CVE-2000-0331 in Windows
Summary
by MITRE
Buffer overflow in Microsoft command processor (CMD.EXE) for Windows NT and Windows 2000 allows a local user to cause a denial of service via a long environment variable, aka the "Malformed Environment Variable" vulnerability.
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Analysis
by VulDB Data Team • 04/21/2026
The vulnerability identified as CVE-2000-0331 represents a critical buffer overflow flaw within the Microsoft command processor CMD.EXE that affects Windows NT and Windows 2000 operating systems. This issue stems from inadequate input validation mechanisms within the command execution environment, specifically when processing environment variables that exceed predetermined memory boundaries. The vulnerability operates at the system level where the command processor fails to properly sanitize or limit the length of environment variables before processing them, creating an exploitable condition that can be leveraged by local attackers.
The technical implementation of this buffer overflow occurs when a maliciously crafted environment variable exceeds the allocated buffer space within CMD.EXE's memory management structure. This condition typically manifests when environment variables contain excessively long strings that surpass the predefined buffer limits, causing memory corruption that results in program termination or system instability. The flaw falls under the CWE-121 category of stack-based buffer overflow, though it specifically impacts the environment variable handling mechanism rather than traditional stack operations. The vulnerability demonstrates characteristics consistent with CWE-787, where an application writes to a memory location outside the boundaries of a provided buffer, leading to unpredictable behavior.
From an operational perspective, this vulnerability presents a significant risk for local users who can exploit it to cause denial of service conditions within the targeted system. The attack requires local system access but does not necessitate elevated privileges, making it particularly concerning for environments where multiple users share system resources. When successfully exploited, the buffer overflow causes CMD.EXE to crash or terminate unexpectedly, resulting in service disruption that can impact legitimate system operations and user productivity. The vulnerability also aligns with ATT&CK technique T1489, which involves creating or manipulating system resources to deny service to legitimate users.
The mitigation strategies for CVE-2000-0331 primarily involve implementing proper input validation and length checking mechanisms within the command processor's environment variable handling code. Microsoft addressed this vulnerability through security updates that included buffer size limitations and enhanced input sanitization for environment variables. System administrators should ensure that all Windows NT and Windows 2000 systems are patched with the appropriate security updates released by Microsoft. Additionally, implementing proper environment variable management practices, including monitoring for unusually long environment variables, can help detect potential exploitation attempts. The vulnerability also underscores the importance of following secure coding practices such as those outlined in the CERT/CC Secure Coding Standards, particularly guidelines related to buffer management and input validation to prevent similar issues in future software development cycles.