CVE-1999-1316 in Windows
Summary
by MITRE
Passfilt.dll in Windows NT SP2 allows users to create a password that contains the user's name, which could make it easier for an attacker to guess.
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Analysis
by VulDB Data Team • 04/20/2026
The vulnerability described in CVE-1999-1316 resides in the passfilt.dll component of Windows NT Service Pack 2, representing a significant weakness in the operating system's password policy enforcement mechanisms. This flaw specifically affects the password filtering process that occurs during password changes and account creation operations. The vulnerability manifests when the system fails to properly validate that passwords do not contain the username as a substring, creating a predictable pattern that undermines the fundamental security principle of password complexity.
This technical weakness falls under the category of weak password validation, which is classified as CWE-521 in the Common Weakness Enumeration framework. The flaw enables attackers to exploit predictable password patterns by using the username as a component of the password, significantly reducing the entropy and guessability of user credentials. The vulnerability is particularly concerning because it operates at the system level within the authentication framework, affecting the core password validation process rather than being a peripheral security feature.
The operational impact of this vulnerability extends beyond simple password guessing, as it creates a foundation for more sophisticated attacks within the Windows NT environment. Attackers can leverage this weakness to conduct targeted password guessing campaigns, where they systematically test variations of usernames combined with common dictionary words or patterns. This vulnerability directly relates to the ATT&CK technique T1110.001, which covers credential guessing through password spraying and targeted attacks using known information about users. The reduced password entropy makes it significantly easier for both automated tools and manual attackers to compromise accounts through dictionary attacks or brute force methods.
The implications of this vulnerability are particularly severe in enterprise environments where Windows NT systems may still be operational, as it represents a fundamental flaw in the authentication infrastructure that predates modern security standards. Organizations running affected systems face increased risk of unauthorized access, privilege escalation, and potential lateral movement within their networks. The vulnerability demonstrates a critical gap in the password policy enforcement that existed in Windows NT SP2, where the system's built-in protections against predictable password patterns were insufficient. Security professionals should recognize this as a historical example of how inadequate input validation and password policy enforcement can create persistent security weaknesses that remain exploitable in legacy systems.
Mitigation strategies for this vulnerability primarily involve implementing stronger password policies that explicitly prohibit the use of usernames within passwords, though this requires system-level configuration changes that may not be available in older Windows NT versions. Organizations should consider upgrading to more recent operating systems where such vulnerabilities have been addressed through improved password validation mechanisms and enhanced security features. The vulnerability also highlights the importance of regular security assessments and the need for organizations to maintain up-to-date systems, as this flaw represents a basic security failure that modern authentication systems have largely resolved through improved validation algorithms and policy enforcement mechanisms.