CVE-2019-16546 in Google Compute Engine Plugin
Summary
by MITRE
Jenkins Google Compute Engine Plugin 4.1.1 and earlier does not verify SSH host keys when connecting agents created by the plugin, enabling man-in-the-middle attacks.
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Analysis
by VulDB Data Team • 11/22/2019
The vulnerability identified as CVE-2019-16546 resides within the Jenkins Google Compute Engine Plugin version 4.1.1 and earlier, presenting a critical security risk that undermines the integrity of agent connections within cloud-based CI/CD environments. This flaw specifically affects the plugin's handling of SSH connections between Jenkins master and dynamically provisioned compute agents, creating an exploitable gap in the authentication process that adversaries can leverage to compromise the entire build infrastructure.
The technical root cause of this vulnerability stems from the plugin's failure to implement proper SSH host key verification during the connection establishment phase. When Jenkins creates compute agents through the Google Compute Engine plugin, it establishes SSH connections to these agents to execute build tasks. However, the plugin does not validate the SSH host keys presented by the remote agents against known good keys, allowing attackers to intercept and manipulate these connections. This missing verification step creates a man-in-the-middle attack vector where malicious actors can position themselves between the Jenkins master and the compute agents, potentially gaining access to build artifacts, credentials, and execution commands.
The operational impact of this vulnerability extends beyond simple network interception, as it fundamentally compromises the trust model of Jenkins-based continuous integration systems. Attackers who successfully exploit this vulnerability can execute arbitrary code on build agents, potentially gaining access to sensitive source code repositories, build credentials, and other confidential information. The implications are particularly severe in enterprise environments where Jenkins serves as the central hub for software delivery pipelines, as compromised agents can lead to supply chain attacks, credential theft, and unauthorized code deployments. This vulnerability also undermines the security posture of organizations relying on cloud-based CI/CD infrastructure, as it allows attackers to establish persistent access points within the build environment.
Security professionals should recognize this vulnerability as a clear example of CWE-310, which addresses cryptographic weaknesses in host key validation, and aligns with ATT&CK technique T1566, focusing on credential harvesting through man-in-the-middle attacks. Organizations should immediately upgrade to Jenkins Google Compute Engine Plugin version 4.1.2 or later, which implements proper SSH host key verification mechanisms. Additional mitigations include implementing network-level controls such as firewall rules that restrict access to compute agents, configuring Jenkins with explicit SSH known hosts files, and establishing monitoring for unusual connection patterns. The vulnerability also highlights the importance of proper key management practices and the necessity of validating all cryptographic assertions in distributed systems, particularly those involving cloud infrastructure integration where trust boundaries are inherently more complex than traditional network environments.