CVE-1999-0168 in SunOS
Summary
by MITRE
The portmapper may act as a proxy and redirect service requests from an attacker, making the request appear to come from the local host, possibly bypassing authentication that would otherwise have taken place. For example, NFS file systems could be mounted through the portmapper despite export restrictions.
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Analysis
by VulDB Data Team • 04/16/2026
The vulnerability described in CVE-1999-0168 represents a critical flaw in the portmapper service that operates within the network infrastructure of Unix-based systems and other platforms supporting the ONC RPC (Open Network Computing Remote Procedure Call) protocol. This weakness stems from the portmapper's design to act as a central registry that maps RPC program numbers to network ports, but it fails to properly validate the authenticity of incoming requests. The service essentially functions as a proxy mechanism that can be exploited to redirect service requests, creating a fundamental security gap in the authentication process that should normally prevent unauthorized access to network services.
The technical implementation of this vulnerability allows attackers to manipulate the portmapper into forwarding requests as if they originated from the local host system. This spoofing capability bypasses the normal authentication mechanisms that would typically validate the legitimacy of service requests before granting access to protected resources. When an attacker exploits this flaw, they can effectively masquerade as a local client and gain unauthorized access to services that would otherwise be restricted by the system's access control policies. The portmapper's proxy behavior creates a pathway through which malicious actors can circumvent network security controls and gain access to sensitive services without proper authorization.
The operational impact of this vulnerability extends beyond simple unauthorized access to encompass broader security implications for networked systems. NFS (Network File System) mounts represent a particularly dangerous scenario where attackers can exploit this weakness to access file systems that should be protected by export restrictions. The vulnerability undermines the fundamental security model of network services by allowing remote attackers to bypass local authentication mechanisms, potentially leading to data breaches, privilege escalation, and unauthorized system access. Systems running vulnerable portmapper implementations become susceptible to attacks that can compromise entire network infrastructures, as the flaw affects the core communication mechanisms that enable distributed services.
Organizations affected by this vulnerability should implement immediate mitigations including disabling unnecessary RPC services, configuring proper firewall rules to restrict access to portmapper ports, and ensuring that only trusted hosts can communicate with the portmapper service. The vulnerability aligns with CWE-284 (Improper Access Control) and represents a classic example of how proxy services can be exploited to bypass authentication mechanisms. From an ATT&CK framework perspective, this vulnerability maps to techniques involving proxy execution and privilege escalation, as attackers can leverage the portmapper to gain unauthorized access to protected resources. Network segmentation and the implementation of proper access controls for RPC services can effectively mitigate this risk, while regular security audits should verify that portmapper configurations do not expose unnecessary service access to external networks.