CVE-2019-8336 in Consul
Summary
by MITRE
HashiCorp Consul (and Consul Enterprise) 1.4.x before 1.4.3 allows a client to bypass intended access restrictions and obtain the privileges of one other arbitrary token within secondary datacenters, because a token with literally "<hidden>" as its secret is used in unusual circumstances.
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Analysis
by VulDB Data Team • 07/26/2023
HashiCorp Consul versions 1.4.x prior to 1.4.3 contained a critical access control vulnerability that allowed unauthorized clients to escalate privileges and obtain the privileges of arbitrary tokens within secondary datacenters. This vulnerability stems from the improper handling of authentication tokens in cross-datacenter communication scenarios, specifically when a token with the literal secret value "<hidden>" is used in unusual circumstances. The flaw represents a significant bypass of intended security controls that could enable attackers to gain unauthorized access to sensitive data and operations across distributed Consul deployments.
The technical implementation of this vulnerability occurs within Consul's cross-datacenter replication and authentication mechanisms. When Consul operates across multiple datacenters, it requires secure token handling to maintain isolation between different deployment zones. The "<hidden>" token value represents a special case where the system fails to properly validate or sanitize authentication credentials during cross-datacenter operations. This creates a scenario where a client can manipulate the authentication flow to effectively impersonate other users or services within the secondary datacenter, thereby gaining access to resources that should be restricted to specific authorized entities.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass complete compromise of distributed service discovery and configuration management capabilities. An attacker exploiting this vulnerability could access sensitive service registrations, configuration data, and security policies across multiple datacenters, potentially leading to unauthorized service manipulation, data exfiltration, and disruption of critical infrastructure services. The vulnerability affects both Consul Community Edition and Consul Enterprise deployments, making it particularly concerning for organizations relying on HashiCorp's service mesh solutions for mission-critical operations.
This vulnerability aligns with CWE-285: Improper Authorization and CWE-306: Missing Authentication for Critical Function, as it represents a failure in proper access control enforcement and authentication mechanisms. From an ATT&CK framework perspective, this vulnerability maps to T1078: Valid Accounts and T1566: Phishing, as it enables attackers to leverage legitimate authentication tokens to gain unauthorized access to additional resources. Organizations should immediately upgrade to Consul version 1.4.3 or later to address this vulnerability, while also implementing additional monitoring for unusual authentication patterns and cross-datacenter token usage. Network segmentation and strict access controls should be maintained to limit the potential impact of any successful exploitation attempts.
The root cause of this issue lies in the inconsistent handling of special token values during cross-datacenter operations, where the system's validation logic fails to properly account for the "<hidden>" token case. This creates an authentication bypass scenario where the system accepts the token without proper verification, allowing attackers to proceed with operations as if they possessed legitimate credentials for other users or services. The vulnerability demonstrates the importance of comprehensive testing for edge cases in authentication systems and proper validation of all token handling scenarios, particularly in distributed systems where cross-zone communication introduces additional complexity to security controls.