Microsoft Win32k Memory Corruption Vulnerability (CVE-2015-2546)
Published In CISA KEV since Sources: CVE.org
What is affected, what to do
The kernel-mode driver in Microsoft Windows Vista SP2, Windows Server 2008 SP2 and R2 SP1, Windows 7 SP1, Windows 8, Windows 8.1, Windows Server 2012 Gold and R2, Windows RT Gold and 8.1, and Windows 10 allows local users to gain privileges via a crafted application, aka "Win32k Memory Corruption Elevation of Privilege Vulnerability," a different vulnerability than CVE-2015-2511, CVE-2015-2517, and CVE-2015-2518.
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 Server 2008
eq r2..r2 - Microsoft Windows Server 2012
eq r2..r2
- Microsoft Windows Server 2008
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Metrics
8.2
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: Vendor (CNA), CVSS v3
8.2
CVSS v3
Severity High on the scale from 0 to 10.
Source: CVE.org
10.1 %
EPSS score
Elevated — model estimates 10-50% exploitation likelihood.
Source: FIRST EPSS, percentile 95.6
Show all metrics
- Severity
- Critical
Priority (0–325)
The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?
Read in glossary- 239.15 Methodology
Exploit maturity
An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.
Read in glossary- actively exploited
XIEM Effective CVSS
XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.
Read in glossary- 8.2 Methodology
CVSS v3
CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.
Read in glossary- 8.2
EPSS score
The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.
Read in glossary- 10.1 %
- Elevated — model estimates 10-50% exploitation likelihood.
EPSS percentile
The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.
Read in glossary- 95.6
- Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
KEV status
The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.
Read in glossary- Actively exploited
- Published
In CISA KEV since
The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.
Read in glossary- CISA assessment (SSVC)
- Exploitation: active · not automatable · Technical impact: total
- Source: CISA Vulnrichment, as of 14 March 2022
CWE
CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.
Read in glossary- CWE-119
Response and mitigation
Why act now?
Prioritisation rationale
CVE-2015-2546 is a local privilege escalation in the Win32k kernel driver: it needs low-privileged code execution first, but then yields full SYSTEM control with impact crossing the security boundary. Attackers — including ransomware operators per CISA's flag — chain it behind phishing or browser footholds to kill EDR, harvest credentials and move laterally, and exploitation likelihood is rated high. Organisations with long-lived legacy estates (Server 2008/2012, Windows 7 in production and OT environments) and multi-user hosts such as terminal servers are the typical victims. On fully patched modern Windows the residual risk is low; any still-affected host with user interaction or internet access should be treated as high priority and patched or isolated within days.
Runbook step 1
Immediate response (0-24 h)
- Scope affected hosts: Enumerate all systems running Windows Vista SP2, 7 SP1, 8/8.1, RT/RT 8.1, Windows 10 1507, Server 2008 SP2/R2 SP1 and Server 2012/R2 (CMDB, EDR inventory,
Get-ADComputer -Filter * -Properties OperatingSystem). Most of these releases are end-of-life and disproportionately likely to be unpatched. - Deploy the vendor fix: Install Microsoft's Win32k security update for CVE-2015-2546. Patch available from the vendor — look up the KB number per OS build in the vendor advisory (Microsoft Security Update Guide). Verify via
Get-HotFixor WSUS/SCCM compliance reporting. - Isolate unpatchable legacy systems: Move hosts that cannot take the update (e.g. production or OT-adjacent Server 2008) into a dedicated VLAN and restrict inbound SMB (445/tcp), RDP (3389/tcp) and WinRM (5985/5986/tcp) to named jump hosts only.
- Hunt on exposed hosts first: On terminal servers, Citrix/RDS hosts and internet-facing workstations, hunt for unexpected SYSTEM processes with a user-context parent (see Detection rules). On a hit: isolate, capture memory, and reset local and domain credentials of every account that logged on there.
- Ransomware readiness: CISA flags known ransomware use — validate offline backups of affected servers for integrity and restorability today.
- Scope affected hosts: Enumerate all systems running Windows Vista SP2, 7 SP1, 8/8.1, RT/RT 8.1, Windows 10 1507, Server 2008 SP2/R2 SP1 and Server 2012/R2 (CMDB, EDR inventory,
Runbook step 2
Mitigation layers
- Application control (endpoint hardening): Enforce WDAC or AppLocker rules that block execution from user-writable paths (
%TEMP%,%APPDATA%,%USERPROFILE%\Downloads,C:\Users\Public). The exploit requires a crafted binary to run locally — deny the execution and the escalation path disappears. - Close the initial-access vector: Block internet-sourced Office macros via GPO and set Defender ASR rules "Block Office applications from creating child processes" and "Block executable content from email client and webmail" to Block mode; this bug is almost always chained after phishing-based initial access.
