CVE-2025-37730 in Logstash
Summary
by MITRE • 05/06/2025
Improper certificate validation in Logstash's TCP output could lead to a man-in-the-middle (MitM) attack in “client” mode, as hostname verification in TCP output was not being performed when the ssl_verification_mode => full was set.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 05/06/2025
The vulnerability identified as CVE-2025-37730 represents a critical security flaw in Elastic Logstash's TCP output functionality that undermines the integrity of secure communications. This issue specifically affects Logstash instances operating in client mode where SSL/TLS encryption is intended to protect data transmission between systems. The flaw manifests when the ssl_verification_mode => full configuration parameter is set, which should normally enforce comprehensive certificate validation including hostname verification. However, the implementation fails to perform proper hostname validation, creating a significant gap in the security posture of affected systems.
The technical root cause of this vulnerability lies in the improper handling of SSL certificate validation within Logstash's TCP output plugin. When ssl_verification_mode => full is configured, the system should validate both the certificate's authenticity and its association with the target hostname to prevent attackers from intercepting communications. The absence of hostname verification means that Logstash will accept any certificate presented by a malicious actor during the SSL handshake process, regardless of whether it matches the intended destination server. This failure directly violates fundamental security principles of certificate-based authentication and creates an attack surface where adversaries can establish fraudulent connections without detection.
From an operational impact perspective, this vulnerability exposes organizations to significant man-in-the-middle attack risks that can compromise the confidentiality and integrity of log data flowing through their network infrastructure. Attackers positioned between the Logstash client and destination servers can intercept, modify, or redirect log traffic without being detected by the system's security controls. This threat is particularly concerning in environments where sensitive operational data, security events, or compliance-related logs are transmitted through the affected Logstash instances. The vulnerability essentially renders the SSL/TLS protection mechanisms ineffective, leaving organizations vulnerable to data breaches, information disclosure, and potential system compromise through log manipulation.
Organizations should immediately implement mitigations to address this vulnerability by ensuring that all Logstash instances using TCP output with SSL/TLS are properly configured with hostname verification enabled. The recommended approach involves verifying that the ssl_verification_mode => full setting actually enforces hostname validation, which may require patching the Logstash software to correct the implementation flaw. Additionally, network administrators should consider implementing additional monitoring controls to detect unusual connection patterns or certificate mismatches that might indicate successful MitM attacks. The vulnerability aligns with CWE-295 which specifically addresses improper certificate validation and relates to ATT&CK technique T1566.001 for credential access through the exploitation of weak certificate validation mechanisms. Organizations should also review their overall certificate management practices and consider implementing certificate pinning strategies as additional protective measures against this class of attack.
This vulnerability demonstrates the critical importance of proper SSL/TLS implementation in security tools and highlights the potential consequences when fundamental security controls are inadequately enforced. The flaw represents a failure in the security principle of defense in depth, where multiple layers of protection should work together to prevent unauthorized access. Organizations relying on Logstash for log aggregation and monitoring must prioritize this remediation to maintain the trustworthiness of their security infrastructure and prevent potential exploitation by threat actors targeting their network communications.