CVE-2005-1216 in ISA Server
Summary
by MITRE
Microsoft ISA Server 2000 allows remote attackers to connect to services utilizing the NetBIOS protocol via a NetBIOS connection with an ISA Server that uses the NetBIOS (all) predefined packet filter.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 07/04/2025
Microsoft ISA Server 2000 contains a significant security vulnerability that stems from its improper handling of NetBIOS protocol connections within its packet filtering mechanisms. This flaw exists specifically when the server utilizes the "NetBIOS (all)" predefined packet filter configuration, which creates an unintended pathway for remote attackers to establish unauthorized connections to services that typically would be restricted. The vulnerability represents a classic case of insufficient network boundary control where the firewall fails to properly enforce access restrictions for legacy NetBIOS protocols that were designed for internal network environments rather than external internet exposure.
The technical implementation of this vulnerability exploits the fundamental mismatch between ISA Server's packet filtering logic and the inherent characteristics of NetBIOS communication patterns. NetBIOS operates on a broadcast-based model using specific port numbers and packet structures that are not adequately filtered by the default "NetBIOS (all)" rule set. This allows attackers to bypass the intended security boundaries by establishing NetBIOS connections that the firewall should have blocked, effectively creating a backdoor access mechanism to internal services. The vulnerability is particularly concerning because NetBIOS was originally designed for local area networks and lacks the authentication and encryption mechanisms necessary for secure internet communication.
From an operational perspective, this vulnerability enables remote attackers to gain unauthorized access to services running on the ISA Server that are configured to use NetBIOS protocols. The impact extends beyond simple network access as attackers can potentially leverage this entry point to escalate privileges, conduct reconnaissance, or launch further attacks against internal network resources. The attack vector is particularly dangerous because it requires minimal privileges to exploit and can be automated, making it attractive to both casual attackers and more sophisticated threat actors. The vulnerability affects organizations that have legacy systems or applications that depend on NetBIOS functionality, creating a false sense of security when the ISA Server's default configurations are in place.
Organizations should immediately implement mitigations that involve modifying the packet filtering rules to explicitly deny NetBIOS traffic at the ISA Server level, particularly when the server is exposed to untrusted networks. The recommended approach includes configuring more restrictive firewall rules that only allow necessary NetBIOS traffic from trusted internal sources while blocking all external NetBIOS connections. Security practitioners should also consider implementing network segmentation to isolate ISA Server instances from external networks and deploy additional monitoring solutions to detect unusual NetBIOS traffic patterns. This vulnerability aligns with CWE-668, which describes "Exposure of Resource to Wrong Sphere" and maps to ATT&CK technique T1071.004 for application layer protocol usage. The remediation process should include comprehensive network audits to identify all systems that may be affected by this configuration and the implementation of network access control policies that align with the principle of least privilege.
The broader implications of this vulnerability highlight the critical importance of proper firewall configuration and the dangers of relying on default security settings in enterprise environments. Organizations must recognize that legacy protocols like NetBIOS, while functional in controlled internal environments, pose significant security risks when exposed to external networks without proper filtering mechanisms. This vulnerability serves as a reminder of the need for regular security assessments and the importance of maintaining up-to-date security configurations that account for both current and emerging threats in the cybersecurity landscape.