CVE-2003-0011 in ISA Server
Summary
by MITRE
Unknown vulnerability in the DNS intrusion detection application filter for Microsoft Internet Security and Acceleration (ISA) Server 2000 allows remote attackers to cause a denial of service (blocked traffic to DNS servers) via a certain type of incoming DNS request that is not properly handled.
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Analysis
by VulDB Data Team • 08/26/2025
The vulnerability identified as CVE-2003-0011 represents a critical flaw in Microsoft Internet Security and Acceleration ISA Server 2000's DNS intrusion detection application filter. This weakness specifically targets the handling of certain DNS request types within the security infrastructure, creating a potential avenue for remote attackers to disrupt network operations. The vulnerability manifests when the system encounters particular incoming DNS requests that fall outside the normal processing parameters of the application filter, leading to unexpected behavior that ultimately results in service disruption. The flaw exists within the ISA Server 2000's security framework, which is designed to protect network infrastructure from various threats including DNS-based attacks, making this vulnerability particularly concerning for organizations relying on this protection mechanism.
The technical implementation of this vulnerability stems from inadequate input validation and error handling within the DNS application filter component of ISA Server 2000. When the system receives a specially crafted DNS request that does not conform to expected patterns or contains malformed data, the application filter fails to properly process the request and instead triggers a condition that causes the system to block legitimate DNS traffic. This behavior creates a denial of service scenario where authorized network traffic destined for DNS servers becomes blocked or disrupted, effectively preventing users from resolving domain names and accessing internet resources. The vulnerability operates at the application layer of the network stack, specifically targeting the DNS protocol handling capabilities of the security appliance. This type of flaw typically maps to CWE-20, which describes improper input validation, and CWE-400, which covers resource exhaustion conditions that can lead to denial of service attacks.
The operational impact of CVE-2003-0011 extends beyond simple service interruption, as it fundamentally undermines the security posture of networks relying on ISA Server 2000 for DNS protection. Organizations experiencing this vulnerability may face complete disruption of DNS resolution services, leading to cascading effects throughout their network infrastructure. The attack vector is particularly dangerous because it requires no authentication or privileged access, allowing any remote attacker to exploit the flaw. This vulnerability creates a persistent threat that can be leveraged for extended periods, as the affected systems remain vulnerable until patched or upgraded. Network administrators may observe increased error rates, failed DNS queries, and overall degraded network performance as the malicious requests cause the application filter to malfunction and block legitimate traffic. The vulnerability also exposes organizations to potential reconnaissance activities where attackers can use the denial of service condition to verify the presence of vulnerable systems within their network perimeter.
Mitigation strategies for CVE-2003-0011 primarily involve immediate application of Microsoft security patches and updates to ISA Server 2000 installations. Organizations should prioritize upgrading to the latest available service packs and security updates that address this specific vulnerability. Network administrators should also implement additional monitoring and alerting mechanisms to detect unusual DNS traffic patterns that might indicate exploitation attempts. The implementation of redundant DNS infrastructure and failover mechanisms can help maintain service availability during exploitation attempts. From an operational security perspective, organizations should consider implementing network segmentation to isolate critical DNS services from potentially vulnerable ISA server configurations. The vulnerability's characteristics align with ATT&CK technique T1499.004, which describes network denial of service attacks, and T1071.004, which covers application layer protocol usage for command and control communications. Organizations should also review their incident response procedures to ensure preparedness for handling denial of service conditions that may arise from this vulnerability. System administrators must conduct thorough vulnerability assessments to identify all instances of ISA Server 2000 within their network infrastructure and prioritize remediation efforts accordingly.