CVE-2020-16248 in Blackbox Exporter
Summary
by MITRE
** DISPUTED ** Prometheus Blackbox Exporter through 0.17.0 allows /probe?target= SSRF. NOTE: follow-on discussion suggests that this might plausibly be interpreted as both intended functionality and also a vulnerability.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 08/04/2024
The CVE-2020-16248 vulnerability affects the Prometheus Blackbox Exporter version 0.17.0 and earlier, presenting a Server-Side Request Forgery (SSRF) condition through the /probe endpoint when the target parameter is manipulated. This vulnerability exists within the exporter's handling of external probe requests, where the application fails to properly validate or sanitize input parameters before using them to make HTTP requests to target systems. The issue manifests when an attacker can manipulate the target parameter to cause the exporter to make requests to internal systems or resources that should not be accessible through the public interface. The vulnerability's disputed nature stems from the ambiguity of whether this behavior constitutes intended functionality or represents a security flaw, as the Blackbox Exporter is designed to probe external targets, but the lack of proper input validation creates opportunities for unintended access to internal resources. This vulnerability directly relates to CWE-918, which describes Server-Side Request Forgery vulnerabilities where applications use untrusted input to construct HTTP requests to remote resources without proper validation. The operational impact of this vulnerability is significant as it could allow attackers to perform reconnaissance on internal network resources, access sensitive data, or potentially escalate privileges by reaching internal services that are not meant to be exposed to external probing. Attackers could leverage this vulnerability to bypass network segmentation controls and gain access to internal systems that would normally be protected by firewalls or other network security controls. The Blackbox Exporter's design intent is to probe external targets, but when combined with insufficient input validation, it can be exploited to probe internal systems that are not intended to be accessible through the exporter's interface. This vulnerability aligns with ATT&CK technique T1106, which describes the use of remote services to access internal systems, and could be exploited as part of a broader attack chain to establish persistence or escalate privileges within a network. The vulnerability's classification as disputed reflects the complexity of determining whether the behavior is a legitimate feature or an exploitable weakness, as the exporter's functionality inherently involves making external requests but the lack of proper validation creates security implications.
The technical flaw in CVE-2020-16248 resides in the Blackbox Exporter's insufficient input validation mechanisms when processing the target parameter in the /probe endpoint. The application accepts user-supplied input without proper sanitization or validation, allowing malicious actors to manipulate the target parameter to include internal IP addresses, localhost references, or other internal resources. This lack of input validation creates a direct path for attackers to force the exporter to make HTTP requests to internal systems that should remain isolated from external access. The vulnerability occurs because the exporter does not properly restrict or validate the URLs or IP addresses provided in the target parameter, enabling attackers to craft requests that bypass normal network access controls. This flaw essentially allows an attacker to use the exporter as a proxy to make requests to internal resources, effectively circumventing network security controls that would normally prevent such access. The vulnerability's impact is amplified by the fact that the Blackbox Exporter typically runs with elevated privileges or access to internal network resources, making any successful exploitation potentially more dangerous. The issue demonstrates a classic lack of proper access control and input validation, where the application fails to implement proper boundary checks before using user-provided data to initiate network communications. This vulnerability represents a failure to implement proper defense-in-depth principles where multiple layers of security controls should prevent unauthorized access to internal resources through external interfaces. The Blackbox Exporter's architecture creates an inherent risk when it processes external input that can be directed to internal systems without proper validation or access controls.
The operational impact of CVE-2020-16248 extends beyond simple information disclosure to potentially enable more sophisticated attacks within a compromised environment. When exploited, this vulnerability allows attackers to perform internal network reconnaissance by probing internal services that would normally be protected from external access. The attacker could use the exporter to map internal network topology, identify running services, and potentially discover vulnerable internal systems that are not exposed to the public internet. This reconnaissance capability can significantly aid in planning further attacks and establishing persistence within the network. The vulnerability could also enable attackers to access internal APIs or services that contain sensitive data, potentially leading to data breaches or privilege escalation. Additionally, the vulnerability could be exploited to perform denial-of-service attacks against internal systems by forcing the exporter to make excessive requests to internal resources. The Blackbox Exporter's role in monitoring external systems makes it an attractive target for attackers who wish to maintain persistent access to internal networks while appearing to be legitimate monitoring traffic. The disputed nature of this vulnerability means that organizations must carefully evaluate their specific deployment scenarios and determine whether the functionality constitutes acceptable risk or requires additional mitigation measures. The impact is particularly concerning in environments where the Blackbox Exporter is deployed with access to internal network resources or where it operates in a context that provides elevated privileges. Organizations may need to implement additional network segmentation or access controls to prevent exploitation of this vulnerability.
Mitigation strategies for CVE-2020-16248 should focus on implementing proper input validation and access control measures to prevent unauthorized access to internal resources through the Blackbox Exporter. The most effective approach involves upgrading to a version of the Blackbox Exporter that addresses this vulnerability through proper input validation and sanitization. Organizations should also implement network segmentation controls that prevent the exporter from accessing internal resources that should remain isolated from external probing. The implementation of proper access controls and firewall rules can help limit the potential impact of this vulnerability by restricting what internal resources the exporter can access. Additionally, organizations should consider implementing network monitoring and anomaly detection systems to identify unusual patterns of traffic that may indicate exploitation attempts. The use of dedicated network zones or virtual private clouds for monitoring systems can help contain the potential impact of such vulnerabilities. Organizations should also implement proper logging and monitoring of exporter activities to detect potential exploitation attempts and maintain audit trails of all probe activities. Security hardening measures such as disabling unnecessary features, implementing least privilege access controls, and regularly updating the exporter to the latest secure versions should be implemented. The vulnerability's disputed nature means that organizations should carefully review their specific use cases and determine whether additional controls are necessary to prevent exploitation, particularly in environments where internal access is not properly restricted. Proper security awareness training for administrators who manage monitoring systems can help prevent accidental configuration issues that might increase the attack surface. The implementation of these mitigation measures should align with security frameworks such as NIST SP 800-53 controls for access control and system and information integrity to ensure comprehensive protection against this and similar vulnerabilities.