CVE-2003-0110 in Proxy Server
Summary
by MITRE
The Winsock Proxy service in Microsoft Proxy Server 2.0 and the Microsoft Firewall service in Internet Security and Acceleration (ISA) Server 2000 allow remote attackers to cause a denial of service (CPU consumption or packet storm) via a spoofed, malformed packet to UDP port 1745.
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Analysis
by VulDB Data Team • 08/25/2025
The vulnerability identified as CVE-2003-0110 represents a critical denial of service flaw affecting Microsoft Proxy Server 2.0 and Internet Security and Acceleration (ISA) Server 2000. This weakness resides within the Winsock Proxy service and Firewall service components that handle network traffic processing. The vulnerability specifically targets UDP port 1745, which is used for the Microsoft Proxy Server's internal communication protocols. Attackers can exploit this flaw by crafting and transmitting spoofed or malformed packets to this designated port, triggering abnormal system behavior that can lead to complete service unavailability.
The technical mechanism behind this vulnerability involves the improper handling of malformed UDP packets received on port 1745. When the affected Microsoft services process these malicious packets, they fail to properly validate or sanitize the incoming data structure. This processing error causes the system to enter an infinite loop or consume excessive CPU resources while attempting to parse the malformed data. The vulnerability demonstrates characteristics consistent with CWE-129, which addresses improper validation of input boundaries, and CWE-400, which covers unspecified resource management issues. The flawed packet processing logic creates a condition where legitimate system resources become consumed indefinitely, leading to system performance degradation or complete service exhaustion.
The operational impact of this vulnerability extends beyond simple service disruption, as it can potentially create network-wide packet storms that affect connected systems. When exploited, the vulnerability allows remote attackers to consume system resources without requiring authentication or specific privileges, making it particularly dangerous in enterprise environments where these services are critical for network security and access control. The attack vector is particularly concerning because it leverages the fundamental network protocol processing capabilities of the affected systems, potentially causing cascading failures throughout the network infrastructure. This vulnerability aligns with ATT&CK technique T1498, which covers denial of service attacks targeting network services, and represents a classic example of how protocol implementation flaws can be weaponized for system compromise.
Organizations affected by this vulnerability should immediately implement network segmentation to isolate the affected servers and prevent unauthorized access to UDP port 1745. The most effective mitigations include applying the official Microsoft security patches released in response to this vulnerability, configuring network access controls to restrict UDP port 1745 access, and implementing network monitoring to detect unusual packet patterns on this port. System administrators should also consider disabling unnecessary proxy services when they are not actively required, as this reduces the attack surface. Additionally, implementing intrusion detection systems with signature-based detection for this specific vulnerability pattern can help identify exploitation attempts. The vulnerability underscores the importance of proper input validation and resource management in network service implementations, as highlighted by industry standards that emphasize secure coding practices and defensive programming techniques.