CriticalCVE-2026-21525

Windows Remote Access Connection Manager Denial of Service Vulnerability (CVE-2026-21525)

Published 10.02.2026In CISA KEV since 10.02.2026Sources: pwn.watch, CVE.org, Msrc Update Guide, EUVD

What is affected, what to do

Null pointer dereference in Windows Remote Access Connection Manager allows an unauthorized attacker to deny service locally.

The vulnerability is being actively exploited; treat it as a priority. Update Microsoft Windows 10 Version 1607 to version 10.0.14393.8868, Microsoft Windows 10 Version 1809 to version 10.0.17763.8389, Microsoft Windows 10 Version 21H2 to version 10.0.19044.6937. Immediate actions, mitigation and detection rules are in the runbook below.

Affected: Microsoft Windows 10 Version 1607 lt 10.0.14393.0..10.0.14393.8868
Microsoft Windows 10 Version 1809 lt 10.0.17763.0..10.0.17763.8389
Microsoft Windows 10 Version 21H2 lt 10.0.19044.0..10.0.19044.6937
Microsoft Windows 10 Version 22H2 lt 10.0.19045.0..10.0.19045.6937
Microsoft Windows 11 version 22H3 lt 10.0.22631.0..10.0.22631.6649
Microsoft Windows 11 Version 23H2 lt 10.0.22631.0..10.0.22631.6649
Microsoft Windows 11 Version 24H2 lt 10.0.26100.0..10.0.26100.7840
Microsoft Windows 11 Version 25H2 lt 10.0.26200.0..10.0.26200.7840
Microsoft Windows 11 version 26H1 lt 10.0.28000.0..10.0.28000.1575
Microsoft Windows Server 2012 lt 6.2.9200.0..6.2.9200.25923
Microsoft Windows Server 2012 (Server Core installation) lt 6.2.9200.0..6.2.9200.25923
Microsoft Windows Server 2012 R2 lt 6.3.9600.0..6.3.9600.23022
Microsoft Windows Server 2012 R2 (Server Core installation) lt 6.3.9600.0..6.3.9600.23022
Microsoft Windows Server 2016 lt 10.0.14393.0..10.0.14393.8868
Microsoft Windows Server 2016 (Server Core installation) lt 10.0.14393.0..10.0.14393.8868
Microsoft Windows Server 2019 lt 10.0.17763.0..10.0.17763.8389
Microsoft Windows Server 2019 (Server Core installation) lt 10.0.17763.0..10.0.17763.8389
Microsoft Windows Server 2022 lt 10.0.20348.0..10.0.20348.4773
Microsoft Windows Server 2022, 23H2 Edition (Server Core installation) lt 10.0.25398.0..10.0.25398.2149
Microsoft Windows Server 2025 lt 10.0.26100.0..10.0.26100.32370
Microsoft Windows Server 2025 (Server Core installation) lt 10.0.26100.0..10.0.26100.32370
Fixed in: Microsoft Windows 10 Version 1607 10.0.14393.8868
Microsoft Windows 10 Version 1809 10.0.17763.8389
Microsoft Windows 10 Version 21H2 10.0.19044.6937
Microsoft Windows 10 Version 22H2 10.0.19045.6937
Microsoft Windows 11 version 22H3 10.0.22631.6649
Microsoft Windows 11 Version 23H2 10.0.22631.6649
Microsoft Windows 11 Version 24H2 10.0.26100.7840
Microsoft Windows 11 Version 25H2 10.0.26200.7840
Microsoft Windows 11 version 26H1 10.0.28000.1575
Microsoft Windows Server 2012 6.2.9200.25923
Microsoft Windows Server 2012 (Server Core installation) 6.2.9200.25923
Microsoft Windows Server 2012 R2 6.3.9600.23022
Microsoft Windows Server 2012 R2 (Server Core installation) 6.3.9600.23022
Microsoft Windows Server 2016 10.0.14393.8868
Microsoft Windows Server 2016 (Server Core installation) 10.0.14393.8868
Microsoft Windows Server 2019 10.0.17763.8389
Microsoft Windows Server 2019 (Server Core installation) 10.0.17763.8389
Microsoft Windows Server 2022 10.0.20348.4773
Microsoft Windows Server 2022, 23H2 Edition (Server Core installation) 10.0.25398.2149
Microsoft Windows Server 2025 10.0.26100.32370
Microsoft Windows Server 2025 (Server Core installation) 10.0.26100.32370

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Metrics

6.2

Priority

XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

Source: NVD, CVSS v3

6.2

CVSS v3

Severity Medium on the scale from 0 to 10.

Source: pwn.watch, CVE.org, Msrc Update Guide, EUVD

4.9 %

EPSS score

Moderate — model estimates 1-10% exploitation likelihood.

Source: FIRST EPSS, percentile 92.0

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: 212.94 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 exploitedSource: VulnCheck KEV (opens in a new tab) How we classify
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: 6.2 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: 6.2
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: 4.9 %; Moderate — model estimates 1-10% 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: 92.0; 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: 10.02.2026
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: 10.02.2026
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-476

Response and mitigation

Why act now?

