Microsoft Windows Secondary Logon Service Privilege Escalation Vulnerability (CVE-2016-0099)
Published In CISA KEV since Sources: CVE.org
What is affected, what to do
The Secondary Logon Service 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, and Windows 10 Gold and 1511 does not properly process request handles, which allows local users to gain privileges via a crafted application, aka "Secondary Logon 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
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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
37.1 %
EPSS score
Elevated — model estimates 10-50% exploitation likelihood.
Source: FIRST EPSS, percentile 98.5
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- 241.63 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- 37.1 %
- 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- 98.5
- 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 10 February 2025
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-120
Response and mitigation
Why act now?
Prioritisation rationale
This CVE is on the CISA KEV list and flagged as used in ransomware campaigns — it is a long-standing staple of post-compromise toolkits (bundled into Mimikatz workflows and commodity LPE suites). The vector is local, so an initial-access payload (phishing, drive-by, trojanised software) is required first; once that foothold exists, exploitation likelihood is very high and public exploit code has been readily available for years. Rate this critical for multi-user systems (RDS/Citrix/VDI), developer workstations with elevated attack surface, and legacy servers lacking a regular patch cadence; with a correctly tiered admin model and MS16-032 universally deployed, residual risk drops to acceptable. The realistic worst case is unpatched endpoints combined with a flat AD tiering, which turns a single phished workstation into a direct path to Domain Admin.
Runbook step 1
Immediate response (0-24 h)
- Deploy Microsoft Security Bulletin MS16-032 (KB3139914) across all affected systems: Windows Vista SP2, Server 2008 SP2 / R2 SP1, Windows 7 SP1, 8.1, RT 8.1, Server 2012 Gold/R2, Windows 10 Gold and 1511. Prioritise multi-user systems (Terminal/RDS servers, Citrix farms, jump hosts, build agents).
- Identify legacy systems with no feasible patch window — notably Server 2008 R2 and Windows 7 without an active ESU contract — and move them into a segmented VLAN with strict egress filtering.
- On hosts that cannot be patched immediately, inspect the Secondary Logon service (seclogon): if RunAs / "Run as different user" is not an operational requirement, disable it (
sc config seclogon start= disabled+sc stop seclogon). - Inventory local administrator rights on endpoints and servers; revoke interactive logon rights for standard user accounts on servers (local presence is required to exploit this LPE).
- Rotate credentials and Kerberos tickets (double-rotate krbtgt where compromise is suspected) on any host flagged as potentially touched; reseed local-admin passwords via LAPS.
- Obtain CAB freeze exception for MS16-032 and roll it out via WSUS/SCCM/Intune as "Critical", enforcing a reboot window within 72 hours.
Runbook step 2
Mitigation layers
- Network segmentation: restrict interactive logons (RDP/WinRM) to unpatched hosts so they only accept connections from PAW jump hosts; block workstation-to-workstation SMB/RDP via host firewall to contain lateral movement that precedes the LPE.
- Endpoint hardening: enforce AppLocker / WDAC in "Enforce" mode for
%TEMP%,%APPDATA%,C:\Users\Public— the usual drop zones for LPE exploit binaries. Push PowerShell Constrained Language Mode and lock down common LOLBAS (mshta.exe, rundll32.exe) on user workstations. - IAM / least privilege: apply Microsoft Enterprise Access Model tiering; Domain Admins must not log on to Tier-2 workstations. Enable the Protected Users group for privileged accounts.
- Configuration hardening: disable the
seclogonservice enterprise-wide via GPO ("Computer Configuration → Preferences → Services") where RunAs is not needed. Raise UAC to "Always notify" (level 4). - Update EDR/AV signatures: Microsoft Defender detects known POCs as
Exploit:Win32/CVE-2016-0099; verify Cloud Protection and Tamper Protection are enabled. - Monitor for unexpected
svchost.exechild processes elevated to a SYSTEM token when the originating user context was unprivileged.
Runbook step 3
Detection rules
- Sysmon EID 1 (Process Create): processes with
ParentImage=\svchost.exeandCommandLinecontaining-k netsvcsspawning a child atIntegrityLevel=Systemwhose user SID was non-privileged beforehand. Sigma shape:parent_image|endswith: \svchost.exe+User|startswith: S-1-5-21+IntegrityLevel: System. - Windows Security EID 4672 (Special Privileges assigned) for accounts that normally hold no administrative rights; correlate with a preceding EID 4624 Type 2/10 for the same user.
- Service Control events EID 7036 / 7045 on
seclogonoutside planned maintenance — in particular service restart after crash (EID 7031). - EDR process tree:
cmd.exeorpowershell.exespawned as child of a SYSTEM process while the originating user context was non-SYSTEM — the canonical post-exploitation signature. KQL (Defender XDR):DeviceProcessEvents | where InitiatingProcessAccountName != AccountName and AccountName == "SYSTEM" and InitiatingProcessAccountName !in ("system","local service","network service"). - File-system monitoring (Sysmon EID 11) for executable drops into
C:\Windows\Tempor%LOCALAPPDATA%\Tempfollowed by execution within seconds. - Suricata/Zeek: unusual SMB admin-share access (ADMIN$, C$) immediately after a local logon event — a signal of post-LPE lateral movement.
- Sysmon EID 1 (Process Create): processes with
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 Secondary Logon Service 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, and Windows 10 Gold and 1511 does not properly process request handles, which allows local users to gain privileges via a crafted application, aka "Secondary Logon Elevation of Privilege Vulnerability."
Source: NVD (NIST), cvelistv5, CISA KEV Catalog, CVE.org (MITRE)
Vendors and products
Affected operating systems
| Windows | microsoft | windows_10_1507 | — |
| Windows | microsoft | windows_10_1511 | — |
| Windows | microsoft | windows_7 | — |
| Windows | microsoft | windows_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-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
Base
The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer.
Entry at MITRE CWE-120
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 | |
| Exploit-DB | EDB-ID 39574 (opens in a new tab)exploit-db.com | PoC (publicly reported)reported, not verified | — |
| Exploit-DB | EDB-ID 39719 (opens in a new tab)exploit-db.com | PoC (publicly reported)reported, not verified | — |
| Exploit-DB | EDB-ID 39809 (opens in a new tab)exploit-db.com | PoC (publicly reported)reported, not verified | — |
| Exploit-DB | EDB-ID 40107 (opens in a new tab)exploit-db.com | PoC (publicly reported)reported, not verified | — |
References & sources
- exploit-db.com40107Exploit, x_refsource_EXPLOIT-DB, Exploit, Third-party advisory, Vulnerability database
- exploit-db.com39719Exploit, x_refsource_EXPLOIT-DB, Exploit, Third-party advisory, Vulnerability database
- exploit-db.com39809Exploit, x_refsource_EXPLOIT-DB, Exploit, Third-party advisory, Vulnerability database
- securityfocus.com84034Vulnerability database, x_refsource_BID, Broken link, Third-party advisory, Vulnerability database
- securitytracker.com1035210Vulnerability database, x_refsource_SECTRACK, Broken link, Third-party advisory, Vulnerability database
- docs.microsoft.comMS16-032Vendor advisory, x_refsource_MS, Patch, Vendor advisory
- exploit-db.com39574Exploit, x_refsource_EXPLOIT-DB, Exploit, Third-party advisory, Vulnerability database
- cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2016-0099government-resource, US government resource
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<a href="https://intel.neosec.eu/en/cve/CVE-2016-0099"><img src="https://intel.neosec.eu/badge/cve/CVE-2016-0099.svg?lang=en" alt="CVE-2016-0099 – NEOSEC Intel" height="20"></a>