CVE-2018-8453
Microsoft Win32k Privilege Escalation Vulnerability
Description
CVE-2018-8453 is a HIGH severity privilege escalation vulnerability in the Microsoft Windows Win32k component, which handles kernel-mode graphics operations. The vulnerability allows a local attacker to escalate privileges by exploiting improper handling of objects in memory within the Win32k kernel driver. With a CVSS 3.1 score of 7.8, successful exploitation grants SYSTEM-level privileges on the affected Windows host. The vulnerability affects a wide range of Windows versions including Windows 7, Windows 8.1, Windows 10 (multiple builds), and Windows Server editions from 2008 through 2019. CISA added CVE-2018-8453 to its KEV catalog on January 21, 2022, and confirmed its association with ransomware campaigns. The EPSS score of 0.78167 (98.99th percentile) reflects very high exploitation probability, consistent with its use in advanced persistent threat (APT) campaigns and ransomware operations.
KEV Information
CVSS Score
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:HOpen in CalculatorAffected Products
| Vendor | Product | Version |
|---|---|---|
| microsoft | windows 10 1507 | - |
| microsoft | windows 10 1607 | - |
| microsoft | windows 10 1703 | - |
| microsoft | windows 10 1709 | - |
| microsoft | windows 10 1803 | - |
| microsoft | windows 10 1809 | - |
| microsoft | windows 7 | - |
| microsoft | windows 8.1 | - |
| microsoft | windows rt 8.1 | - |
| microsoft | windows server 1709 | - |
| microsoft | windows server 1803 | - |
| microsoft | windows server 2008 | -; r2 |
| microsoft | windows server 2012 | -; r2 |
| microsoft | windows server 2016 | - |
| microsoft | windows server 2019 | - |
Multiple CVSS Assessments
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
References
- http://packetstormsecurity.com/files/153669/Microsoft-Windows-NtUserSetWindowFNID-Win32k-User-Callback.html(Exploit, Third Party Advisory, VDB Entry)
- http://www.securityfocus.com/bid/105467(Broken Link, Third Party Advisory, VDB Entry)
- http://www.securitytracker.com/id/1041828(Broken Link, Third Party Advisory, VDB Entry)
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2018-8453(Patch, Vendor Advisory)
- https://securelist.com/cve-2018-8453-used-in-targeted-attack(Exploit, Technical Description, Third Party Advisory)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2018-8453(US Government Resource)
Weakness Type
Win32k Kernel-Mode Privilege Escalation
CVE-2018-8453 is a kernel-mode privilege escalation vulnerability in the Win32k component of Microsoft Windows. Win32k (win32k.sys) is a kernel-mode driver that handles the Windows graphics subsystem, including window management, display output, and input processing. Due to its complexity and the large number of system calls it exposes, Win32k has historically been one of the most frequent sources of local privilege escalation vulnerabilities in Windows.
The vulnerability specifically involves improper handling of objects in memory within Win32k's callback mechanisms. The Win32k driver processes user-mode callback functions during certain window management operations, and the vulnerability arises when the driver fails to properly validate or track object state changes that occur during these callbacks. An attacker can craft a specially designed application that triggers specific callback sequences, causing the Win32k driver to use a kernel object in an inconsistent state. This can lead to a use-after-free or type confusion condition in kernel memory, which the attacker leverages to execute arbitrary code with kernel-level (SYSTEM) privileges. The vulnerability was discovered being exploited in the wild by Kaspersky Lab, who attributed the exploitation to the FruityArmor APT group. Learn more about Win32k vulnerabilities
Impact Analysis
CVE-2018-8453 carries a CVSS 3.1 base score of 7.8 (HIGH) with local privilege escalation characteristics.
Confidentiality (High): Successful exploitation elevates the attacker to SYSTEM-level privileges on the Windows host. SYSTEM is the highest privilege level in Windows, providing unrestricted access to all data on the system including SAM database password hashes, LSASS process memory containing cached domain credentials, DPAPI master keys, certificate private keys, and all user data. In domain-joined environments, SYSTEM access enables extraction of Kerberos ticket-granting tickets and other authentication tokens for lateral movement.
Integrity (High): With SYSTEM privileges, the attacker has unrestricted ability to modify any file, registry key, or system configuration on the host. This enables installation of rootkits that hide in the kernel, modification of boot configuration to persist across reboots, tampering with security event logs to conceal the intrusion, and modification of security software configurations to disable endpoint protection. The kernel-level access also allows direct manipulation of process memory for other running applications.
Availability (High): SYSTEM-level access allows complete control over the operating system, including the ability to terminate any process, disable critical services, encrypt the filesystem with ransomware, or cause a kernel-level crash resulting in a Blue Screen of Death (BSOD). The confirmed ransomware association demonstrates that this availability impact has materialized in real-world attacks.
Scope (Unchanged): The scope remains within the Windows host system. However, SYSTEM-level access on a domain-joined machine enables numerous lateral movement techniques that extend the practical impact well beyond the initially compromised host. The EPSS score of 0.78167 (98.99th percentile) confirms that this vulnerability is among the top 1% most exploited CVEs.
Exploit Maturity
Active Exploitation: CVE-2018-8453 was discovered being actively exploited as a zero-day by the FruityArmor APT group before Microsoft released a patch. Kaspersky Lab identified the exploitation in targeted attacks and reported it to Microsoft. CISA added the vulnerability to the KEV catalog on January 21, 2022, confirming continued exploitation beyond the initial APT campaigns.