Prioritisation rationale

This flaw only allows a local denial of service against a SYSTEM service, with no impact on confidentiality or integrity. However, once code runs locally, it needs no privileges and no user interaction. Its KEV listing, combined with an exploitation likelihood that is unusually high for a local DoS bug, suggests attackers use it for disruption or as a stepping stone in exploit chains. CISA does not flag it for known ransomware use. For most organisations this belongs in an accelerated regular patch cycle, meaning the next maintenance window. Escalate it where many users share local access (terminal servers, VDI) or where VPN availability is business-critical, such as KRITIS remote-maintenance access.

01
Runbook step 1
Immediate response (0-24 h)
- Deploy the Windows cumulative security update that brings hosts to at least these builds: Windows 10 1607 → 10.0.14393.8868, 1809 → 10.0.17763.8389, 21H2 → 10.0.19044.6937, 22H2 → 10.0.19045.6937, Windows 11 22H3/23H2 → 10.0.22631.6649, 24H2 → 10.0.26100.7840, 25H2 → 10.0.26200.7840. The patch is available from Microsoft — look up the KB number in the Microsoft Security Update Guide.
- Verify patch level from inventory (build plus UBR): Get-ItemProperty 'HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion' | Select CurrentBuild, UBR. Flag anything below the listed builds as vulnerable.
- Patch multi-user and VPN-dependent systems first: terminal servers/VDI hosts, jump hosts, and clients relying on Always On VPN or the built-in Windows VPN client. On these systems a RasMan crash drops remote-access sessions.
- Check whether the RasMan service (Remote Access Connection Manager) has terminated unexpectedly since 2026-02-10 (System log, Event ID 7031/7034). Treat any hit as a possible exploitation attempt and identify the local process and user that triggered it.
- For vulnerable hosts without a near-term patch window, record a time-boxed risk acceptance (NIS2 evidence) and enable the compensating controls below.
02
Runbook step 2
Mitigation layers
- Configuration/service hardening: On systems with no VPN, dial-up or RAS use, disable RasMan (Set-Service RasMan -StartupType Disabled). First check for dependencies such as VPN clients, mobile broadband or third-party software, and pilot the change on a test group.
- Availability: Configure service recovery to restart automatically, so a crash only interrupts VPN connectivity briefly: sc.exe failure RasMan reset= 86400 actions= restart/60000/restart/60000/restart/60000. This limits impact; it does not close the vulnerability.
- IAM/least privilege: Exploitation requires local code execution. Tighten interactive and RDP logon rights on servers and jump hosts via GPO ("Allow log on locally" / "Allow log on through Remote Desktop Services") and eliminate shared accounts.
- Endpoint hardening: Use WDAC or AppLocker to block unapproved binaries and scripts in user-writable paths (%TEMP%, %APPDATA%, Downloads). This makes it harder to drop a trigger tool.
- Network: There is no direct network rule for this flaw, because the attack vector is local. Reduce initial-access opportunities instead: MFA on the VPN gateway, macro and attachment controls, and segmentation of terminal-server farms.
03
Runbook step 3
Detection rules
- Windows System log: Service Control Manager Event ID 7031/7034 for "Remote Access Connection Manager". Example KQL: Event | where Source == "Service Control Manager" and EventID in (7031,7034) and RenderedDescription has "Remote Access Connection Manager". Repeated crashes on one host within a short window are a strong signal.
- Windows Application log: Event ID 1000 (Application Error) or 1001 (WER) with faulting process svchost.exe and faulting module rasmans.dll. Example SPL: index=wineventlog EventCode=1000 Message="*rasmans.dll*".
- EDR/Sysmon: Correlate Sysmon EID 1 process creations by non-admin users from user-writable paths within ±2 min before the RasMan crash. The goal is to find the process chain that triggered the crash.
- Follow-on activity: A crashed SYSTEM service can be one link in an exploit chain. After a crash, review the same host for new service installs (System 7045, Security 4697), token manipulation, or new SYSTEM processes with an unexpected parent.
- Operational telemetry: Correlate spikes in VPN disconnects (RasClient events in the Application log, VPN gateway logs) that have no network-side cause with the crash events above.

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

Null pointer dereference in Windows Remote Access Connection Manager allows an unauthorized attacker to deny service locally.

Source: pwn.watch, NVD (NIST), Microsoft Security Update Guide, cvelistv5, CISA KEV Catalog, ENISA EUVD, CVE.org (MITRE)

