CVE-1999-1159 is a vulnerability affecting SSH version 2.0.11 and earlier, where local users are able to request remote port forwarding from privileged ports without requiring root privileges. Normally, binding to privileged ports (ports below 1024) requires elevated permissions to prevent unauthorized services from running on these ports. However, due to this flaw in SSH 2.0.11 and earlier, any local user can request remote forwarding from these privileged ports, potentially allowing them to redirect network traffic through the SSH server in an unauthorized manner. This can lead to unauthorized access or interception of network communications, as well as potential privilege escalation if the forwarded ports are used to access sensitive services. The vulnerability has a CVSS score of 4.6 (medium severity), indicating a moderate risk. The attack vector is local (AV:L), with low attack complexity (AC:L), no authentication required (Au:N), and impacts confidentiality, integrity, and availability (C:P/I:P/A:P). No patches are available for this vulnerability, and there are no known exploits in the wild. Given the age of the vulnerability (published in 1998) and the affected version being SSH 2.0.11 and earlier, modern SSH implementations are unlikely to be affected. However, legacy systems still running these versions remain vulnerable. The vulnerability primarily affects systems where local user accounts exist and SSH 2.0.11 or earlier is in use, allowing local users to leverage the remote forwarding feature to bind privileged ports remotely without proper authorization.

For European organizations, the impact of this vulnerability depends largely on the presence of legacy systems running SSH 2.0.11 or earlier. If such systems exist, local users (including potentially malicious insiders or compromised accounts) could exploit this vulnerability to redirect network traffic through privileged ports remotely, potentially bypassing network access controls or firewall rules. This could lead to unauthorized access to sensitive internal services, interception of confidential data, or disruption of service availability. The confidentiality, integrity, and availability of critical systems could be compromised. While the vulnerability requires local access, insider threats or attackers who have gained limited user access could leverage this flaw to escalate their capabilities. In environments with strict network segmentation and monitoring, this vulnerability could facilitate lateral movement or data exfiltration. However, given the age and limited scope of the vulnerability, the overall risk to modern European organizations is low unless legacy SSH versions are still in use on critical systems.

1. Upgrade SSH to a modern, supported version: The most effective mitigation is to upgrade all SSH servers and clients to current, patched versions that do not contain this vulnerability. 2. Audit and decommission legacy systems: Identify any systems still running SSH 2.0.11 or earlier and either upgrade or retire them from production environments. 3. Restrict local user access: Limit the number of local user accounts on SSH servers, especially on legacy systems, to reduce the risk of exploitation. 4. Disable remote port forwarding if not required: Configure SSH server settings to disable remote port forwarding globally or for specific users to prevent misuse. 5. Implement strict network segmentation and monitoring: Monitor SSH traffic and network connections for unusual port forwarding activity, especially from privileged ports, and enforce network segmentation to limit lateral movement. 6. Use host-based access controls: Employ tools like SELinux or AppArmor to restrict SSH daemon capabilities and prevent unauthorized port binding. 7. Regularly review SSH configuration files (sshd_config) to ensure secure settings and disable legacy or insecure features.