CVE-1999-0995 in Windows
Summary
by MITRE
Windows NT Local Security Authority (LSA) allows remote attackers to cause a denial of service via malformed arguments to the LsaLookupSids function which looks up the SID, aka "Malformed Security Identifier Request."
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Analysis
by VulDB Data Team • 04/19/2026
The vulnerability identified as CVE-1999-0995 resides within the Windows NT Local Security Authority component, specifically targeting the LsaLookupSids function that handles security identifier lookups. This flaw represents a classic buffer overflow condition that occurs when the function processes malformed input arguments, creating an opportunity for remote attackers to exploit the system's security infrastructure. The vulnerability exists at the core of Windows NT's authentication and authorization mechanisms, making it particularly dangerous as it directly impacts the system's ability to maintain secure access controls. The LSA service operates with elevated privileges and is responsible for managing security policies and user authentication, rendering any compromise of this component potentially catastrophic for system security.
The technical implementation of this vulnerability stems from inadequate input validation within the LsaLookupSids function, which fails to properly sanitize or limit the size of arguments passed to the security identifier lookup process. When attackers submit malformed security identifier requests containing oversized or malformed data structures, the function's internal buffer management fails to handle the unexpected input gracefully, leading to memory corruption that ultimately results in system instability. This type of vulnerability aligns with CWE-121, which categorizes buffer overflow conditions where insufficient bounds checking allows attackers to overwrite adjacent memory locations. The flaw demonstrates characteristics of a remote code execution vector that can be leveraged to cause system crashes or restarts, effectively creating a denial of service condition that disrupts legitimate user access to the system.
The operational impact of this vulnerability extends beyond simple system availability concerns, as it represents a fundamental weakness in Windows NT's security architecture that could enable more sophisticated attacks. Attackers exploiting this flaw can cause unpredictable system behavior including application crashes, system reboots, or complete service unavailability, which directly affects the organization's operational continuity and user productivity. The vulnerability's remote exploitability means that attackers need not have physical access to the system or even be on the same network segment, making it particularly dangerous in enterprise environments where Windows NT systems may be exposed to external networks. From an attack perspective, this vulnerability maps to ATT&CK technique T1499 which involves network denial of service attacks, and T1070 which covers indicator removal on systems, as the system instability may obscure legitimate security events.
Mitigation strategies for this vulnerability require immediate patching of affected Windows NT systems with the appropriate security updates from Microsoft, as this flaw was addressed in subsequent service packs and security releases. Organizations should implement network segmentation to limit access to systems running Windows NT, particularly those with elevated privileges, and establish monitoring procedures to detect unusual authentication patterns or system instability that may indicate exploitation attempts. System administrators should also consider implementing additional access controls and limiting the exposure of LSA services to unnecessary network access. The vulnerability highlights the importance of proper input validation and bounds checking in security-critical system components, emphasizing that even fundamental authentication services require rigorous security testing and validation. Organizations with legacy Windows NT systems should develop migration plans to modern operating systems that have more robust security implementations and better support for contemporary threat landscapes.