CVE-2000-0115 in IIS
Summary
by MITRE
IIS allows local users to cause a denial of service via invalid regular expressions in a Visual Basic script in an ASP page.
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Analysis
by VulDB Data Team • 04/20/2026
The vulnerability described in CVE-2000-0115 represents a critical security flaw in Microsoft Internet Information Services version 5.0 that enables local users to execute denial of service attacks through malformed regular expressions within Visual Basic script components embedded in Active Server Pages. This vulnerability specifically targets the processing of regular expressions in ASP pages, where the IIS server fails to properly validate input parameters before executing regex operations. The flaw exists in the server-side script execution engine that handles Visual Basic Scripting Edition components, creating an opportunity for malicious input to disrupt normal service operations.
The technical implementation of this vulnerability stems from inadequate input validation within the IIS regular expression processing subsystem. When an ASP page contains Visual Basic script code with invalid or malformed regular expressions, the server's regex engine encounters unexpected input patterns that cause it to enter an unstable state or consume excessive system resources. This occurs because the regular expression parser does not properly handle malformed patterns or edge cases, leading to resource exhaustion or application crashes. The vulnerability specifically affects the VBScript engine's interaction with regular expression objects, where invalid regex syntax or patterns can trigger unhandled exceptions or infinite loops within the processing logic.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise system availability and stability. Local users who can access the server environment can exploit this weakness to consume significant CPU cycles and memory resources, effectively rendering the web server unresponsive to legitimate requests. The denial of service can manifest as complete service paralysis where the IIS server becomes unavailable or as partial disruption where only specific functionality is affected. This vulnerability particularly impacts web applications that rely heavily on regular expression matching for data validation or pattern recognition tasks, making it a significant concern for systems handling sensitive data processing or user input validation.
Mitigation strategies for CVE-2000-0115 should focus on both immediate patching and operational hardening measures. Microsoft released security updates that addressed the regex validation issues within the IIS server, and organizations should prioritize applying these patches to eliminate the vulnerability at its source. Additionally, implementing proper input validation and sanitization practices can help prevent malicious regex patterns from reaching the vulnerable processing components. Network segmentation and access controls should be enforced to limit local user access to the server environment, while monitoring systems should be deployed to detect unusual resource consumption patterns that may indicate exploitation attempts. This vulnerability aligns with CWE-129, which addresses improper validation of input boundaries, and represents a classic example of how inadequate input sanitization can lead to denial of service conditions. The attack pattern corresponds to techniques described in the ATT&CK framework under privilege escalation and denial of service tactics, where adversaries leverage application-level vulnerabilities to disrupt service availability. Organizations should also consider implementing web application firewalls and runtime application self-protection mechanisms to provide additional layers of defense against similar regex-based exploitation patterns.