CVE-2020-9487 in NiFi
Summary
by MITRE • 10/04/2020
In Apache NiFi 1.0.0 to 1.11.4, the NiFi download token (one-time password) mechanism used a fixed cache size and did not authenticate a request to create a download token, only when attempting to use the token to access the content. An unauthenticated user could repeatedly request download tokens, preventing legitimate users from requesting download tokens.
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Analysis
by VulDB Data Team • 11/15/2020
The vulnerability identified as CVE-2020-9487 affects Apache NiFi versions ranging from 1.0.0 through 1.11.4 and represents a significant authentication and access control weakness within the system's download token mechanism. This flaw resides in the token-based access control system that NiFi employs for managing content downloads, creating a scenario where unauthorized users can exploit the system's resource allocation process. The vulnerability specifically targets the token generation and validation workflow, where the system fails to properly authenticate requests during the token creation phase, allowing for potential abuse of the token generation mechanism. This represents a classic case of insufficient authentication controls and inadequate rate limiting or resource management within the access control system.
The technical implementation of this vulnerability stems from the fixed cache size configuration used in the download token system, combined with the absence of proper authentication checks during token generation requests. When an unauthenticated user submits a request for a download token, the system does not validate the requester's credentials or authorization status before creating and caching the token. This design flaw allows malicious actors to continuously generate tokens without proper authentication, leading to a resource exhaustion scenario where legitimate users cannot obtain tokens due to the cache being filled with unauthorized requests. The system's failure to implement proper request validation during token creation directly violates fundamental security principles of least privilege and proper access control enforcement. The vulnerability operates at the application layer and can be classified under CWE-305 Authentication Bypass Through User Identification, specifically manifesting as a weakness in the token generation process that lacks proper authentication mechanisms.
The operational impact of this vulnerability extends beyond simple denial of service conditions, as it creates a persistent threat to the availability and integrity of NiFi's content access controls. Legitimate users attempting to download content may find themselves unable to obtain download tokens due to the cache exhaustion caused by unauthorized token requests, effectively blocking legitimate access to system resources. This creates a cascading effect where authorized users cannot perform their intended operations, potentially disrupting critical workflows and data access processes within the NiFi environment. The vulnerability also represents a potential vector for amplification attacks, where attackers can systematically consume system resources to prevent legitimate operations. From an attack perspective, this weakness can be leveraged as part of broader exploitation campaigns targeting NiFi environments, potentially enabling further attacks through access to sensitive content or system information. The attack pattern aligns with techniques described in the ATT&CK framework under T1499-Endpoint Denial of Service, where adversaries consume system resources to prevent legitimate use of services.
Mitigation strategies for CVE-2020-9487 should focus on implementing proper authentication controls during token generation, establishing rate limiting mechanisms, and configuring appropriate cache management policies. Organizations should upgrade to Apache NiFi versions 1.12.0 or later where this vulnerability has been addressed through improved authentication checks and more robust resource management. Additional defensive measures include implementing proper access controls for token generation endpoints, adding request rate limiting to prevent abuse of the token creation mechanism, and monitoring for unusual patterns of token requests that may indicate malicious activity. Network-level controls such as firewalls and intrusion detection systems can also be configured to detect and block excessive token generation requests. The implementation of these mitigations should follow security best practices outlined in NIST SP 800-53 and ISO/IEC 27001 standards, particularly focusing on access control and resource management controls. Regular security audits and monitoring of token generation activities should be implemented to detect potential exploitation attempts and ensure the effectiveness of implemented controls.