Microsoft Win32k Privilege Escalation Vulnerability (CVE-2016-7255)
Published Last modified In CISA KEV since Sources: CVE.org
What is affected, what to do
The kernel-mode drivers in Microsoft Windows Vista SP2, Windows Server 2008 SP2 and R2 SP1, Windows 7 SP1, Windows 8.1, Windows Server 2012 Gold and R2, Windows RT 8.1, Windows 10 Gold, 1511, and 1607, and Windows Server 2016 allow local users to gain privileges via a crafted application, 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 Server 2008
eq r2..r2 - Microsoft Windows Server 2012
eq r2..r2
- Microsoft Windows Server 2008
Not sure whether and how you are affected? Ask a question about this vulnerability
Metrics
7.8
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: NVD, CVSS v3
7.8
CVSS v3
Severity High on the scale from 0 to 10.
Source: CVE.org
81.0 %
EPSS score
High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
Source: FIRST EPSS, percentile 99.63
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- 243.41 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- 7.8 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- 7.8
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- 81.0 %
- High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
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- 99.63
- 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 5 March 2021
Response and mitigation
Why act now?
Prioritisation rationale
CVE-2016-7255 is a textbook local privilege-escalation building block. Attackers typically gain initial access through phishing or a browser or plugin exploit, then use this flaw to reach kernel/SYSTEM privileges so they can evade EDR, steal credentials and move laterally. CISA flags it as used in ransomware campaigns, and its exploitation likelihood is very high. Because the fix has been available since 2016, real-world risk is concentrated in organisations with legacy estates such as OT-adjacent clients, line-of-business servers on Server 2008, or terminal servers. Rate it critical wherever such hosts exist; on a fully patched fleet it is mainly a compliance check under NIS2 and ISO 27001 A.8.8.
Runbook step 1
Immediate response (0-24 h)
- Verify patch level: Query Intune, SCCM/MECM, WSUS or your EDR for hosts running Windows Vista SP2, 7 SP1, 8.1, RT 8.1, 10 (1507/1511/1607), Server 2008 SP2/R2 SP1, 2012/2012 R2 and 2016 that are missing updates. A Microsoft security update for CVE-2016-7255 is available; look up the KB number for each OS in the Microsoft Security Update Guide. Any current cumulative update or Monthly Rollup also closes the gap.
- Prioritise legacy hosts: Windows 7, Server 2008/2008 R2 and Windows 10 1507/1511/1607 are out of support. If any of them is still missing a 2016 update, treat it as evidence of a systemic patch-management gap. Patch these hosts now or move them into an isolated segment, and put them on a migration plan.
- Start with multi-user systems: RDS/terminal servers, Citrix workers, jump hosts and kiosks are the most exposed, because many low-privileged users can run arbitrary code there.
- Compromise check: On unpatched hosts with suspicious activity (phishing hits, malware alerts), hunt for SYSTEM processes spawned from user-context parents (see Detection rules). If you get a hit, isolate the host, treat local and cached credentials as burned, and reset passwords and Kerberos keys for every account that was logged on.
- Close the initial access vector: Exploitation requires local code execution. In practice the bug is chained with a browser, Office or phishing payload, so also patch browsers, Office and PDF readers, and block macros via GPO.
Runbook step 2
Mitigation layers
- Application control: Run WDAC or AppLocker in enforce mode and block execution from
%TEMP%,%APPDATA%,Downloadsand any other user-writable path. The exploit needs a crafted binary or DLL load, so allowlisting removes its foothold. - Reduce the Win32k attack surface (Windows 10/Server 2016): Use Exploit Protection or
Set-ProcessMitigationto apply "Disable Win32k system calls" to processes that have no GUI. Keep Edge and Office components running with their sandbox profiles enabled. - Network segmentation: Place unpatchable legacy hosts in a dedicated VLAN. Allow RDP (3389/tcp) and SMB (445/tcp) only from admin jump hosts, and restrict outbound internet access to proxy allowlists. This keeps a SYSTEM-level foothold contained to the local host.
- Least privilege and credential protection: Remove local admin rights, deploy LAPS, and enable Credential Guard or LSA protection (
RunAsPPL). After escalating, an attacker then cannot simply harvest domain credentials from LSASS. - EDR hardening: Set the ASR rules "Block credential stealing from LSASS", "Block Office applications from creating child processes" and "Block executable files unless they meet prevalence/age criteria" to block mode.
