CVE-2015-1701

CVE-2015-1701: Win32k.sys Local Privilege Escalation Exploited by APT28

AI-generated analysis based on the vulnerability data on this page.

Summary

CVE-2015-1701 is a local privilege escalation vulnerability residing in the Win32k.sys kernel-mode driver on multiple Microsoft Windows platforms. The flaw enables an authenticated local attacker to execute arbitrary code with elevated privileges, potentially taking full control of the affected system. This vulnerability was actively exploited in the wild beginning April 2015 and has been attributed to targeted threat actor activity.

Background

Win32k.sys is the kernel-mode component responsible for window management, graphics rendering, and user-interface operations in the Windows operating system. Because it runs in kernel space, any vulnerability within this driver can provide a direct path to escalating privileges from a standard user to SYSTEM-level access. CVE-2015-1701 was disclosed by Microsoft in security bulletin MS15-051 and was rapidly incorporated into exploit kits and targeted campaigns following public disclosure.

Root Cause

The specific root cause has not been publicly assigned a CWE identifier in available records. The vulnerability stems from improper handling of objects in memory within Win32k.sys, allowing an attacker to manipulate kernel structures and execute arbitrary code in kernel context. The issue reflects a class of kernel object-management weaknesses that can arise when pointer or handle validation is insufficient during window-message processing or graphics operations.

Impact

The vulnerability is rated HIGH severity. On CVSS 3.1, it scores 7.8 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H), reflecting that a low-privileged local attacker can achieve high confidentiality, integrity, and availability impacts without user interaction. The CVSS 2.0 vector is AV:L/AC:L/Au:N/C:C/I:C/A:C with a base score of 7.2. Successful exploitation grants complete control over the target system, including the ability to install programs, modify data, and create new accounts with full administrative rights.

Exploitation Walkthrough

Ethics caveat: This section describes the vulnerability at a defensive level only. No working exploit code is provided, and the details are intended to aid detection and mitigation rather than enable unauthorized access.

An attacker with local access and standard user privileges can trigger the vulnerability by interacting with the Win32k subsystem through a crafted application. The exploitation path typically involves:

1. Triggering the flawed code path: The attacker application invokes specific graphics or window-management API calls that reach the vulnerable function in Win32k.sys.
2. Kernel memory corruption: Improper object handling leads to a use-after-free or out-of-bounds condition, allowing the attacker to corrupt kernel memory structures.
3. Privilege escalation: By controlling the corrupted kernel object, the attacker redirects execution to attacker-controlled code running in kernel mode, effectively escalating to SYSTEM privileges.

This vulnerability was observed in targeted attacks in April 2015. According to public reporting, the exploit was used in conjunction with a separate remote-code-execution vulnerability to compromise systems and maintain persistence. The combination of an RCE with a local privilege escalation is a common pattern in advanced threat campaigns, allowing initial access to be converted into full administrative control.

Affected and Patched Versions

The following products are confirmed vulnerable based on published CPE data:

• Microsoft Windows Server 2003 SP2
• Microsoft Windows Server 2003 R2 SP2
• Microsoft Windows Vista SP2
• Microsoft Windows Server 2008 SP2
• Microsoft Windows 7 SP1

Microsoft addressed this vulnerability in security bulletin MS15-051, released in May 2015. Administrators should apply the corresponding updates for their supported platforms. Note that Windows Server 2003 and Windows Vista have reached end-of-life and no longer receive security updates from Microsoft; systems still running these versions should be treated as high-risk and prioritized for migration or isolation.

Remediation

1. Apply patches: For supported platforms, install the updates provided in Microsoft Security Bulletin MS15-051.
2. Upgrade or decommission: Migrate Windows Server 2003, Windows Vista, and other end-of-life systems to supported operating systems. Where migration is not immediately feasible, isolate these systems behind strict network segmentation and remove internet-facing exposure.
3. Compensating controls:
   • Restrict local user access on sensitive systems to reduce the attack surface.
   • Enable and monitor application-execution policies (e.g., AppLocker or Windows Defender Application Control) to prevent unauthorized binaries from running.
   • Maintain up-to-date endpoint protection with behavioral monitoring capabilities to catch anomalous kernel activity.

Detection

Defenders should monitor for indicators of exploitation, including:

• Unexpected Win32k.sys crashes or bug-check events (blue screens) on endpoints, which may indicate failed exploitation attempts.
• Anomalous process creation where a low-integrity process suddenly spawns a high-integrity or SYSTEM-level process.
• Suspicious API call sequences targeting NtUserMessageCall, NtUserSetWindowLong, or related undocumented Win32k interfaces from non-standard executables.
• Endpoint detection and response (EDR) alerts for kernel memory tampering or privilege-escalation techniques such as token manipulation.

Assessment

CVE-2015-1701 carries an EPSS score of 0.562 (98.93rd percentile), indicating a very high probability of exploitation in the wild. It is also listed in the CISA Known Exploited Vulnerabilities (KEV) catalog with a known exploitation date of 2022-03-03, and it appears in the EU exploited vulnerabilities database (EUVD-2015-1831). These indicators confirm that threat actors have historically weaponized and continue to target this flaw.

Key lessons:

• Kernel driver hygiene remains critical: Vulnerabilities in core graphics and window-management drivers continue to be attractive targets because they offer reliable, high-impact privilege escalation.
• End-of-life systems are persistent liabilities: Organizations still running Windows Server 2003 or Vista lack patching as a remediation option, making migration and isolation the only viable defenses.

References

• https://docs.microsoft.com/en-us/security-updates/securitybulletins/2015/ms15-051
• https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2015-1701
• https://www.fireeye.com/blog/threat-research/2015/04/probable_apt28_useo.html
• https://www.exploit-db.com/exploits/37049/
• https://www.exploit-db.com/exploits/37367/
• http://www.securityfocus.com/bid/74245
• http://www.securitytracker.com/id/1032155
• http://seclists.org/fulldisclosure/2020/May/34
• http://twitter.com/symantec/statuses/590208710527549440