CVE-2023-6004 is a vulnerability identified in the libssh component used within Red Hat Enterprise Linux 8. The flaw arises from improper neutralization of special elements in output that are subsequently used by downstream components, specifically within the ProxyCommand or ProxyJump SSH client features. These features allow users to specify commands or jump hosts to proxy SSH connections. The vulnerability is triggered when the hostname parameter is not properly sanitized, enabling an attacker to inject malicious code into the command executed by these features. Exploitation requires the attacker to have limited privileges (local access) and user interaction, such as convincing a user to connect to a malicious host or manipulate hostname input. The CVSS 3.1 base score is 4.8 (medium severity), reflecting low to moderate impact on confidentiality, integrity, and availability. The attack vector is local (AV:L), with low attack complexity (AC:L), requiring privileges (PR:L) and user interaction (UI:R). The vulnerability does not appear to be exploited in the wild yet. The root cause is insufficient input validation and sanitization of hostname syntax in libssh, which can lead to command injection in the ProxyCommand or ProxyJump execution context. This can allow an attacker to execute arbitrary commands with the privileges of the user running the SSH client, potentially leading to unauthorized actions or data exposure.

For European organizations, this vulnerability poses a moderate risk primarily to systems running Red Hat Enterprise Linux 8 that utilize SSH ProxyCommand or ProxyJump features. The potential impacts include unauthorized command execution, which could compromise system integrity and confidentiality, and potentially disrupt availability if malicious commands affect system processes. Organizations relying on SSH for secure remote access, automated scripts, or jump hosts are particularly vulnerable. Although exploitation requires local privileges and user interaction, the risk is heightened in environments with multiple users or where users connect to untrusted networks or hosts. Critical infrastructure sectors, government agencies, and enterprises with sensitive data or complex SSH configurations may face increased exposure. The absence of known exploits in the wild reduces immediate risk but does not eliminate the threat, especially as attackers may develop exploits over time. Failure to address this vulnerability could lead to lateral movement within networks or privilege escalation scenarios.

European organizations should apply the following specific mitigations: 1) Immediately update libssh and Red Hat Enterprise Linux 8 packages to the latest patched versions once available from Red Hat to eliminate the vulnerability. 2) Review and restrict the use of ProxyCommand and ProxyJump features, especially in automated scripts or user configurations, to minimize exposure. 3) Implement strict input validation and sanitization controls on hostname parameters in SSH client configurations to prevent injection attempts. 4) Educate users about the risks of connecting to untrusted hosts and the importance of verifying SSH configurations. 5) Employ monitoring and logging of SSH client activities, focusing on ProxyCommand and ProxyJump usage patterns to detect anomalous behavior. 6) Limit local user privileges and enforce the principle of least privilege to reduce the impact of potential exploitation. 7) Use network segmentation and access controls to restrict SSH client access to trusted hosts only. These measures go beyond generic patching and address the specific attack vector and exploitation conditions.