CVE-2007-4991 in ISA Server
Summary
by MITRE
The SOCKS4 Proxy in Microsoft Internet Security and Acceleration (ISA) Server 2004 SP1 and SP2 allows remote attackers to obtain potentially sensitive information (the destination IP address of another user s session) via an empty packet.
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Analysis
by VulDB Data Team • 10/29/2017
The vulnerability described in CVE-2007-4991 represents a significant information disclosure flaw within Microsoft Internet Security and Acceleration (ISA) Server 2004, specifically affecting versions with Service Pack 1 and Service Pack 2. This issue resides in the SOCKS4 proxy implementation, which serves as a critical component for managing network traffic and access control within enterprise environments. The vulnerability manifests when the proxy server processes empty packets, creating an unintended information leakage channel that could expose sensitive session data to unauthorized parties.
The technical flaw stems from inadequate input validation within the SOCKS4 proxy protocol handler, where the system fails to properly sanitize or validate incoming packet data. When an empty packet is received, the proxy server inadvertently reveals the destination IP address associated with another user's session, effectively bypassing the normal access controls and privacy mechanisms that should protect session information. This behavior violates fundamental security principles of isolation and information flow control, as it allows one user to potentially access another user's network destination information through a simple malformed packet attack vector.
The operational impact of this vulnerability extends beyond mere information disclosure, as it creates opportunities for more sophisticated attacks within network environments. An attacker exploiting this flaw could map network topology, identify internal host addresses, and potentially establish subsequent attack vectors against other systems within the network infrastructure. The vulnerability particularly affects enterprise networks that rely on ISA Server for proxy services, as it undermines the trust model that should exist between users and network resources. This information leakage could enable attackers to conduct reconnaissance activities, identify high-value targets, and plan more targeted attacks against the organization's infrastructure.
From a cybersecurity framework perspective, this vulnerability aligns with CWE-200 (Information Exposure) and represents a classic example of how protocol implementation flaws can lead to unauthorized information disclosure. The issue also connects to ATT&CK technique T1046 (Network Service Scanning) and T1083 (File and Directory Discovery) as attackers could leverage this information to map network resources and identify potential targets. Organizations using ISA Server 2004 should implement immediate mitigations including applying the relevant security patches from Microsoft, implementing network segmentation to limit access to the affected proxy services, and monitoring for anomalous packet patterns that might indicate exploitation attempts. The vulnerability demonstrates the critical importance of proper input validation and the potential consequences of protocol implementation gaps in enterprise security infrastructure, particularly when dealing with proxy and firewall services that handle sensitive network traffic.