- Least privilege (IAM): Remove local admin rights, roll out LAPS, and prevent Tier 0 domain accounts from logging on to unpatched clients or terminal servers so a local SYSTEM escalation does not become domain compromise.
- Network segmentation: Block workstation-to-workstation SMB/RDP with host firewall rules to limit lateral movement. Restrict outbound internet from legacy servers to an allow-list via proxy.
- Credential protection: Where the OS supports it, enable LSA protection (
RunAsPPL) and Credential Guard to hinder LSASS dumping after successful escalation. - Lifecycle: For out-of-support systems, document a migration plan with formal management risk acceptance (NIS2 risk-management obligation).
- Application control (endpoint hardening): Enforce WDAC or AppLocker rules that block execution from user-writable paths (
Runbook step 3
Detection rules
- Sysmon EID 1 / Security 4688 — integrity jump: Process running as
NT AUTHORITY\SYSTEM/IntegrityLevel=Systemwhose parent runs under a regular user (e.g. SYSTEMcmd.exe/powershell.exedescending fromexplorer.exe). KQL:DeviceProcessEvents | where ProcessIntegrityLevel == "System" and InitiatingProcessIntegrityLevel in ("Medium","Low") and InitiatingProcessAccountName !~ "system" - Execution from user paths: Sysmon EID 1 with
Imageunder\AppData\,\Temp\or\Users\Public\, followed within seconds by a SYSTEM child process — classic Win32k exploit-loader pattern. - Kernel crashes as failed-attempt signal: System Event ID 1001 (BugCheck) or 41 referencing
win32k.syson hosts with no recent driver changes; clustered BSODs right after an unknown binary runs suggest failed exploitation. - Post-escalation activity: Security 4720/4732 (new local account / added to Administrators), 7045 (new service), and Sysmon EID 10 with
TargetImage=lsass.exefrom an unusual source process. SPL:index=wineventlog EventCode=7045 | stats count by ComputerName, Service_File_Name - EDR process ancestry: Model
winword.exe/outlook.exe→ unknown EXE →cmd.exe(SYSTEM) as a Sigma rule: "ancestry contains Office process AND target token is SYSTEM".
- Sysmon EID 1 / Security 4688 — integrity jump: Process running as
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
The kernel-mode driver in Microsoft Windows Vista SP2, Windows Server 2008 SP2 and R2 SP1, Windows 7 SP1, Windows 8, Windows 8.1, Windows Server 2012 Gold and R2, Windows RT Gold and 8.1, and Windows 10 allows local users to gain privileges via a crafted application, aka "Win32k Memory Corruption Elevation of Privilege Vulnerability," a different vulnerability than CVE-2015-2511, CVE-2015-2517, and CVE-2015-2518.
Source: CISA KEV Catalog, cvelistv5, NVD (NIST), CVE.org (MITRE)
Vendors and products
- Microsoft Windows 10 1507
- Microsoft Microsoft Windows 7
- Microsoft Microsoft Windows 8 Professional Edition
- Microsoft Microsoft Windows 8.1
- Microsoft Microsoft Windows RT Gold
- Microsoft Microsoft Windows RT 8.1
- Microsoft Microsoft Windows Server 2008
- Microsoft Microsoft Windows Server 2012
- Microsoft Microsoft Windows Vista Gold on X64
Affected operating systems
| Windows | microsoft | windows_10_1507 | — |
| Windows | microsoft | windows_7 | — |
| Windows | microsoft | windows_8 | — |
| Windows | microsoft | windows_8.1 | — |
| Windows | microsoft | windows_rt | — |
| Windows | microsoft | windows_rt_8.1 | — |
| Windows | microsoft | windows_server_2008 | r2 |
| Windows | microsoft | windows_server_2008 | — |
| Windows | microsoft | windows_server_2012 | r2 |
| Windows | microsoft | windows_server_2012 | — |
| Windows | microsoft | windows_vista | — |
Weakness classes (CWE)
CWE-119Improper Restriction of Operations within the Bounds of a Memory Buffer
Class
The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.
Entry at MITRE CWE-119
Public exploit references
Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.
| CISA KEV Catalog | CISA Known Exploited Vulnerability (opens in a new tab)cisa.gov | actively exploited |
References & sources
- securitytracker.com1033485Vulnerability database, x_refsource_SECTRACK
- docs.microsoft.comMS15-097Vendor advisory, x_refsource_MS
- securityfocus.com76608Vulnerability database, x_refsource_BID
- cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2015-2546government-resource
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<a href="https://intel.neosec.eu/en/cve/CVE-2015-2546"><img src="https://intel.neosec.eu/badge/cve/CVE-2015-2546.svg?lang=en" alt="CVE-2015-2546 – NEOSEC Intel" height="20"></a>