CVE-2012-0862 in Xinetd
Summary
by MITRE
builtins.c in Xinetd before 2.3.15 does not check the service type when the tcpmux-server service is enabled, which exposes all enabled services and allows remote attackers to bypass intended access restrictions via a request to tcpmux port 1.
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Analysis
by VulDB Data Team • 12/03/2021
The vulnerability described in CVE-2012-0862 resides within the xinetd daemon version 2.3.14 and earlier, specifically in the builtins.c file where inadequate service type validation occurs when the tcpmux-server service is enabled. This flaw represents a critical access control bypass vulnerability that fundamentally undermines the security model of the xinetd service management system. The tcpmux protocol serves as a service multiplexer that traditionally listens on port 1 and is designed to route incoming connections to appropriate services based on the requested service name. When xinetd operates with tcpmux-server enabled, it fails to validate whether the requested service type matches the expected protocol, creating a pathway for attackers to bypass intended access restrictions.
The technical flaw manifests in the improper handling of service type verification within the xinetd daemon's built-in service management functions. When tcpmux-server is enabled, the daemon does not properly validate the service type associated with incoming requests to port 1, allowing attackers to submit requests for any enabled service regardless of the intended access controls. This vulnerability is classified under CWE-284 Access Control Bypass, which specifically addresses situations where improper access control mechanisms allow unauthorized access to protected resources. The flaw directly violates the principle of least privilege and represents a failure in the authorization mechanism that should prevent unauthorized service access.
The operational impact of this vulnerability is severe as it enables remote attackers to gain access to services that should be restricted or protected. An attacker can exploit this vulnerability by simply connecting to port 1 and requesting access to any service that is enabled in the xinetd configuration, effectively bypassing all intended access restrictions. This creates a significant risk for systems where xinetd manages multiple services with varying security requirements, as a single vulnerability in the tcpmux handling code can compromise the entire service portfolio. The attack vector is particularly dangerous because it requires minimal privileges and can be executed remotely without prior authentication, making it a prime target for automated exploitation tools.
The vulnerability aligns with several ATT&CK techniques including T1071.004 Application Layer Protocol: DNS and T1046 Network Service Scanning, as attackers can use the tcpmux service to enumerate and access other services on the network. Organizations running vulnerable versions of xinetd are exposed to potential lateral movement and privilege escalation attacks, as the compromised tcpmux service can serve as a gateway to other systems or services within the network infrastructure. The impact extends beyond simple unauthorized access, as this vulnerability can facilitate more complex attack chains including information gathering, service disruption, and potentially full system compromise depending on the services that are exposed through this bypass mechanism.
Mitigation strategies for this vulnerability require immediate patching of xinetd to version 2.3.15 or later, which contains the necessary fixes to properly validate service types when tcpmux-server is enabled. Organizations should also implement network segmentation and access control measures to limit exposure of xinetd services to unauthorized networks, while disabling tcpmux-server functionality if it is not required for business operations. Additionally, regular security audits should verify that xinetd configurations properly restrict service access and that unnecessary services are disabled to reduce the attack surface. The fix addresses the underlying CWE-284 issue by implementing proper access control validation and ensuring that service type checking occurs before granting access to protected resources.