CVE-2006-2559 in WRT54G
Summary
by MITRE
Linksys WRT54G Wireless-G Broadband Router allows remote attackers to bypass access restrictions and conduct unauthorized operations via a UPnP request with a modified InternalClient parameter, which is not validated, as demonstrated by using AddPortMapping to forward arbitrary traffic.
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Analysis
by VulDB Data Team • 07/27/2018
The CVE-2006-2559 vulnerability affects the Linksys WRT54G Wireless-G Broadband Router, a widely deployed network device that implements Universal Plug and Play (UPnP) functionality for automatic port mapping and device discovery. This vulnerability represents a critical access control flaw that undermines the router's security model by allowing remote attackers to bypass authentication mechanisms through manipulation of UPnP requests. The vulnerability specifically targets the UPnP service implementation within the router's firmware, where the InternalClient parameter is not properly validated during port mapping operations.
The technical exploitation of this vulnerability occurs through a carefully crafted UPnP request that modifies the InternalClient parameter to point to arbitrary internal network addresses. When the router processes this malformed request, it fails to validate the parameter's legitimacy, allowing attackers to specify any internal IP address for port forwarding operations. This validation failure enables unauthorized users to perform AddPortMapping operations that would normally require legitimate authentication or authorization. The vulnerability stems from improper input validation and lacks proper access control checks within the UPnP implementation, making it susceptible to manipulation by remote attackers without requiring local access or credentials.
The operational impact of this vulnerability is significant as it allows remote attackers to establish unauthorized port forwarding rules that can expose internal network services to external threats. An attacker can use this vulnerability to redirect traffic from external ports to internal network devices, potentially gaining access to sensitive systems such as web servers, databases, or other networked equipment. This capability can lead to complete network compromise, data exfiltration, or the establishment of persistent backdoors. The vulnerability is particularly dangerous because it can be exploited from outside the network perimeter, requiring no prior authentication or physical access to the router, and can be leveraged to create persistent access points for further attacks.
The root cause of this vulnerability aligns with CWE-284, which describes improper access control in software implementations, and demonstrates weaknesses in the principle of least privilege enforcement. This vulnerability also maps to several ATT&CK techniques including T1071.004 for application layer protocols and T1021.001 for remote services. The lack of parameter validation in the UPnP service implementation creates a pathway for privilege escalation and lateral movement within networks. Network defenders should be aware that this vulnerability can be exploited as part of broader attack chains, potentially enabling more sophisticated threats such as command and control communications or internal network reconnaissance. The vulnerability highlights the importance of validating all external inputs, particularly in network services that handle device configuration and access control.
Mitigation strategies for this vulnerability include implementing network segmentation to isolate critical systems from exposed services, disabling UPnP functionality on routers when not required, and applying firmware updates from Linksys that address the validation issues. Network administrators should also implement firewall rules that restrict external access to UPnP ports and monitor for unusual port mapping activities. Regular network scanning and vulnerability assessments should include checks for exposed UPnP services, and organizations should consider implementing intrusion detection systems to monitor for suspicious UPnP activity. The most effective long-term solution involves updating to router firmware versions that properly validate UPnP parameters and enforce access controls, as well as adopting network security practices that minimize the attack surface of network devices.