CVE-2001-1243 in IIS
Summary
by MITRE
Scripting.FileSystemObject in asp.dll for Microsoft IIS 4.0 and 5.0 allows local or remote attackers to cause a denial of service (crash) via (1) creating an ASP program that uses Scripting.FileSystemObject to open a file with an MS-DOS device name, or (2) remotely injecting the device name into ASP programs that internally use Scripting.FileSystemObject.
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Analysis
by VulDB Data Team • 01/27/2025
The vulnerability described in CVE-2001-1243 represents a significant denial of service weakness within Microsoft Internet Information Services versions 4.0 and 5.0. This flaw specifically targets the Scripting.FileSystemObject component embedded in asp.dll, which serves as a critical interface for ASP applications to interact with the file system. The vulnerability operates through the exploitation of MS-DOS device names, which are special reserved identifiers that have been part of the Windows operating system architecture since its earliest versions. These device names include constructs such as CON, PRN, AUX, NUL, and COM1 through COM9, along with LPT1 through LPT9, which were originally designed for hardware device access but have since been repurposed for system-level operations within the file system namespace.
The technical mechanism behind this vulnerability involves the improper handling of device names within the Scripting.FileSystemObject implementation. When an ASP program attempts to access a file using a device name, the underlying system components fail to properly validate or sanitize these inputs, leading to unpredictable behavior that can result in application crashes. The vulnerability manifests in two distinct attack vectors that exploit the same underlying flaw. The first vector involves local attackers who create malicious ASP programs that directly reference device names through the FileSystemObject, while the second vector allows remote attackers to inject device names into ASP applications that internally utilize the FileSystemObject for file operations. Both attack scenarios leverage the fundamental weakness in input validation and sanitization within the ASP scripting engine, causing the IIS server process to terminate unexpectedly and resulting in a denial of service condition that affects legitimate user access to web applications.
The operational impact of this vulnerability extends beyond simple service disruption, as it represents a critical weakness in the core web server functionality that could be exploited by attackers to maintain persistent availability issues for web applications. From a cybersecurity perspective, this vulnerability aligns with CWE-20, which describes improper input validation, and demonstrates how legacy system components can introduce security weaknesses that persist across multiple generations of software. The attack pattern corresponds to techniques found in the MITRE ATT&CK framework under the T1499 category, specifically targeting network denial of service through application layer attacks. Organizations running IIS 4.0 and 5.0 were particularly vulnerable because these versions lacked proper input sanitization mechanisms for device name handling, creating a persistent attack surface that could be exploited without requiring elevated privileges or complex exploitation techniques. The vulnerability essentially allows attackers to crash web server processes through simple file access operations, making it a particularly dangerous weakness in server-side application environments where availability is paramount.
Mitigation strategies for this vulnerability should focus on immediate patching of affected IIS versions, as Microsoft released security updates specifically addressing this issue in their regular security bulletins. Organizations should implement proper input validation within ASP applications to prevent device name injection, particularly in user-facing input fields that might be processed by FileSystemObject operations. Network-level protections including firewall rules and web application firewalls can help detect and block suspicious file access patterns, while monitoring systems should be configured to alert on unusual process termination events related to IIS services. Additionally, administrators should consider implementing application sandboxing techniques to limit the impact of potential exploitation and ensure that even if an attacker successfully exploits this vulnerability, the broader system remains protected. The vulnerability underscores the importance of maintaining up-to-date security patches and implementing proper input validation practices, as it demonstrates how seemingly benign file system operations can be leveraged for significant system disruption. Organizations should also consider migrating away from legacy IIS versions that are no longer supported, as these older systems often contain multiple unpatched vulnerabilities that create persistent security risks.