CVE-1999-0994 in Windows
Summary
by MITRE
Windows NT with SYSKEY reuses the keystream that is used for encrypting SAM password hashes, allowing an attacker to crack passwords.
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Analysis
by VulDB Data Team • 04/19/2026
This vulnerability exists in Windows nt systems that utilize the SYSKEY feature for protecting the security account manager database. The flaw stems from a cryptographic implementation error where the same keystream is repeatedly used for encrypting multiple password hashes within the SAM database. This represents a critical weakness in the encryption protocol that directly violates fundamental cryptographic principles outlined in cwe-327, which addresses the use of weak or broken cryptographic algorithms. The vulnerability specifically impacts systems where SYSKEY is enabled, typically Windows nt 4.0 and earlier versions, though it may affect other legacy systems that implement similar encryption mechanisms. The reuse of keystreams creates a mathematical vulnerability that allows attackers to perform differential cryptanalysis against the encrypted password hashes.
The operational impact of this vulnerability is severe as it fundamentally undermines the security of password authentication on affected systems. An attacker who gains access to the SAM database file can exploit this weakness to reverse engineer password hashes without requiring brute force attacks that would normally take considerable computational time. This vulnerability enables password cracking attacks that align with techniques described in the attack pattern taxonomy under attack-0004, specifically targeting credential access through cryptanalysis. The flaw allows for the extraction of cleartext passwords from the encrypted hashes, effectively bypassing the intended security measures. Systems that rely on Windows nt authentication mechanisms become particularly vulnerable as the entire password database becomes compromised through this single cryptographic weakness.
Mitigation strategies for this vulnerability require immediate system updates and configuration changes to address the underlying cryptographic implementation. Organizations should disable SYSKEY functionality on affected systems when possible, as this removes the vulnerable encryption mechanism entirely. The most effective remediation involves upgrading to supported Windows versions that implement proper cryptographic practices and do not reuse keystreams for encryption operations. System administrators must also implement additional security controls such as account lockout policies and strong password requirements to minimize the impact of any successful attacks. Security monitoring should be enhanced to detect unauthorized access attempts to the SAM database and other system files that may indicate exploitation attempts. This vulnerability demonstrates the critical importance of proper cryptographic implementation as outlined in industry standards and emphasizes the need for regular security assessments to identify similar weaknesses in authentication systems. The incident highlights the necessity of following established cryptographic best practices and avoiding known weak implementations that could compromise entire authentication infrastructures.