CVE-2019-5645 in Metasploit Framework
Summary
by MITRE
By sending a specially crafted HTTP GET request to a listening Rapid7 Metasploit HTTP handler, an attacker can register an arbitrary regular expression. When evaluated, this malicious handler can either prevent new HTTP handler sessions from being established, or cause a resource exhaustion on the Metasploit server.
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Analysis
by VulDB Data Team • 11/12/2020
The vulnerability identified as CVE-2019-5645 represents a critical security flaw within the Rapid7 Metasploit framework's HTTP handler implementation. This vulnerability stems from inadequate input validation and sanitization mechanisms within the Metasploit HTTP service, which allows remote attackers to manipulate the regular expression evaluation process through crafted HTTP GET requests. The flaw exists specifically within the Metasploit framework's web-based exploit delivery mechanisms, where the HTTP handler component is responsible for managing incoming connections and session establishment. When an attacker submits a maliciously constructed HTTP GET request, the system processes this input without proper validation, enabling arbitrary regular expression registration within the handler's evaluation context.
The technical exploitation of this vulnerability occurs through the manipulation of the HTTP handler's regular expression processing capabilities, which falls under the category of improper input validation as classified by CWE-20. The attacker can craft a request that registers a malicious regular expression pattern, which when evaluated by the Metasploit server's HTTP handler, creates a denial of service condition or resource exhaustion scenario. This vulnerability operates at the application layer and affects the Metasploit framework's ability to properly manage concurrent HTTP sessions and resource allocation. The flaw specifically targets the Metasploit HTTP handler's session management system, where regular expression patterns are used to match and process incoming requests, creating a pathway for attackers to disrupt normal service operations.
The operational impact of CVE-2019-5645 extends beyond simple service disruption to encompass potential complete system compromise and resource exhaustion. An attacker can leverage this vulnerability to either prevent legitimate users from establishing new HTTP handler sessions, effectively creating a denial of service condition that blocks legitimate exploit delivery operations. Alternatively, the malicious regular expression can be crafted to consume excessive computational resources during evaluation, leading to resource exhaustion that can bring the entire Metasploit server to its knees. This vulnerability directly impacts the availability and integrity of Metasploit-based penetration testing operations, potentially compromising the security assessment process and allowing attackers to disrupt legitimate security testing activities. The impact is particularly severe in environments where Metasploit is used for continuous security testing or where the framework serves as a critical component in automated security tooling.
Mitigation strategies for CVE-2019-5645 should focus on implementing proper input validation and sanitization mechanisms within the Metasploit HTTP handler component. Organizations should immediately apply the vendor-provided security patches and updates to address this vulnerability. Network segmentation and access control measures can help limit exposure by restricting direct access to Metasploit HTTP handler endpoints. Implementing rate limiting and connection throttling mechanisms can help prevent abuse of the HTTP handler functionality. Additionally, monitoring for unusual patterns in HTTP GET requests and implementing intrusion detection systems can help identify exploitation attempts. The vulnerability demonstrates the importance of proper regular expression handling and input validation in security tools, aligning with ATT&CK technique T1499.004 for network denial of service and T1566.001 for spearphishing with malicious attachments. Organizations should also consider implementing application-level firewalls and web application firewalls to filter malicious HTTP requests before they reach the Metasploit framework. Regular security assessments and vulnerability scanning should include verification of patched versions to ensure complete remediation of this vulnerability.