CriticalCVE-2021-31199

    Microsoft Enhanced Cryptographic Provider Elevation of Privilege Vulnerability (CVE-2021-31199)

    Published In CISA KEV since Sources: CVE.org

    What is affected, what to do

    Microsoft Enhanced Cryptographic Provider Elevation of Privilege Vulnerability

    The vulnerability is being actively exploited; treat it as a priority. Update Microsoft Windows 10 Version 1809 to version 10.0.17763.1999, Microsoft Windows Server 2019 to version 10.0.17763.1999, Microsoft Windows Server 2019 (Server Core installation) to version 10.0.17763.1999. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Microsoft Windows 10 Version 1809 lt 10.0.0..10.0.17763.1999
    • Microsoft Windows Server 2019 lt 10.0.0..10.0.17763.1999
    • Microsoft Windows Server 2019 (Server Core installation) lt 10.0.0..10.0.17763.1999
    • Microsoft Windows 10 Version 1909 lt 10.0.0..10.0.18363.1621
    • Microsoft Windows 10 Version 21H1 lt 10.0.0..10.0.19043.1052
    • Microsoft Windows 10 Version 2004 lt 10.0.0..10.0.19041.1052
    • Microsoft Windows Server version 2004 lt 10.0.0..10.0.19041.1052
    • Microsoft Windows 10 Version 20H2 lt 10.0.0..10.0.19042.1052
    • Microsoft Windows Server version 20H2 lt 10.0.0..10.0.19042.1052
    • Microsoft Windows 10 Version 1507 lt 10.0.0..10.0.10240.18967
    • Microsoft Windows 10 Version 1607 lt 10.0.0..10.0.14393.4467
    • Microsoft Windows Server 2016 lt 10.0.0..10.0.14393.4467
    • Microsoft Windows Server 2016 (Server Core installation) lt 10.0.0..10.0.14393.4467
    • Microsoft Windows 7 lt 6.1.0..6.1.7601.25632
    • Microsoft Windows 7 Service Pack 1 lt 6.1.0..6.1.7601.25632
    • Microsoft Windows 8.1 lt 6.3.0..6.3.9600.20045
    • Microsoft Windows 8.1 lt 6.3.0..6.3.9600.20044
    • Microsoft Windows Server 2008 Service Pack 2 lt 6.0.0..6.0.6003.21137
    • Microsoft Windows Server 2008 Service Pack 2 (Server Core installation) lt 6.0.0..6.0.6003.21137
    • Microsoft Windows Server 2008 R2 Service Pack 1 lt 6.1.0..6.1.7601.25632
    • Microsoft Windows Server 2008 R2 Service Pack 1 (Server Core installation) lt 6.0.0..6.1.7601.25632
    • Microsoft Windows Server 2012 lt 6.2.0..6.2.9200.23372
    • Microsoft Windows Server 2012 (Server Core installation) lt 6.2.0..6.2.9200.23372
    • Microsoft Windows Server 2012 R2 lt 6.3.0..6.3.9600.20045
    • Microsoft Windows Server 2012 R2 lt 6.3.0..6.3.9600.20044
    • Microsoft Windows Server 2012 R2 (Server Core installation) lt 6.3.0..6.3.9600.20045
    • Microsoft Windows Server 2012 R2 (Server Core installation) lt 6.3.0..6.3.9600.20044
    Fixed in
    • Microsoft Windows 10 Version 1809 10.0.17763.1999
    • Microsoft Windows Server 2019 10.0.17763.1999
    • Microsoft Windows Server 2019 (Server Core installation) 10.0.17763.1999
    • Microsoft Windows 10 Version 1909 10.0.18363.1621
    • Microsoft Windows 10 Version 21H1 10.0.19043.1052
    • Microsoft Windows 10 Version 2004 10.0.19041.1052
    • Microsoft Windows Server version 2004 10.0.19041.1052
    • Microsoft Windows 10 Version 20H2 10.0.19042.1052
    • Microsoft Windows Server version 20H2 10.0.19042.1052
    • Microsoft Windows 10 Version 1507 10.0.10240.18967
    • Microsoft Windows 10 Version 1607 10.0.14393.4467
    • Microsoft Windows Server 2016 10.0.14393.4467
    • Microsoft Windows Server 2016 (Server Core installation) 10.0.14393.4467
    • Microsoft Windows 7 6.1.7601.25632
    • Microsoft Windows 7 Service Pack 1 6.1.7601.25632
    • Microsoft Windows 8.1 6.3.9600.20045
    • Microsoft Windows 8.1 6.3.9600.20044
    • Microsoft Windows Server 2008 Service Pack 2 6.0.6003.21137
    • Microsoft Windows Server 2008 Service Pack 2 (Server Core installation) 6.0.6003.21137
    • Microsoft Windows Server 2008 R2 Service Pack 1 6.1.7601.25632
    • Microsoft Windows Server 2008 R2 Service Pack 1 (Server Core installation) 6.1.7601.25632
    • Microsoft Windows Server 2012 6.2.9200.23372
    • Microsoft Windows Server 2012 (Server Core installation) 6.2.9200.23372
    • Microsoft Windows Server 2012 R2 6.3.9600.20045
    • Microsoft Windows Server 2012 R2 6.3.9600.20044
    • Microsoft Windows Server 2012 R2 (Server Core installation) 6.3.9600.20045
    • Microsoft Windows Server 2012 R2 (Server Core installation) 6.3.9600.20044