Affected products

The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

Affected products
		Affected versions	Fixed in
Microsoft	Windows 10 Version 1607	`10.0.14393.0 – < 10.0.14393.8868`	`10.0.14393.8868`
Microsoft	Windows 10 Version 1809	`10.0.17763.0 – < 10.0.17763.8389`	`10.0.17763.8389`
Microsoft	Windows 10 Version 21H2	`10.0.19044.0 – < 10.0.19044.6937`	`10.0.19044.6937`
Microsoft	Windows 10 Version 22H2	`10.0.19045.0 – < 10.0.19045.6937`	`10.0.19045.6937`
Microsoft	Windows 11 version 22H3	`10.0.22631.0 – < 10.0.22631.6649`	`10.0.22631.6649`
Microsoft	Windows 11 Version 23H2	`10.0.22631.0 – < 10.0.22631.6649`	`10.0.22631.6649`
Microsoft	Windows 11 Version 24H2	`10.0.26100.0 – < 10.0.26100.7840`	`10.0.26100.7840`
Microsoft	Windows 11 Version 25H2	`10.0.26200.0 – < 10.0.26200.7840`	`10.0.26200.7840`
Microsoft	Windows 11 version 26H1	`10.0.28000.0 – < 10.0.28000.1575`	`10.0.28000.1575`
Microsoft	Windows Server 2012	`6.2.9200.0 – < 6.2.9200.25923`	`6.2.9200.25923`
Microsoft	Windows Server 2012 (Server Core installation)	`6.2.9200.0 – < 6.2.9200.25923`	`6.2.9200.25923`
Microsoft	Windows Server 2012 R2	`6.3.9600.0 – < 6.3.9600.23022`	`6.3.9600.23022`
Microsoft	Windows Server 2012 R2 (Server Core installation)	`6.3.9600.0 – < 6.3.9600.23022`	`6.3.9600.23022`
Microsoft	Windows Server 2016	`10.0.14393.0 – < 10.0.14393.8868`	`10.0.14393.8868`
Microsoft	Windows Server 2016 (Server Core installation)	`10.0.14393.0 – < 10.0.14393.8868`	`10.0.14393.8868`
Microsoft	Windows Server 2019	`10.0.17763.0 – < 10.0.17763.8389`	`10.0.17763.8389`
Microsoft	Windows Server 2019 (Server Core installation)	`10.0.17763.0 – < 10.0.17763.8389`	`10.0.17763.8389`
Microsoft	Windows Server 2022	`10.0.20348.0 – < 10.0.20348.4773`	`10.0.20348.4773`
Microsoft	Windows Server 2022, 23H2 Edition (Server Core installation)	`10.0.25398.0 – < 10.0.25398.2149`	`10.0.25398.2149`
Microsoft	Windows Server 2025	`10.0.26100.0 – < 10.0.26100.32370`	`10.0.26100.32370`
Microsoft	Windows Server 2025 (Server Core installation)	`10.0.26100.0 – < 10.0.26100.32370`	`10.0.26100.32370`

Vendors and products

Affected operating systems

Affected operating systems

Windows	microsoft	windows_10_1607	—
Windows	microsoft	windows_10_1809	—
Windows	microsoft	windows_10_21h2	—
Windows	microsoft	windows_10_22h2	—
Windows	microsoft	windows_11_23h2	—
Windows	microsoft	windows_11_24h2	—
Windows	microsoft	windows_11_25h2	—
Windows	microsoft	windows_server_2012	`r2`
Windows	microsoft	windows_server_2012	—
Windows	microsoft	windows_server_2016	—
Windows	microsoft	windows_server_2019	—
Windows	microsoft	windows_server_2022	—
Windows	microsoft	windows_server_2022_23h2	—
Windows	microsoft	windows_server_2025	—

Weakness classes (CWE)

CWE-476NULL Pointer Dereference
Base
The product dereferences a pointer that it expects to be valid but is NULL.
Entry at MITRE CWE-476

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.

Public exploit references

CISA KEV Catalog	CISA Known Exploited Vulnerability (opens in a new tab)cisa.gov	actively exploited	10.02.2026

References & sources

Microsoft Security Update GuideWindows Remote Access Connection Manager Denial of Service Vulnerabilityeuvd, Vendor advisory, Patch, Vendor advisory, pwn-watch
cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2026-21525government-resource, US government resource
vicarius.iovsociety/posts/cve-2026-21525-detection-script-dos-vulnerabilit…Third-party advisory
vicarius.iovsociety/posts/cve-2026-21525-mitigation-script-dos-vulnerabili…Mitigation, Third-party advisory
pwn.watchpwn.watch: Microsoft Windows: Microsoft MSHTML Framework Protection Mechanism Failure Vulnerabilitypwn-watch
Microsoft Security Update GuideMicrosoft Windows — CVE-2026-21513pwn-watch
NVD (NIST)NVD: CVE-2026-21513pwn-watch
NVD (NIST)NVD: CVE-2026-21525pwn-watch
Microsoft Security Update GuideMicrosoft Windows — CVE-2026-21510pwn-watch
NVD (NIST)NVD: CVE-2026-21510pwn-watch

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<a href="https://intel.neosec.eu/en/cve/CVE-2026-21525"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-21525.svg?lang=en" alt="CVE-2026-21525 – NEOSEC Intel" height="20"></a>

What is affected, what to do

Metrics

Response and mitigation

Prioritisation rationale

Immediate response (0-24 h)

Mitigation layers

Detection rules

Detection rules

Classification under NIS2 and CRA

Description

Affected products

Vendors and products

Affected operating systems

Weakness classes (CWE)

Public exploit references

References & sources