CVE-2008-6123 in Net Snmp
Summary
by MITRE
The netsnmp_udp_fmtaddr function (snmplib/snmpUDPDomain.c) in net-snmp 5.0.9 through 5.4.2.1, when using TCP wrappers for client authorization, does not properly parse hosts.allow rules, which allows remote attackers to bypass intended access restrictions and execute SNMP queries, related to "source/destination IP address confusion."
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Analysis
by VulDB Data Team • 08/31/2019
The vulnerability identified as CVE-2008-6123 affects the net-snmp software suite version 5.0.9 through 5.4.2.1, specifically within the netsnmp_udp_fmtaddr function located in snmplib/snmpUDPDomain.c. This flaw represents a critical authorization bypass issue that undermines the security controls implemented through TCP wrappers for client access control. The vulnerability stems from improper parsing of hosts.allow rules, which are fundamental components of Unix-based network security mechanisms designed to control access to network services based on IP address criteria.
The technical root cause of this vulnerability lies in the function's inability to correctly interpret and validate source and destination IP address information when processing access control rules. When net-snmp utilizes TCP wrappers for authorization, the system should properly distinguish between source IP addresses (the originating client) and destination IP addresses (the server receiving the request). However, the netsnmp_udp_fmtaddr function fails to maintain this distinction, leading to a scenario where malicious actors can manipulate their network requests to appear as if they originate from authorized IP addresses. This confusion between source and destination addresses creates a pathway for unauthorized access to SNMP services that would otherwise be restricted.
The operational impact of this vulnerability is significant as it allows remote attackers to bypass intended access restrictions without requiring authentication credentials or exploiting other security weaknesses. Attackers can leverage this flaw to execute arbitrary SNMP queries against vulnerable systems, potentially gaining access to sensitive network information, configuration details, and operational data that should be restricted to authorized personnel only. The vulnerability affects both the UDP and TCP transport protocols used by SNMP, making it particularly dangerous as it can be exploited across different network communication methods. This issue directly relates to CWE-284, which describes improper access control vulnerabilities, and can be categorized under the ATT&CK technique T1078.101 for valid accounts and T1046 for network service scanning.
Security professionals should implement immediate mitigations including updating to net-snmp versions that contain patches addressing this specific vulnerability, typically those beyond 5.4.2.1. Organizations should also consider implementing additional network-level controls such as firewall rules that restrict access to SNMP ports (161/162) to known trusted IP addresses, and enable SNMPv3 authentication mechanisms where possible. The vulnerability demonstrates the importance of proper input validation and address parsing in network security software, particularly when dealing with access control mechanisms that rely on IP address information. System administrators should conduct thorough audits of their SNMP configurations and verify that TCP wrapper rules are properly implemented and tested to prevent similar issues in other network services that may be susceptible to the same class of vulnerability.