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    5.2

    Priority

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

    Source: NVD, CVSS v3

    5.2

    CVSS v3

    Severity Medium on the scale from 0 to 10.

    Source: CVE.org

    2.9 %

    EPSS score

    Moderate — model estimates 1-10% exploitation likelihood.

    Source: FIRST EPSS, percentile 87.1

    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
    186.73 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: ANSSI / CERT-FR 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
    5.2 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
    5.2
    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
    2.9 %
    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
    87.1
    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 20 March 2024

    Response and mitigation

    Why act now?

    Prioritisation rationale

    The flaw requires local access with low privileges, which keeps its base severity moderate, but the scope change lets an attacker break out of a sandboxed or user context — making it a favoured second link in exploit chains that start with document or browser code execution. Exploitation likelihood is comparatively high for a local privilege escalation, and CISA does not flag known ransomware use. Typical targets are standard office workstations handling email and PDFs, plus neglected legacy systems. Because the fix has been available since June 2021, treat any remaining vulnerable host as a high-priority finding — less for the bug itself than for the patch-management failure it exposes, which is directly relevant to NIS2 Article 21 vulnerability-handling obligations.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Verify patch level and deploy the June 2021 security update (or any later cumulative update). Minimum fixed builds per the advisory: Windows 10 1507 → 10.0.10240.18967, 1607 → 10.0.14393.4467, 1809 → 10.0.17763.1999, 1909 → 10.0.18363.1621, 2004/20H2/21H1 → 10.0.19041/19042/19043.1052, Windows 7 SP1 → 6.1.7601.25632 (ESU required). Look up the KB number per build in the Microsoft Security Update Guide; check server editions sharing the same codebase in the advisory as well.
      • Inventory vulnerable hosts: reg query "HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion" /v UBR, or in Defender: DeviceTvmSoftwareVulnerabilities | where CveId == "CVE-2021-31199". Any hit today points to a broader patch-management gap.
      • Move unsupported Windows 7 / Windows 10 builds with no update path (OT HMIs, lab machines) into an isolated segment and block interactive logons by standard users.
      • Triage endpoints showing suspicious process chains (see detection rules): this flaw in rsaenh.dll is typically used as a second stage after initial code execution via weaponised documents or PDFs.
      • If compromise is suspected: isolate the host via EDR, rotate local admin and cached domain credentials (reset the LAPS password), capture a memory image.

    2. Runbook step 2

      Mitigation layers

      • Endpoint hardening (cut the initial vector): enable Microsoft Defender ASR rules in block mode — "Block all Office applications from creating child processes" (D4F940AB-401B-4EFC-AADC-AD5F3C50688A) and "Block Adobe Reader from creating child processes" (7674BA52-37EB-4A4F-A9A1-F0F9A1619A2C). Run PDF readers only with Protected Mode/sandbox enabled.
      • Application control: WDAC or AppLocker allowlisting that denies execution from user-writable paths (%APPDATA%, %TEMP%, Downloads) to stop exploit payload staging.
      • IAM / least privilege: remove local admin rights, enforce LAPS/Windows LAPS, enable Credential Guard and LSA protection (RunAsPPL=1) to limit the payoff of a successful escalation (LSASS credential dumping).
      • Network segmentation (post-escalation containment): block workstation-to-workstation SMB (445/tcp), RPC (135/tcp) and WinRM (5985/5986/tcp) via host firewall GPO to slow lateral movement once SYSTEM is obtained.
      • Mail/web gateway: detonate or quarantine external macro-enabled Office files and PDFs; ensure Mark-of-the-Web is enforced.

