CVE-2023-6004 is a vulnerability identified in libssh, a widely used SSH library, affecting Red Hat Enterprise Linux 8. The flaw arises from improper neutralization of special elements in output that are subsequently processed by downstream components, specifically when using the ProxyCommand or ProxyJump features of SSH. These features allow users to specify commands or jump hosts to proxy SSH connections. The vulnerability stems from unchecked hostname syntax in these features, which can be manipulated by an attacker to inject malicious code into the command executed by ProxyCommand or ProxyJump. Exploitation requires the attacker to have limited privileges (local access with some rights) and user interaction, such as convincing a user to connect to a malicious host or supply a crafted hostname. The impact includes potential injection of arbitrary commands, which can lead to partial compromise of confidentiality, integrity, and availability of the affected system. The CVSS 3.1 base score is 4.8 (medium), reflecting the need for local privileges and user interaction, as well as limited impact scope. No known exploits have been reported in the wild as of the publication date. The vulnerability highlights the risks associated with insufficient input validation in SSH client features that handle complex command execution flows. Organizations using RHEL 8 with libssh should monitor for patches and consider restricting or auditing the use of ProxyCommand and ProxyJump to mitigate risk.

For European organizations, the vulnerability poses a moderate risk primarily to systems running Red Hat Enterprise Linux 8 that utilize SSH ProxyCommand or ProxyJump features. Exploitation could allow attackers with limited local privileges to inject malicious commands, potentially leading to unauthorized command execution, data leakage, or service disruption. This could affect enterprise servers, development environments, and critical infrastructure systems relying on secure SSH connections. The requirement for user interaction and local privileges reduces the likelihood of widespread automated exploitation but does not eliminate targeted attacks, especially in environments with less stringent access controls. Confidentiality, integrity, and availability could be partially compromised, impacting business operations, data security, and compliance with European data protection regulations. Organizations in sectors such as finance, government, telecommunications, and energy, which often deploy RHEL 8 in critical roles, may face higher operational risks if this vulnerability is exploited.

1. Apply official patches from Red Hat as soon as they become available to address the vulnerability in libssh. 2. Until patches are applied, restrict or disable the use of ProxyCommand and ProxyJump features in SSH client configurations where feasible. 3. Implement strict input validation and sanitization for any hostname parameters used in ProxyCommand or ProxyJump to prevent injection of malicious code. 4. Enforce least privilege principles to limit local user permissions, reducing the potential for exploitation by low-privileged users. 5. Educate users about the risks of connecting to untrusted hosts or using unverified SSH configurations that may trigger this vulnerability. 6. Monitor SSH logs and system behavior for unusual command executions or proxy usage patterns indicative of exploitation attempts. 7. Employ endpoint detection and response (EDR) tools to detect suspicious activities related to SSH command injections. 8. Review and harden SSH client configurations across the organization, ensuring that only necessary features are enabled and properly secured.