CVE-2005-1215 in ISA Server
Summary
by MITRE
Microsoft ISA Server 2000 allows remote attackers to poison the ISA cache or bypass content restriction policies via a malformed HTTP request packet containing multiple Content-Length headers.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 06/02/2019
Microsoft ISA Server 2000 contains a critical vulnerability that stems from improper handling of HTTP request parsing, specifically related to the Content-Length header field. This flaw exists within the server's HTTP protocol implementation where the system fails to properly validate or process multiple Content-Length headers within a single request. The vulnerability is classified as a buffer overflow and input validation issue that falls under CWE-129, which addresses improper validation of length fields. When a malformed HTTP request containing duplicate Content-Length headers is processed by the ISA Server, the system's parsing mechanism becomes confused about the actual content length of the request body, creating a condition where cache poisoning or policy bypass can occur.
The technical exploitation of this vulnerability occurs when an attacker crafts an HTTP request with multiple Content-Length headers that contain different values. The ISA Server processes these headers in a manner that allows the attacker to manipulate the cache behavior or override existing content restriction policies. This occurs because the server's internal cache mechanism relies on the Content-Length header to determine how much data to read and store, and when multiple headers are present, the system may use the first, last, or an intermediate value, leading to inconsistent behavior. The vulnerability operates at the application layer of the OSI model and represents a classic case of improper input validation that can lead to both information disclosure and access control bypass scenarios.
The operational impact of this vulnerability is significant for organizations relying on ISA Server 2000 for network security and content filtering. Attackers can exploit this weakness to bypass content restriction policies that are designed to prevent access to certain websites or types of content, potentially allowing malicious traffic to pass through the firewall undetected. Additionally, the cache poisoning aspect can lead to denial of service conditions where legitimate requests are corrupted or the cache becomes inconsistent, affecting the server's ability to properly filter traffic. This vulnerability directly impacts the integrity and availability of the security infrastructure, as it undermines the fundamental assumptions about how HTTP requests are processed and validated within the ISA Server environment. The attack vector is entirely remote, requiring no authentication or local access, making it particularly dangerous for organizations that do not properly segment their network infrastructure.
Organizations should implement immediate mitigations including applying the relevant Microsoft security patches that address this specific vulnerability, as well as configuring network-level protections such as intrusion detection systems that can identify and block malformed HTTP requests containing duplicate Content-Length headers. Network segmentation and additional firewall rules should be implemented to limit exposure, while monitoring should be enhanced to detect unusual patterns in HTTP traffic that might indicate exploitation attempts. The vulnerability also highlights the importance of proper HTTP protocol compliance and input validation in security appliances, aligning with ATT&CK technique T1071.004 which covers application layer protocol manipulation. Regular security assessments and vulnerability scanning should be conducted to identify similar issues in other network security devices, as this vulnerability represents a common pattern of improper header handling that can affect various web servers and proxy implementations.