    3. Runbook step 3

      Detection rules

      • Integrity-level jump (EDR/MDE): DeviceProcessEvents | where InitiatingProcessIntegrityLevel in ("Low","Medium") and ProcessIntegrityLevel == "System" and InitiatingProcessFileName !in~ ("services.exe","svchost.exe","msiexec.exe") — a standard-user process spawning a SYSTEM child.
      • Sysmon EID 1 / Windows EID 4688: cmd.exe, powershell.exe or rundll32.exe under WINWORD.EXE, EXCEL.EXE, AcroRd32.exe or Acrobat.exe, especially running as NT AUTHORITY\SYSTEM. Sigma shape: ParentImage|endswith: ['\AcroRd32.exe','\WINWORD.EXE'] AND User|contains: 'SYSTEM'.
      • Windows EID 4672 / 4624: special privileges (SeDebugPrivilege, SeImpersonatePrivilege) assigned shortly after a standard user opens a document; correlate with EID 4688 on the same host.
      • Post-escalation activity: Sysmon EID 10 with TargetImage = lsass.exe and GrantedAccess 0x1010/0x1410 from unusual processes; EID 7045/4697 (new service) shortly after document open.
      • Sysmon EID 7 (supplementary, noisy): rsaenh.dll loaded by processes running from %TEMP%/%APPDATA% — use only as context alongside the rules 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

    Microsoft Enhanced Cryptographic Provider Elevation of Privilege Vulnerability

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

    Vendors and products

    Affected operating systems

    Affected operating systems
    WindowsMicrosoftWindows 10 Version 150710.0.10240.18967
    WindowsMicrosoftWindows 10 Version 160710.0.14393.4467
    WindowsMicrosoftWindows 10 Version 180910.0.17763.1999
    WindowsMicrosoftWindows 10 Version 190910.0.18363.1621
    WindowsMicrosoftWindows 10 Version 200410.0.19041.1052
    WindowsMicrosoftWindows 10 Version 20H210.0.19042.1052
    WindowsMicrosoftWindows 10 Version 21H110.0.19043.1052
    WindowsMicrosoftWindows 76.1.7601.25632
    WindowsMicrosoftWindows 7 Service Pack 16.1.7601.25632
    WindowsMicrosoftWindows 8.16.3.9600.20045
    WindowsMicrosoftWindows Server 2008 R2 Service Pack 16.1.7601.25632
    WindowsMicrosoftWindows Server 2008 R2 Service Pack 1 (Server Core installation)6.1.7601.25632
    WindowsMicrosoftWindows Server 2008 Service Pack 26.0.6003.21137
    WindowsMicrosoftWindows Server 2008 Service Pack 2 (Server Core installation)6.0.6003.21137
    WindowsMicrosoftWindows Server 20126.2.9200.23372
    WindowsMicrosoftWindows Server 2012 (Server Core installation)6.2.9200.23372
    WindowsMicrosoftWindows Server 2012 R26.3.9600.20045
    WindowsMicrosoftWindows Server 2012 R2 (Server Core installation)6.3.9600.20045
    WindowsMicrosoftWindows Server 201610.0.14393.4467
    WindowsMicrosoftWindows Server 2016 (Server Core installation)10.0.14393.4467
    WindowsMicrosoftWindows Server 201910.0.17763.1999
    WindowsMicrosoftWindows Server 2019 (Server Core installation)10.0.17763.1999
    WindowsMicrosoftWindows Server version 200410.0.19041.1052
    WindowsMicrosoftWindows Server version 20H210.0.19042.1052

    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 CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited
    ANSSI / CERT-FRLicence Ouverte 2.0, as of CERTFR-2021-ALE-012 – Multiples vulnérabilités dans Microsoft Windows (clôturée 2021-10-19) (opens in a new tab)cert.cyber.gouv.fractively exploited

    References & sources

    • portal.msrc.microsoft.comen-US/security-guidance/advisory/CVE-2021-31199x_refsource_MISC, Patch, Vendor advisory
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2021-31199government-resource, US government resource
    • cert.cyber.gouv.frANSSI / CERT-FR: CERTFR-2021-ALE-012 – Multiples vulnérabilités dans Microsoft Windows (clôturée 2021-10-19)cert-fr
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    <a href="https://intel.neosec.eu/en/cve/CVE-2021-31199"><img src="https://intel.neosec.eu/badge/cve/CVE-2021-31199.svg?lang=en" alt="CVE-2021-31199 – NEOSEC Intel" height="20"></a>