CVE-2002-1908 in IIS
Summary
by MITRE
Microsoft IIS 5.0 and 5.1 allows remote attackers to cause a denial of service (CPU consumption) via an HTTP request with a Host header that contains a large number of "/" (forward slash) characters.
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Analysis
by VulDB Data Team • 09/01/2025
Microsoft Internet Information Services versions 5.0 and 5.1 contain a critical vulnerability that enables remote attackers to execute denial of service attacks through carefully crafted HTTP requests. This vulnerability specifically targets the processing of Host headers within HTTP requests, where an attacker can construct malicious requests containing an excessive number of forward slash characters. The flaw resides in how IIS handles these malformed Host headers during request parsing and validation processes, creating a condition where the server consumes excessive CPU resources in attempting to process the malformed input. The technical implementation of this vulnerability maps to CWE-400, which describes unrestricted resource consumption, and represents a classic example of a resource exhaustion attack that can effectively瘫痪 entire web servers. When an attacker sends multiple HTTP requests with Host headers containing thousands or even millions of forward slashes, the IIS server enters into a computationally intensive loop attempting to parse and validate these malformed headers, leading to sustained high CPU utilization that can render the web server unavailable to legitimate users. This vulnerability directly impacts the availability aspect of the CIA triad and can be classified under ATT&CK technique T1499.004, which covers network denial of service attacks. The operational impact extends beyond simple service disruption as it can affect multiple concurrent connections and potentially cause cascading failures in web server infrastructure. Organizations running these vulnerable versions of IIS face significant risk of being unable to serve legitimate web traffic, with the attack requiring minimal resources to execute and potentially causing extended outages. The vulnerability demonstrates a fundamental flaw in input validation mechanisms within the web server software, where insufficient bounds checking allows malformed data to trigger excessive processing cycles. Attackers can easily automate this attack by crafting simple scripts that generate requests with increasing numbers of forward slashes, making it particularly dangerous for systems with limited computational resources. The attack vector is particularly insidious because it does not require authentication or specialized privileges, making it accessible to any remote attacker with basic network connectivity. The affected systems include all versions of Microsoft IIS 5.0 and 5.1, which were widely deployed in enterprise environments during the early 2000s, creating a substantial attack surface for this vulnerability. Mitigation strategies should include immediate patching of the affected IIS versions, implementation of rate limiting mechanisms, and configuration changes that restrict the length of Host headers processed by the server. Network-level protections such as intrusion detection systems can help detect and block these malformed requests, while application-level firewalls can provide additional layers of defense. Organizations should also consider implementing monitoring solutions that can detect unusual CPU consumption patterns that may indicate exploitation attempts. The vulnerability serves as a critical reminder of the importance of robust input validation and resource management in web server implementations, particularly in environments where public-facing services are exposed to untrusted network traffic. This flaw highlights the need for comprehensive security testing and the implementation of defense-in-depth strategies that protect against various attack vectors including resource exhaustion attacks that can severely impact service availability.