CVE-2018-20587 in Bitcoin Core
Summary
by MITRE
Bitcoin Core 0.12.0 through 0.17.1 and Bitcoin Knots 0.12.0 through 0.17.x before 0.17.1.knots20181229 have Incorrect Access Control. Local users can exploit this to steal currency by binding the RPC IPv4 localhost port, and forwarding requests to the IPv6 localhost port.
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Analysis
by VulDB Data Team • 07/09/2023
This vulnerability affects Bitcoin Core versions 0.12.0 through 0.17.1 and Bitcoin Knots versions 0.12.0 through 0.17.x before 0.17.1.knots20181229, representing a critical access control flaw that undermines the security of the Bitcoin network infrastructure. The issue stems from improper handling of IPv4 and IPv6 localhost port binding mechanisms within the RPC service implementation, creating a significant attack surface that allows local adversaries to bypass authentication controls and execute unauthorized transactions.
The technical flaw manifests when the Bitcoin daemon binds to the IPv4 localhost port while simultaneously allowing IPv6 connections to be forwarded to the same RPC service. This creates a scenario where a local attacker can establish a connection to the IPv4 localhost port and then craft malicious requests that are forwarded to the IPv6 localhost port, effectively circumventing the intended access controls. The vulnerability is classified as CWE-284 Access Control, specifically related to improper access control mechanisms in network services. This flaw allows attackers to exploit the RPC interface without proper authentication, potentially enabling them to perform operations such as sending transactions, viewing wallet information, or extracting private keys from the compromised node.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it represents a fundamental flaw in the network service architecture that could lead to complete compromise of Bitcoin nodes. Local attackers with minimal privileges can leverage this weakness to steal cryptocurrency from nodes that are improperly configured or have not been updated to patched versions. The attack vector requires only local system access, making it particularly dangerous for nodes running on shared systems or servers where unauthorized users might have access to the underlying operating system. This vulnerability directly aligns with ATT&CK technique T1068, which involves exploiting local system permissions, and T1071, covering application layer protocol usage, as the attack exploits the RPC communication protocol.
Mitigation strategies for this vulnerability require immediate patching of affected Bitcoin Core and Bitcoin Knots installations to versions that properly handle IPv4 and IPv6 localhost port binding. Administrators should also implement proper network configuration practices, including explicit binding to specific IP addresses rather than allowing automatic binding to all interfaces. Additional protective measures include configuring firewall rules to restrict RPC access to trusted networks, implementing proper authentication mechanisms, and regularly monitoring node logs for suspicious activity. The vulnerability underscores the importance of proper network service configuration and access control implementation in cryptocurrency infrastructure, particularly for services that handle sensitive financial operations. Organizations should also consider implementing network segmentation and monitoring solutions to detect and prevent unauthorized access attempts to RPC interfaces.