CVE-2006-2655 in FreeBSD
Summary
by MITRE
The build process for ypserv in FreeBSD 5.3 up to 6.1 accidentally disables access restrictions when using the /var/yp/securenets file, which allows remote attackers to bypass intended access restrictions.
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Analysis
by VulDB Data Team • 03/13/2021
The vulnerability described in CVE-2006-2655 affects the ypserv package in FreeBSD versions 5.3 through 6.1, representing a critical access control flaw in the NIS (Network Information Service) implementation. This issue specifically impacts the build process of ypserv where the security restrictions intended to be enforced through the /var/yp/securenets file are inadvertently disabled during compilation. The ypserv service is responsible for providing network-wide access to user and system information, making it a critical component in enterprise environments where network services must be tightly controlled. The flaw stems from improper handling of security parameters during the software compilation phase, creating a scenario where legitimate access controls are bypassed without explicit configuration changes.
The technical root cause of this vulnerability lies in the build-time processing of security configurations within the ypserv package. When the software is compiled on affected FreeBSD versions, the build process fails to properly incorporate access restriction settings from the /var/yp/securenets file, effectively rendering these security controls ineffective. This represents a classic case of insecure configuration management during software compilation, where the security posture of the final binary is compromised by flawed build-time logic. The vulnerability is particularly dangerous because it operates at the compilation level rather than at runtime, meaning that even if administrators properly configure the securenets file, the compiled binary ignores these settings. This flaw aligns with CWE-254, which addresses weaknesses in security features due to improper implementation during the software development lifecycle.
The operational impact of this vulnerability is severe for any FreeBSD systems running affected ypserv versions, as it creates an unauthorized access vector that could allow remote attackers to bypass network security controls. Attackers exploiting this vulnerability could gain access to sensitive network information that should be restricted to authorized hosts only, potentially leading to privilege escalation, lateral movement, or information disclosure within the network. The vulnerability is particularly concerning in enterprise environments where NIS is commonly used for centralized user and system management, as it undermines the fundamental security assumptions of networked services. The attack surface expands beyond simple network access, as compromised NIS services can provide attackers with detailed information about user accounts, system configurations, and network topology that can be leveraged for further attacks. This vulnerability directly relates to ATT&CK technique T1078 which covers valid accounts and T1566 which involves credential harvesting through network services.
Mitigation strategies for this vulnerability require immediate system updates to patched FreeBSD versions where the build process has been corrected to properly respect security configurations. Administrators should verify that their systems are running patched versions of FreeBSD and that the ypserv package has been rebuilt with proper access control enforcement. The recommended approach includes applying the relevant FreeBSD security advisories and rebuilding the ypserv package from source to ensure that access restrictions from /var/yp/securenets are properly enforced. Additional defensive measures include monitoring network traffic for unauthorized access attempts to NIS services, implementing network segmentation to limit access to NIS servers, and considering the deprecation of NIS in favor of more modern authentication and directory services. Organizations should also conduct thorough audits of their network security configurations to identify any other services that might be affected by similar build-time security flaws, as this vulnerability demonstrates the importance of proper security controls during software compilation phases.