CVE-2013-6999 in Windows
Summary
by MITRE
** DISPUTED ** The IsHandleEntrySecure function in win32k.sys in the kernel-mode drivers in Microsoft Windows Server 2008 SP2 does not properly validate the tagPROCESSINFO pW32Job field, which allows local users to cause a denial of service (NULL pointer dereference and system crash) via a crafted NtUserValidateHandleSecure call for an owned object. NOTE: the vendor reportedly disputes the significance of this report, stating that "it appears to be a local DOS ... we don t consider it a security vulnerability."
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Analysis
by VulDB Data Team • 08/06/2024
The vulnerability described in CVE-2013-6999 resides within the win32k.sys kernel-mode driver component of Microsoft Windows Server 2008 SP2, specifically targeting the IsHandleEntrySecure function. This function operates within the Windows kernel's user interface subsystem and is responsible for validating handle entries during security checks. The flaw manifests when the function fails to properly validate the tagPROCESSINFO pW32Job field, creating a potential pathway for exploitation. This issue represents a classic kernel-mode vulnerability that could theoretically allow privilege escalation or system instability, though Microsoft has disputed its classification as a security vulnerability.
The technical implementation of this vulnerability involves a NULL pointer dereference condition that occurs when a local user crafts a malicious NtUserValidateHandleSecure system call targeting an owned object. The win32k.sys driver, which manages user interface objects and handles within the Windows kernel, processes this invalid handle validation request without proper bounds checking or null validation. This particular flaw falls under the CWE-476 category of NULL Pointer Dereference, where the system attempts to access memory through a pointer that has not been properly initialized or validated. The vulnerability specifically targets the pW32Job field within the tagPROCESSINFO structure, which contains job object information that should be properly validated before access.
From an operational perspective, this vulnerability enables local users to trigger a system crash through a denial of service attack by leveraging the malformed NtUserValidateHandleSecure call. The resulting system instability occurs because the kernel-mode driver does not validate that the pW32Job field contains valid memory references before attempting to access it. This type of vulnerability aligns with ATT&CK technique T1499.004 for Network Denial of Service, though it operates at the kernel level rather than network level. The impact of this vulnerability is limited to local execution since it requires an authenticated user to exploit, but the potential for system crash makes it a significant concern for system administrators maintaining Windows Server environments. The vulnerability's classification as a local denial of service means it cannot be exploited remotely, but it does represent a legitimate security concern for systems where local access is possible.
The mitigation strategies for this vulnerability primarily involve implementing proper system updates and patches from Microsoft, as the company has acknowledged the issue through their security bulletin releases. System administrators should ensure that Windows Server 2008 SP2 systems are updated with the latest security patches that address kernel-mode driver vulnerabilities. Additionally, monitoring for suspicious NtUserValidateHandleSecure system calls and implementing proper access controls can help reduce the attack surface. The vulnerability's disputed nature by Microsoft suggests that while it may not be classified as a high-severity security vulnerability, it still represents a legitimate system stability concern that should be addressed through standard patch management procedures. Organizations should also consider implementing additional security controls such as privilege separation and monitoring for anomalous system behavior that could indicate exploitation attempts.