Microsoft Win32k Privilege Escalation Vulnerability (CVE-2015-1701)

What is affected, what to do

Win32k.sys in the kernel-mode drivers in Microsoft Windows Server 2003 SP2, Vista SP2, and Server 2008 SP2 allows local users to gain privileges via a crafted application, as exploited in the wild in April 2015, aka "Win32k Elevation of Privilege Vulnerability."

The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. The available sources name no fixed version. Check the vendor guidance in the references below. Immediate actions, mitigation and detection rules are in the runbook below.

Affected

• Microsoft Windows 2003 Server R2 Service Pack 2 eq r2..r2

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Metrics

Response and mitigation

1. 01

   Runbook step 1

   Immediate response (0-24 h)

   • Inventory legacy hosts: Pull every Windows Server 2003 SP2, Vista SP2, Windows 7 and Server 2008 SP2 system from the CMDB, AD (Get-ADComputer -Filter * -Properties OperatingSystem | ? OperatingSystem -match "2003|2008|Vista|Windows 7") and network scans. All of these platforms are end-of-life, so treat each hit as a documented risk exception.
   • Verify and apply the security update: A patch is available from the vendor. Look up the exact KB number in the Microsoft advisory for CVE-2015-1701. Confirm installation with Get-HotFix or wmic qfe list against that KB, and escalate any host that is missing it.
   • Isolate unpatchable systems: For hosts that cannot be updated (production lines, niche line-of-business software), cut interactive logons to the bare minimum. Allow RDP (TCP 3389) and SMB (TCP 445) only from a dedicated admin network.
   • Compromise assessment where indicated: This bug is chained after initial access, such as phishing, a browser exploit or stolen credentials. On legacy hosts showing signs of foreign code, rotate local admin and service account passwords. If the host is domain-joined, treat cached domain credentials as exposed.
   • Ransomware readiness: For every affected server, confirm that offline or immutable backups exist and actually restore.
2. 02

   Runbook step 2

   Mitigation layers

   • Network segmentation: Move legacy systems into a dedicated VLAN or zone. Apply default-deny egress to the internet and allow only required destinations. Block lateral connections into client networks (SMB, RDP, WinRM 5985/5986).
   • Application control: Block execution of unknown binaries from user-writable paths, including %TEMP%, %APPDATA%, C:\Users\Public and Downloads. Use AppLocker on Windows 7/Server 2008 R2 and Software Restriction Policies on older builds. The attack requires a locally launched crafted application, so this control blocks it directly.
   • IAM/least privilege: Use GPO to deny interactive and RDP logon rights to standard users on servers. Prioritise migrating any shared legacy terminal servers.
   • Endpoint hardening: Deploy an EDR/AV agent with kernel-exploit protection where the vendor still supports the legacy OS. Add publicly available PoC tooling for this CVE to signature and hash blocklists.
   • Strategic fix: Record a dated migration or decommissioning plan for EoL systems in the risk register. Under NIS2, an unpatched EoL host without compensating controls is not defensible.
3. 03

   Runbook step 3

   Detection rules

   • Process creation with an integrity jump (Event ID 4688, Vista/2008 onward): Look for a process running as NT AUTHORITY\SYSTEM whose parent ran as a standard user. A typical example is cmd.exe or powershell.exe as SYSTEM, spawned by a binary in %TEMP%. On Server 2003 the equivalent is Event ID 592. Process-tracking audit policy must be enabled first.
   • Sysmon EID 1 (where a supported Sysmon version runs): Sigma shape: selection: IntegrityLevel: System, User|contains: 'SYSTEM', ParentImage|contains: ['\AppData\','\Temp\','\Users\Public\'] with condition: selection.
   • EDR process ancestry: Watch for the chain user process (e.g. winword.exe, a browser, an unknown EXE) → unknown binary → cmd.exe/net.exe/whoami.exe running as SYSTEM. KQL: DeviceProcessEvents | where AccountName =~ "system" and InitiatingProcessAccountName !~ "system" and InitiatingProcessFolderPath has_any ("\\temp\\","\\appdata\\").
   • Post-escalation follow-on activity: Event IDs 4720/4732 (new account or addition to local Administrators), 7045 (new service) and access to lsass.exe. vssadmin delete shadows is a strong ransomware precursor.
   • Network telemetry (Zeek/Suricata): Flag new outbound internet connections from legacy servers and unusual SMB/RDP from the legacy zone. This is often the only reliable source when no modern agent runs on the old hosts.

Detection rules

No NEOSEC detection rule is available for this vulnerability yet.

Classification under NIS2 and CRA

Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

NIS2

NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

Read in glossary

Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).

CRA

The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

Read in glossary

Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.

ISO/IEC 27001

ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

Read in glossary

Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

Description

Win32k.sys in the kernel-mode drivers in Microsoft Windows Server 2003 SP2, Vista SP2, and Server 2008 SP2 allows local users to gain privileges via a crafted application, as exploited in the wild in April 2015, aka "Win32k Elevation of Privilege Vulnerability."

Source: cvelistv5, CISA KEV Catalog, NVD (NIST), CVE.org (MITRE)

Vendors and products

• Microsoft Microsoft Windows 2003 Server R2 Service Pack 2
• Microsoft Microsoft Windows 7
• Microsoft Microsoft Windows Server 2008
• Microsoft Microsoft Windows Vista Gold on X64

References & sources

• twitter.comsymantec/statuses/590208710527549440x_refsource_MISC
• exploit-db.com37049Exploit, x_refsource_EXPLOIT-DB
• securityfocus.com74245Vulnerability database, x_refsource_BID
• docs.microsoft.comMS15-051Vendor advisory, x_refsource_MS
• exploit-db.com37367Exploit, x_refsource_EXPLOIT-DB
• fireeye.comblog/threat-research/2015/04/probable_apt28_useo.htmlx_refsource_MISC
• securitytracker.com1032155Vulnerability database, x_refsource_SECTRACK
• seclists.org20200514 KL-001-2020-002 : Cellebrite Restricted Desktop Escape and Escalation of User PrivilegeMailing list, x_refsource_FULLDISC
• cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2015-1701government-resource