since the vulnerability only activates when a user explicitly runs the vulnerable module against an attacker-controlled endpoint. This limitation prevents automatic exploitation but does not eliminate the threat, as the attack can still succeed through carefully orchestrated user interaction. The vulnerability falls under the broader category of deserialization flaws that are commonly classified as CWE-502 in the Common Weakness Enumeration catalog, specifically targeting insecure deserialization patterns that allow attackers to execute arbitrary code.
The operational impact of CVE-2020-7385 extends beyond simple remote code execution to encompass complete system compromise of the Metasploit workstation. Since Metasploit typically runs with administrative privileges, successful exploitation can provide attackers with full control over the attacking system, including access to network resources, file system operations, and potential lateral movement capabilities. The vulnerability's indirect nature means that attackers need to establish a waiting position and entice the target user to execute the malicious module, but this approach still represents a significant security risk in environments where Metasploit is frequently used for penetration testing. The attack scenario aligns with ATT&CK technique T1059.007 for command and scripting interpreter, as the exploitation results in arbitrary code execution through the Ruby runtime environment. The impact is particularly severe for security professionals who rely on Metasploit for legitimate penetration testing activities, as the tool that should be a defensive asset becomes a potential entry point for adversaries.
Mitigation strategies for CVE-2020-7385 focus on both immediate protective measures and long-term architectural improvements. The most effective immediate solution involves avoiding the use of the vulnerable drb_remote_codeexec module unless absolutely necessary, and when usage is required, ensuring that the target endpoints are trusted and secure. Users should implement strict access controls and network segmentation to limit exposure to potentially malicious endpoints. The vulnerability also highlights the importance of keeping Metasploit updated with the latest security patches, as the issue was resolved through proper serialization handling and input validation. Organizations should consider implementing network monitoring to detect unusual DRb traffic patterns and establish security awareness training to prevent social engineering attacks that could lead to exploitation. Additionally, the incident underscores the need for secure coding practices in framework development, particularly around serialization and deserialization operations, to prevent similar vulnerabilities from emerging in other components of the security toolchain. The vulnerability demonstrates the critical importance of validating external inputs and implementing proper sandboxing mechanisms when handling serialized data from untrusted sources, as recommended by industry best practices in secure software development.