Ransomware Association: CISA's KEV catalog explicitly confirms that CVE-2018-8453 is associated with known ransomware campaigns. The privilege escalation from a standard user to SYSTEM is a critical step in ransomware attack chains, enabling the attacker to disable security software, access all files on the system, and deploy ransomware with the highest possible permissions.
Public Exploits: Detailed exploit analysis is available from Kaspersky's Securelist, documenting the Win32k NtUserSetWindowFNID user callback exploitation. Additional public exploit code is available on Packet Storm Security. Microsoft's patch details are documented in the MSRC advisory.
EPSS Context: The EPSS score of 0.78167 (98.99th percentile) places this in the top 1% of all CVEs for exploitation probability. The combination of APT-grade exploitation, ransomware association, and public exploit availability drives this exceptionally high score.
KEV Deadline: The CISA remediation deadline was July 21, 2022. Given the ransomware association, all organizations should ensure this patch is applied across all affected Windows systems.
Remediation
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Apply the Microsoft security update for CVE-2018-8453 immediately. Install the October 2018 security update (or later cumulative update) from the Microsoft Security Response Center through Windows Update or WSUS. This patch corrects the Win32k kernel driver's handling of objects during user-mode callback processing.
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Prioritize patching based on ransomware risk. Due to the confirmed ransomware association, give highest priority to systems that store critical data, run customer-facing services, or serve as stepping stones for lateral movement (such as domain controllers, jump servers, and administrative workstations).
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Deploy endpoint detection and response (EDR) solutions. Modern EDR platforms can detect kernel-mode exploitation attempts, including the specific callback abuse patterns associated with Win32k privilege escalation. Ensure EDR agents are deployed and configured to alert on suspicious Win32k activity and privilege escalation indicators.
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Implement application execution controls. Since exploitation requires running a specially crafted application, application control policies (AppLocker, Windows Defender Application Control) that restrict which executables can run significantly reduce the risk. Prevent execution of unsigned or untrusted applications in user-accessible directories.
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Audit systems for indicators of compromise. Search for signs of FruityArmor or other APT tooling, unexpected SYSTEM-level processes, modifications to kernel driver files, and evidence of credential harvesting. Kaspersky's research provides specific IOCs associated with the original exploitation campaign.
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Enforce least privilege for user accounts. Ensure users operate with standard (non-administrative) accounts for daily tasks. While the vulnerability escalates to SYSTEM regardless of the starting privilege level, limiting initial access makes it harder for attackers to reach the point of exploitation in a multi-stage attack chain.
Technical Details
CVE-2018-8453 is a local privilege escalation vulnerability in the Windows Win32k kernel-mode driver (win32k.sys). The vulnerability resides in the handling of the NtUserSetWindowFNID system call, which manages window function ID assignments. During the processing of certain window management operations, Win32k invokes user-mode callback functions while holding references to kernel objects.
The exploitation technique involves creating a specially crafted application that manipulates window objects and their associated callback functions to trigger an inconsistent kernel state. Specifically, the attacker triggers a user-mode callback during NtUserSetWindowFNID processing, and within the callback, performs operations that alter the state of kernel objects that Win32k still references. When the callback returns and Win32k continues processing with the now-stale object references, a use-after-free or type confusion condition occurs in kernel memory.
The CVSS vector (AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H) indicates local access is required along with some user interaction, but no privileges are needed. The user interaction component reflects the need for a user to open a malicious document or run an application, though in targeted attack scenarios, this is readily achieved through social engineering.
The attacker leverages the kernel memory corruption to overwrite critical kernel data structures, ultimately gaining the ability to execute arbitrary code at Ring 0 (kernel level). The Kaspersky analysis documented the complete exploitation chain used by FruityArmor, including heap grooming to control the layout of kernel pool allocations, the specific callback manipulation sequence, and the final privilege escalation from the corrupted kernel state to SYSTEM-level code execution. The exploit was noted for its sophistication, using advanced techniques to achieve reliable exploitation across multiple Windows versions.
Frequently Asked Questions
What is CVE-2018-8453?
CVE-2018-8453 is a privilege escalation vulnerability in the Microsoft Windows Win32k kernel-mode driver. It allows a local attacker to exploit improper object handling during user-mode callbacks to gain SYSTEM-level privileges. The vulnerability was discovered being exploited as a zero-day by the FruityArmor APT group and has confirmed associations with ransomware campaigns. It carries a CVSS 3.1 score of 7.8 (HIGH).
Which Windows versions are affected by CVE-2018-8453?
CVE-2018-8453 affects a broad range of Windows versions including Windows 7, Windows 8.1, Windows 10 (builds 1507, 1607, 1703, 1709, 1803, and 1809), Windows Server 2008, Windows Server 2008 R2, Windows Server 2012, Windows Server 2012 R2, Windows Server 2016, Windows Server 2019, and various Windows Server Semi-Annual Channel releases. All 32-bit and 64-bit versions of these operating systems are affected.
How do I fix CVE-2018-8453?
Apply the October 2018 cumulative security update or later through Windows Update. Microsoft's patch corrects the Win32k driver's object handling during user-mode callbacks. After patching, deploy EDR solutions capable of detecting kernel exploitation attempts, implement application execution controls, and audit systems for signs of prior compromise, particularly indicators associated with the FruityArmor APT group.
How severe is CVE-2018-8453?
CVE-2018-8453 is rated HIGH with a CVSS score of 7.8. Its EPSS score of 0.78167 (98.99th percentile) confirms it is among the top 1% most exploited vulnerabilities. It was initially exploited as a zero-day by the FruityArmor APT group and has been subsequently adopted by ransomware operators. CISA has confirmed the ransomware association and included it in the Known Exploited Vulnerabilities catalog, underscoring its real-world danger.
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