- Application control: Run WDAC or AppLocker in enforce mode and block execution from
Runbook step 3
Detection rules
- Sysmon EID 1 / Security 4688: A process running at
IntegrityLevel: Systemor asNT AUTHORITY\SYSTEMwhose parent runs as a normal user at Medium or Low integrity. A typical pattern iscmd.exeorpowershell.exeas SYSTEM under an unknown binary in%TEMP%. Sigma shape:selection: IntegrityLevel: System AND ParentUser|not: 'NT AUTHORITY\SYSTEM' AND ParentImage|not: (services.exe, wininit.exe, svchost.exe). - Defender for Endpoint (KQL):
DeviceProcessEvents | where ProcessIntegrityLevel == "System" and InitiatingProcessIntegrityLevel in ("Medium","Low") and InitiatingProcessAccountSid != "S-1-5-18" - Process ancestry:
winword.exe/excel.exe/browser → unsigned EXE orrundll32.exe→ SYSTEM shell. This is often followed shortly by LSASS access (Sysmon EID 10,TargetImage: lsass.exe,GrantedAccess: 0x1010/0x1410). - Security 4672 (special privileges assigned): Look for this event on non-admin accounts, or
SeDebugPrivilegein an interactive user session. Then check for new services (7045) or scheduled tasks (4698) as persistence indicators. - Splunk (SPL):
index=sysmon EventCode=1 IntegrityLevel=System NOT ParentUser="NT AUTHORITY\\SYSTEM" | stats count by host, ParentImage, Image, User
- Sysmon EID 1 / Security 4688: A process running at
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 drivers in Microsoft Windows Vista SP2, Windows Server 2008 SP2 and R2 SP1, Windows 7 SP1, Windows 8.1, Windows Server 2012 Gold and R2, Windows RT 8.1, Windows 10 Gold, 1511, and 1607, and Windows Server 2016 allow local users to gain privileges via a crafted application, aka "Win32k Elevation of Privilege Vulnerability."
Source: cvelistv5, NVD (NIST), CISA KEV Catalog, CVE.org (MITRE)
Vendors and products
- Microsoft Windows 10 1507
- Microsoft Windows 10 1511
- Microsoft Microsoft Windows 10 1607
- Microsoft Microsoft Windows 7
- Microsoft Microsoft Windows 8.1
- Microsoft Microsoft Windows RT 8.1
- Microsoft Microsoft Windows Server 2008
- Microsoft Microsoft Windows Server 2012
- Microsoft Microsoft Windows Server 2016
- Microsoft Microsoft Windows Vista Gold on X64
Affected operating systems
| Windows | microsoft | windows_10_1507 | — |
| Windows | microsoft | windows_10_1511 | — |
| Windows | microsoft | windows_10_1607 | — |
| Windows | microsoft | windows_7 | — |
| Windows | microsoft | windows_8.1 | — |
| 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_server_2016 | — |
| Windows | microsoft | windows_vista | — |
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 | |
| GitHub | mwrlabs/CVE-2016-7255 (opens in a new tab)github.com | PoC (publicly reported)reported, not verified | — |
| Packet Storm | Microsoft Windows Kernel win32k.sys NtSetWindowLongPtr Privilege Escalation (opens in a new tab)packetstormsecurity.com | PoC (publicly reported)reported, not verified | — |
| Exploit-DB | EDB-ID 40745 (opens in a new tab)exploit-db.com | PoC (publicly reported)reported, not verified | — |
| Exploit-DB | EDB-ID 40823 (opens in a new tab)exploit-db.com | PoC (publicly reported)reported, not verified | — |
| Exploit-DB | EDB-ID 41015 (opens in a new tab)exploit-db.com | PoC (publicly reported)reported, not verified | — |
References & sources
- packetstormsecurity.comfiles/140468/Microsoft-Windows-Kernel-win32k.sys-NtSetWindowLon…x_refsource_MISC
- github.commwrlabs/CVE-2016-7255x_refsource_MISC
- exploit-db.com40823Exploit, x_refsource_EXPLOIT-DB
- exploit-db.com41015Exploit, x_refsource_EXPLOIT-DB
- securingtomorrow.mcafee.commcafee-labs/digging-windows-kernel-privilege-escalation-vulnera…x_refsource_MISC
- exploit-db.com40745Exploit, x_refsource_EXPLOIT-DB
- securitytracker.com1037251Vulnerability database, x_refsource_SECTRACK
- docs.microsoft.comMS16-135Vendor advisory, x_refsource_MS
- blog.trendmicro.comtrendlabs-security-intelligence/one-bit-rule-system-analyzing-c…x_refsource_MISC
- securityfocus.com94064Vulnerability database, x_refsource_BID
- security.googleblog.com2016/10/disclosing-vulnerabilities-to-protect.htmlx_refsource_MISC
- cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2016-7255government-resource
Changes to this CVE
Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).
