CVE-2015-5677 in FreeBSD
Summary
by MITRE
bsnmpd, as used in FreeBSD 9.3, 10.1, and 10.2, uses world-readable permissions on the snmpd.config file, which allows local users to obtain the secret key for USM authentication by reading the file.
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Analysis
by VulDB Data Team • 11/11/2022
The vulnerability identified as CVE-2015-5677 affects the bsnmpd daemon in FreeBSD versions 9.3, 10.1, and 10.2, representing a critical access control flaw that undermines the security of SNMP (Simple Network Management Protocol) implementations. This issue stems from improper file permission settings on the snmpd.config configuration file, which is used to store sensitive authentication credentials for SNMPv3 USM (User-based Security Model) operations. The flaw allows any local user on the system to read the configuration file and extract the secret key used for user-based authentication, effectively compromising the entire SNMP security framework. The root cause of this vulnerability aligns with CWE-732, which describes improper privilege management where security-critical information is accessible to unauthorized users due to inadequate file permissions. The bsnmpd daemon in affected FreeBSD versions fails to implement proper access controls for its configuration files, creating a significant attack surface that violates fundamental security principles of least privilege and proper resource protection.
The operational impact of this vulnerability extends beyond simple information disclosure, as it fundamentally compromises the integrity and confidentiality of SNMP communications within the affected systems. When local users can access the USM secret key through the world-readable snmpd.config file, they gain the ability to impersonate legitimate SNMP users and potentially execute unauthorized management operations. This creates opportunities for privilege escalation attacks where attackers can manipulate network device configurations, extract sensitive network information, or disrupt services through unauthorized SNMP commands. The vulnerability also enables persistent access patterns that could go undetected for extended periods, as the compromised secret key allows attackers to maintain control over SNMP-managed network infrastructure. From an attack framework perspective, this issue maps to multiple ATT&CK techniques including privilege escalation through access token manipulation and credential access through file and directory permissions.
The security implications of this vulnerability are particularly severe given that SNMPv3 USM authentication is designed to provide strong security assurances for network management communications. The exposure of the secret key effectively nullifies the cryptographic protections intended by the USM framework, rendering the authentication mechanism useless for its intended purpose. This flaw demonstrates a critical failure in the principle of least privilege, where sensitive configuration information that should be accessible only to the SNMP daemon process is made available to all local users. The vulnerability affects not just the immediate system but potentially the entire network infrastructure that relies on SNMP for management and monitoring purposes. Organizations using affected FreeBSD versions face significant risk of unauthorized network access and potential data breaches, as the compromised secret key could enable attackers to gain comprehensive visibility into network device configurations and operational status.
Mitigation strategies for CVE-2015-5677 should focus on immediate remediation through proper file permission configuration and system updates. The most direct solution involves setting restrictive permissions on the snmpd.config file to ensure that only the bsnmpd process and authorized administrators can access the sensitive configuration data. This can be achieved by changing file ownership to the appropriate user and implementing read/write permissions that exclude world access. System administrators should also consider implementing additional security controls such as mandatory access controls, file integrity monitoring, and regular security audits to detect similar permission misconfigurations. The FreeBSD security team addressed this issue in subsequent releases by correcting the default file permissions for SNMP configuration files. Organizations should also implement network segmentation and monitoring to detect unauthorized SNMP access attempts and consider migrating to more secure SNMP implementations where possible. The vulnerability underscores the importance of regular security assessments and proper configuration management practices to prevent similar issues in other system components.