Source: cve@mitre.org
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.
Attackers can exploit the portmapper service to bypass access controls and gain unauthorized access to network resources, such as mounting restricted NFS file systems. This vulnerability allows attackers to act as a proxy, making their requests appear to originate from the local host, effectively circumventing authentication and authorization mechanisms. Successful exploitation can lead to data exfiltration, system compromise, and denial-of-service.
Step 1: Target Identification: The attacker identifies a vulnerable system running the portmapper service (rpcbind or portmap). The attacker will likely use port scanning tools like Nmap to identify open ports, specifically port 111 (TCP and UDP), which is the default port for portmapper.
Step 2: Service Request Crafting: The attacker crafts a malicious service request, typically targeting a service like NFS (Network File System). This request is designed to be forwarded by the portmapper.
Step 3: Portmapper Proxying: The attacker sends the crafted request to the portmapper. The portmapper, acting as a proxy, forwards the request to the target service (e.g., the NFS server). The portmapper rewrites the source IP address of the request to appear as if it originated from the local host.
Step 4: Access Control Bypass: The target service (NFS server) receives the request, which now appears to originate from the local host. Because the request appears to be local, it bypasses any access control restrictions (e.g., export restrictions) that are based on the source IP address.
Step 5: Unauthorized Access: The target service grants access to the attacker, allowing them to mount restricted file systems, read sensitive data, or potentially execute arbitrary commands.
The vulnerability stems from the portmapper's design as a proxy for service requests. Specifically, the portmapper doesn't adequately validate the source of service requests, allowing an attacker to craft requests that appear to originate from the local host. This bypasses access control lists (ACLs) and other authentication mechanisms that rely on source IP address verification. The flaw lies in the lack of robust input validation and authorization checks when forwarding service requests. The portmapper trusts the client's reported source address, allowing an attacker to spoof their origin. This trust, combined with the proxy functionality, enables the attacker to effectively 'masquerade' as a legitimate user or system on the local network.
While no specific APTs are directly linked to this CVE, the nature of the vulnerability makes it attractive to any attacker seeking to gain unauthorized access to a network. This vulnerability is a classic example of a privilege escalation vulnerability. Not listed on CISA KEV.
Network traffic analysis: Monitor for unusual RPC traffic on port 111 (TCP and UDP).
Log analysis: Review system logs (e.g., syslog) for suspicious activity related to NFS mounts or other services registered with the portmapper.
Intrusion Detection Systems (IDS): Deploy IDS rules to detect anomalous RPC requests or attempts to access restricted resources via the portmapper.
File Integrity Monitoring: Monitor changes to critical system files, especially those related to NFS exports.
Vulnerability Scanners: Utilize vulnerability scanners (e.g., Nessus, OpenVAS) to identify systems running vulnerable versions of portmapper.
Disable the portmapper service if it is not required. This is the most effective mitigation.
If the portmapper is required, restrict access to it using firewall rules. Only allow access from trusted hosts.
Upgrade to a more secure RPC implementation (e.g., using a more modern RPC library).
Implement strong access controls on services that rely on the portmapper, such as NFS. Use Kerberos or other authentication mechanisms that are not solely based on IP address.
Regularly audit and review system configurations, including NFS exports and portmapper settings.
Implement network segmentation to limit the impact of a successful exploit.