Record modifiedMicrosoft
New references:- http://blog.trendmicro.com/trendlabs-security-intelligence/one-bit-rule-system-analyzing-cve-2016-7255-exploit-wild/
- http://packetstormsecurity.com/files/140468/Microsoft-Windows-Kernel-win32k.sys-NtSetWindowLongPtr-Privilege-Escalation.html
- http://www.securityfocus.com/bid/94064
- http://www.securitytracker.com/id/1037251
and 7 more references
Show 33 original changes
Individual changes of this event as published by NVD Type Action Before After Reference added —http://blog.trendmicro.com/trendlabs-security-intelligence/one-bit-rule-system-analyzing-cve-2016-7255-exploit-wild/Reference added —http://packetstormsecurity.com/files/140468/Microsoft-Windows-Kernel-win32k.sys-NtSetWindowLongPtr-Privilege-Escalation.htmlReference added —http://www.securityfocus.com/bid/94064Reference added —http://www.securitytracker.com/id/1037251Reference added —https://docs.microsoft.com/en-us/security-updates/securitybulletins/2016/ms16-135Reference added —https://github.com/mwrlabs/CVE-2016-7255Reference added —https://securingtomorrow.mcafee.com/mcafee-labs/digging-windows-kernel-privilege-escalation-vulnerability-cve-2016-7255/Reference added —https://security.googleblog.com/2016/10/disclosing-vulnerabilities-to-protect.htmlReference added —https://www.exploit-db.com/exploits/40745/Reference added —https://www.exploit-db.com/exploits/40823/Reference added —https://www.exploit-db.com/exploits/41015/Reference removed http://blog.trendmicro.com/trendlabs-security-intelligence/one-bit-rule-system-analyzing-cve-2016-7255-exploit-wild/—Reference removed http://packetstormsecurity.com/files/140468/Microsoft-Windows-Kernel-win32k.sys-NtSetWindowLongPtr-Privilege-Escalation.html—Reference removed http://www.securityfocus.com/bid/94064—Reference removed http://www.securitytracker.com/id/1037251—Reference removed https://docs.microsoft.com/en-us/security-updates/securitybulletins/2016/ms16-135—Reference removed https://github.com/mwrlabs/CVE-2016-7255—Reference removed https://securingtomorrow.mcafee.com/mcafee-labs/digging-windows-kernel-privilege-escalation-vulnerability-cve-2016-7255/—Reference removed https://security.googleblog.com/2016/10/disclosing-vulnerabilities-to-protect.html—Reference removed https://www.exploit-db.com/exploits/40745/—Reference removed https://www.exploit-db.com/exploits/40823/—Reference removed https://www.exploit-db.com/exploits/41015/—Reference type removed http://blog.trendmicro.com/trendlabs-security-intelligence/one-bit-rule-system-analyzing-cve-2016-7255-exploit-wild/ Types: Broken Link—Reference type removed http://packetstormsecurity.com/files/140468/Microsoft-Windows-Kernel-win32k.sys-NtSetWindowLongPtr-Privilege-Escalation.html Types: Exploit, Third Party Advisory, VDB Entry—Reference type removed http://www.securityfocus.com/bid/94064 Types: Broken Link, Third Party Advisory, VDB Entry—Reference type removed http://www.securitytracker.com/id/1037251 Types: Broken Link, Third Party Advisory, VDB Entry—Reference type removed https://docs.microsoft.com/en-us/security-updates/securitybulletins/2016/ms16-135 Types: Patch, Vendor Advisory—Reference type removed https://github.com/mwrlabs/CVE-2016-7255 Types: Exploit, Third Party Advisory—Reference type removed https://securingtomorrow.mcafee.com/mcafee-labs/digging-windows-kernel-privilege-escalation-vulnerability-cve-2016-7255/ Types: Broken Link—Reference type removed https://security.googleblog.com/2016/10/disclosing-vulnerabilities-to-protect.html Types: Third Party Advisory—Reference type removed https://www.exploit-db.com/exploits/40745/ Types: Exploit, Third Party Advisory, VDB Entry—Reference type removed https://www.exploit-db.com/exploits/40823/ Types: Exploit, Third Party Advisory, VDB Entry—Reference type removed https://www.exploit-db.com/exploits/41015/ Types: Exploit, Third Party Advisory, VDB Entry—Source identifier: secure@microsoft.com
Record modifiedCISA ADP
CISA assessment (SSVC): exploitation: active, automatable: no
Show 4 original changes
