CVE-2020-15136 in ectd
Summary
by MITRE
In ectd before versions 3.4.10 and 3.3.23, gateway TLS authentication is only applied to endpoints detected in DNS SRV records. When starting a gateway, TLS authentication will only be attempted on endpoints identified in DNS SRV records for a given domain, which occurs in the discoverEndpoints function. No authentication is performed against endpoints provided in the --endpoints flag. This has been fixed in versions 3.4.10 and 3.3.23 with improved documentation and deprecation of the functionality.
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Analysis
by VulDB Data Team • 11/07/2020
The vulnerability described in CVE-2020-15136 affects the etcd distributed key-value store system, specifically impacting the gateway component's TLS authentication mechanism. This issue represents a significant security weakness in the system's network communication security model where authentication controls are selectively applied based on endpoint discovery methods rather than implementing comprehensive security policies across all configured endpoints.
The technical flaw manifests in the gateway's endpoint discovery process where the system only applies TLS authentication to endpoints identified through DNS SRV record resolution. When etcd gateway initializes, it calls the discoverEndpoints function which retrieves target endpoints from DNS SRV records but fails to enforce TLS authentication requirements for endpoints explicitly configured through the --endpoints command-line flag. This selective authentication approach creates a security gap where endpoints specified directly in the configuration remain unauthenticated, potentially allowing unauthorized access to the etcd cluster through these bypassed communication paths.
The operational impact of this vulnerability is substantial as it undermines the fundamental security assumptions of the etcd gateway's TLS protection mechanism. Attackers could exploit this weakness by configuring malicious endpoints through the --endpoints flag, bypassing the authentication checks that should normally protect cluster communications. This vulnerability directly relates to CWE-310, which addresses cryptographic weaknesses in authentication mechanisms, and aligns with ATT&CK technique T1071.004 for application layer protocol tunneling. The security gap effectively allows for potential man-in-the-middle attacks or unauthorized access to etcd cluster data where the gateway serves as an intermediary between clients and the actual etcd servers.
The fix implemented in versions 3.4.10 and 3.3.23 addresses this issue through improved documentation and the deprecation of the vulnerable functionality. This remediation approach reflects a security best practice of eliminating problematic features rather than attempting to patch their weaknesses. The deprecation process ensures that administrators must explicitly migrate to secure alternatives, reducing the risk of continued use of insecure configurations. Organizations should prioritize updating to these fixed versions and reviewing their gateway configurations to ensure all endpoints are properly authenticated, as the vulnerability represents a critical weakness in the system's network security posture that could lead to unauthorized access to sensitive distributed data.