CVE-2007-2999 in Windows
Summary
by MITRE
Microsoft Windows Server 2003, when time restrictions are in effect for user accounts, generates different error messages for failed login attempts with a valid user name than for those with an invalid user name, which allows context-dependent attackers to determine valid Active Directory account names.
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Analysis
by VulDB Data Team • 09/17/2018
This vulnerability exists in Microsoft Windows Server 2003 systems where time restrictions are enforced for user accounts. The flaw stems from the inconsistent error messaging behavior during authentication attempts, creating a side-channel information leakage mechanism that can be exploited by attackers to enumerate valid Active Directory accounts. The vulnerability is categorized under CWE-200 Information Exposure and represents a classic example of how error handling can inadvertently reveal sensitive information about system state. When authentication fails, the system provides different error messages depending on whether the username exists in the directory or not, creating a distinguishable pattern that attackers can exploit.
The technical implementation of this vulnerability occurs at the authentication layer where Windows Server 2003's security subsystem differentiates between valid and invalid usernames during the login process. When a user attempts to authenticate with an account that has time restrictions, the system returns distinct error codes or messages that indicate whether the account exists in Active Directory. This differential response allows attackers to perform account enumeration by systematically testing usernames and observing the different error responses. The vulnerability is particularly dangerous because it operates within the legitimate authentication flow, making it difficult to detect through standard monitoring mechanisms. Attackers can leverage this behavior to build comprehensive lists of valid user accounts, which can then be used for subsequent attacks such as password spraying or brute force attempts.
The operational impact of this vulnerability extends beyond simple account enumeration, as it significantly weakens the overall security posture of Windows Server 2003 environments. By enabling attackers to discover valid Active Directory accounts, the vulnerability creates a foundation for more sophisticated attacks that can bypass other security controls. The information leakage occurs during the authentication phase and can be exploited through automated tools that rapidly test various usernames against the system. This vulnerability is particularly concerning in environments where time restrictions are implemented for security purposes, as the very mechanism designed to enhance security inadvertently creates a weakness. The impact is further amplified when combined with other reconnaissance techniques, as the valid account information can be used to target specific accounts with more focused attack vectors.
Mitigation strategies for this vulnerability should focus on implementing consistent error handling across authentication systems and disabling time restriction features that create this information leakage. Organizations should configure their Windows Server 2003 systems to provide uniform error messages regardless of whether a username exists in Active Directory. This approach aligns with the principle of least information disclosure and prevents attackers from distinguishing between valid and invalid account attempts. The recommended solution involves modifying the authentication configuration to ensure that all failed login attempts return identical error responses, thereby eliminating the side-channel information leakage. Security administrators should also consider implementing account lockout policies and other authentication controls that do not rely on time-based restrictions that create this vulnerability. Additionally, network-level protections such as intrusion detection systems can be configured to monitor for unusual authentication patterns that might indicate account enumeration attempts. This vulnerability demonstrates the importance of considering information leakage in security design and aligns with ATT&CK technique T1078 Account Manipulation which involves using valid accounts to bypass security controls.