Individual changes of this event as published by NVD Type Action Before After Reference added —https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2016-7255Reference removed https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2016-7255—Reference type removed https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2016-7255 Types: US Government Resource—SSVC assessment changed {"id":"CVE-2016-7255","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2025-02-10T16:41:26.496082Z"}{"id":"CVE-2016-7255","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2021-03-05T00:00:00+00:00"}Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0
Record modifiedCVE Program
New references:- http://blog.trendmicro.com/trendlabs-security-intelligence/one-bit-rule-system-analyzing-cve-2016-7255-exploit-wild/
- http://packetstormsecurity.com/files/140468/Microsoft-Windows-Kernel-win32k.sys-NtSetWindowLongPtr-Privilege-Escalation.html
- http://www.securityfocus.com/bid/94064
- http://www.securitytracker.com/id/1037251
and 7 more references
Show 33 original changes
Individual changes of this event as published by NVD Type Action Before After Reference added —http://blog.trendmicro.com/trendlabs-security-intelligence/one-bit-rule-system-analyzing-cve-2016-7255-exploit-wild/Reference added —http://packetstormsecurity.com/files/140468/Microsoft-Windows-Kernel-win32k.sys-NtSetWindowLongPtr-Privilege-Escalation.htmlReference added —http://www.securityfocus.com/bid/94064Reference added —http://www.securitytracker.com/id/1037251Reference added —https://docs.microsoft.com/en-us/security-updates/securitybulletins/2016/ms16-135Reference added —https://github.com/mwrlabs/CVE-2016-7255Reference added —https://securingtomorrow.mcafee.com/mcafee-labs/digging-windows-kernel-privilege-escalation-vulnerability-cve-2016-7255/Reference added —https://security.googleblog.com/2016/10/disclosing-vulnerabilities-to-protect.htmlReference added —https://www.exploit-db.com/exploits/40745/Reference added —https://www.exploit-db.com/exploits/40823/Reference added —https://www.exploit-db.com/exploits/41015/Reference removed http://blog.trendmicro.com/trendlabs-security-intelligence/one-bit-rule-system-analyzing-cve-2016-7255-exploit-wild/—Reference removed http://packetstormsecurity.com/files/140468/Microsoft-Windows-Kernel-win32k.sys-NtSetWindowLongPtr-Privilege-Escalation.html—Reference removed http://www.securityfocus.com/bid/94064—Reference removed http://www.securitytracker.com/id/1037251—Reference removed https://docs.microsoft.com/en-us/security-updates/securitybulletins/2016/ms16-135—Reference removed https://github.com/mwrlabs/CVE-2016-7255—Reference removed https://securingtomorrow.mcafee.com/mcafee-labs/digging-windows-kernel-privilege-escalation-vulnerability-cve-2016-7255/—Reference removed https://security.googleblog.com/2016/10/disclosing-vulnerabilities-to-protect.html—Reference removed https://www.exploit-db.com/exploits/40745/—Reference removed https://www.exploit-db.com/exploits/40823/—Reference removed https://www.exploit-db.com/exploits/41015/—Reference type removed http://blog.trendmicro.com/trendlabs-security-intelligence/one-bit-rule-system-analyzing-cve-2016-7255-exploit-wild/ Types: Broken Link—Reference type removed http://packetstormsecurity.com/files/140468/Microsoft-Windows-Kernel-win32k.sys-NtSetWindowLongPtr-Privilege-Escalation.html Types: Exploit, Third Party Advisory, VDB Entry—Reference type removed http://www.securityfocus.com/bid/94064 Types: Broken Link, Third Party Advisory, VDB Entry—Reference type removed http://www.securitytracker.com/id/1037251 Types: Broken Link, Third Party Advisory, VDB Entry—Reference type removed https://docs.microsoft.com/en-us/security-updates/securitybulletins/2016/ms16-135 Types: Patch, Vendor Advisory—Reference type removed https://github.com/mwrlabs/CVE-2016-7255 Types: Exploit, Third Party Advisory—Reference type removed https://securingtomorrow.mcafee.com/mcafee-labs/digging-windows-kernel-privilege-escalation-vulnerability-cve-2016-7255/ Types: Broken Link—Reference type removed https://security.googleblog.com/2016/10/disclosing-vulnerabilities-to-protect.html Types: Third Party Advisory—Reference type removed https://www.exploit-db.com/exploits/40745/ Types: Exploit, Third Party Advisory, VDB Entry—Reference type removed https://www.exploit-db.com/exploits/40823/ Types: Exploit, Third Party Advisory, VDB Entry—Reference type removed https://www.exploit-db.com/exploits/41015/ Types: Exploit, Third Party Advisory, VDB Entry—Source identifier: af854a3a-2127-422b-91ae-364da2661108
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