CVE-2023-29336
Microsoft Win32K Privilege Escalation Vulnerability
Description
CVE-2023-29336 is a high-severity elevation of privilege vulnerability in Microsoft's Win32k kernel-mode driver, caused by a use-after-free weakness (CWE-416). A locally authenticated attacker can exploit this flaw to escalate privileges from a low-privilege user context to SYSTEM level on affected Windows systems, including Windows 10 and Windows Server 2008, 2012, and 2016. CISA has confirmed active exploitation in the wild, and with an EPSS score of 79.5% (99th percentile), exploitation is highly likely. Public exploit code is available, making immediate patching essential for organizations running affected legacy Windows versions.
KEV Information
CVSS Score
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:HOpen in CalculatorAffected Products
| Vendor | Product | Version |
|---|---|---|
| microsoft | windows 10 1507 | < 10.0.10240.19926 |
| microsoft | windows 10 1607 | < 10.0.14393.5921 |
| microsoft | windows server 2008 | -; r2 |
| microsoft | windows server 2012 | -; r2 |
| microsoft | windows server 2016 | - |
References
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-29336(Patch, Vendor Advisory)
- https://www.exploit-db.com/exploits/52301(Exploit)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2023-29336(US Government Resource)
Weakness Type
CWE-416: Use After Free
CVE-2023-29336 is caused by a use-after-free vulnerability in the Win32k kernel component. Use-after-free occurs when a program continues to reference memory after it has been freed, allowing an attacker to manipulate that memory region to execute arbitrary code or escalate privileges. In the case of Win32k, the kernel-mode driver improperly handles objects in memory, enabling a local attacker to corrupt kernel memory structures and gain SYSTEM-level privileges.
Learn more: CWE-416 — Use After Free
Impact Analysis
CVE-2023-29336 carries a CVSS 3.1 base score of 7.8 (HIGH) with the vector CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Attack Vector (Local): the attacker must have local access to the target system, meaning remote exploitation is not directly possible without a prior foothold such as a phishing-delivered payload or another remote vulnerability. Attack Complexity (Low): the exploitation requires no special conditions or race conditions, making it reliable once local access is obtained. Privileges Required (Low): the attacker needs only a low-privilege user account, which is commonly available in enterprise environments. User Interaction (None): no victim action is required beyond the attacker's own execution. Confidentiality, Integrity, and Availability (all High): successful exploitation grants SYSTEM-level privileges, allowing the attacker to read any data, modify system configurations, install persistent backdoors, and disrupt services. This vulnerability is particularly dangerous as a post-exploitation privilege escalation step, commonly chained after initial access via phishing or remote code execution vulnerabilities.
Exploit Maturity
Public exploit code is available for CVE-2023-29336 via Exploit-DB, providing attackers with a ready-to-use proof of concept for the Win32k use-after-free elevation of privilege. CISA has confirmed active exploitation in the wild by adding this vulnerability to the Known Exploited Vulnerabilities catalog with a remediation deadline of May 30, 2023. The EPSS score of 79.5% (99th percentile) indicates a very high probability of continued exploitation activity. While the ransomware usage status is listed as unknown, the combination of public exploit availability, confirmed active exploitation, and the value of SYSTEM-level privilege escalation to attackers makes CVE-2023-29336 a high-priority remediation target.
Remediation
- Apply Microsoft security updates immediately: Install the patches released by Microsoft in the May 2023 Patch Tuesday update that address CVE-2023-29336 in the Win32k component. Refer to the Microsoft Security Response Center advisory for specific KB articles and version guidance.
- Prioritize legacy systems: CVE-2023-29336 affects Windows 10 version 1507, Windows 10 version 1607, Windows Server 2008, Windows Server 2012, and Windows Server 2016 — ensure these older systems receive immediate attention as they are the confirmed affected platforms.
- Apply mitigations per CISA KEV guidance: Per the KEV required action, apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable. The CISA remediation deadline was May 30, 2023.
- Implement defense-in-depth measures: Restrict local logon privileges to minimize the number of accounts that could be used to exploit this vulnerability, enforce least-privilege access policies, and deploy endpoint detection and response (EDR) tools to detect kernel exploitation attempts.
- Monitor for indicators of compromise: Review system event logs for signs of Win32k exploitation, suspicious privilege escalation events, and unexpected SYSTEM-level process creation from low-privilege user sessions.
Technical Details
CVE-2023-29336 is a use-after-free vulnerability (CWE-416) in the Win32k kernel-mode driver, a core Windows component responsible for managing window objects, graphical rendering, and user-mode callback handling. Use-after-free vulnerabilities occur when a program dereferences a pointer to memory that has already been freed, allowing an attacker to reclaim and control that memory region with crafted data. In the Win32k context, the driver improperly handles the lifetime of certain window or menu objects in kernel memory. Exploitation mechanism: a local attacker with low privileges creates specific window object structures that trigger the use-after-free condition during Win32k processing. By carefully timing memory allocation and deallocation operations, the attacker can place controlled data in the freed memory region, effectively hijacking kernel execution flow to achieve arbitrary code execution at SYSTEM privilege level. CVSS vector analysis: the local attack vector (AV:L) means the attacker must already have code execution on the target, but the low attack complexity (AC:L) and low privilege requirement (PR:L) make this a reliable escalation path from any standard user account. The unchanged scope (S:U) indicates the exploit operates within the Windows kernel security boundary, but the high impacts across confidentiality, integrity, and availability (C:H/I:H/A:H) reflect the complete system compromise achievable through SYSTEM-level access. This type of Win32k elevation of privilege vulnerability has been a recurring attack surface in Windows, frequently used in advanced persistent threat (APT) campaigns as a post-exploitation escalation step.
Frequently Asked Questions
Is CVE-2023-29336 being actively exploited?
Yes. CISA has confirmed active exploitation of CVE-2023-29336 in the wild and added it to the Known Exploited Vulnerabilities (KEV) catalog with a remediation deadline of May 30, 2023. Public exploit code is available on Exploit-DB, and the EPSS score of 79.5% indicates a very high probability of ongoing exploitation. The ransomware usage status is currently listed as unknown.
What products are affected by CVE-2023-29336?
CVE-2023-29336 affects Microsoft Windows 10 version 1507, Windows 10 version 1607, Windows Server 2008, Windows Server 2012, and Windows Server 2016. These are primarily older or legacy Windows versions that may still be in use in enterprise environments. Organizations should check the Microsoft advisory for the complete list of affected builds and applicable patches.
How do I fix CVE-2023-29336?
Apply the security updates released by Microsoft in the May 2023 Patch Tuesday that address the Win32k use-after-free vulnerability. Refer to the Microsoft Security Response Center advisory for specific KB articles. If patching is not immediately possible, restrict local logon privileges and deploy endpoint detection solutions to mitigate the risk.
How severe is CVE-2023-29336?
CVE-2023-29336 is rated HIGH with a CVSS 3.1 base score of 7.8. While the local attack vector limits remote exploitation, the low complexity and low privilege requirements make it a reliable escalation path once an attacker has initial access. The EPSS score of 79.5% (99th percentile) confirms very high exploitation activity, and CISA's KEV listing underscores the urgency of remediation.
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