CriticalCVE-2021-36942

    Windows LSA Spoofing Vulnerability (CVE-2021-36942)

    Published Last modified In CISA KEV since Sources: CVE.org

    What is affected, what to do

    Windows LSA Spoofing Vulnerability

    The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. Update Microsoft Windows Server 2008 R2 Service Pack 1 to version 6.1.7601.25685, Microsoft Windows Server 2008 R2 Service Pack 1 (Server Core installation) to version 6.1.7601.25685, Microsoft Windows Server 2008 Service Pack 2 to version 6.0.6003.21192. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Microsoft Windows Server 2008 R2 Service Pack 1 lt 6.1.7601.0..6.1.7601.25685
    • Microsoft Windows Server 2008 R2 Service Pack 1 (Server Core installation) lt 6.1.7601.0..6.1.7601.25685
    • Microsoft Windows Server 2008 Service Pack 2 lt 6.0.6003.0..6.0.6003.21192
    • Microsoft Windows Server 2008 Service Pack 2 (Server Core installation) lt 6.0.6003.0..6.0.6003.21192
    • Microsoft Windows Server 2012 lt 6.2.9200.0..6.2.9200.23435
    • Microsoft Windows Server 2012 (Server Core installation) lt 6.2.9200.0..6.2.9200.23435
    • Microsoft Windows Server 2012 R2 lt 6.3.9600.0..6.3.9600.20094
    • Microsoft Windows Server 2012 R2 (Server Core installation) lt 6.3.9600.0..6.3.9600.20094
    • Microsoft Windows Server 2016 lt 10.0.14393.0..10.0.14393.4583
    • Microsoft Windows Server 2016 (Server Core installation) lt 10.0.14393.0..10.0.14393.4583
    • Microsoft Windows Server 2019 lt 10.0.17763.0..10.0.17763.2114
    • Microsoft Windows Server 2019 (Server Core installation) lt 10.0.17763.0..10.0.17763.2114
    • Microsoft Windows Server version 2004 lt 10.0.0..10.0.19041.1165
    • Microsoft Windows Server version 20H2 lt 10.0.0..10.0.19042.1165
    Fixed in
    • Microsoft Windows Server 2008 R2 Service Pack 1 6.1.7601.25685
    • Microsoft Windows Server 2008 R2 Service Pack 1 (Server Core installation) 6.1.7601.25685
    • Microsoft Windows Server 2008 Service Pack 2 6.0.6003.21192
    • Microsoft Windows Server 2008 Service Pack 2 (Server Core installation) 6.0.6003.21192
    • Microsoft Windows Server 2012 6.2.9200.23435
    • Microsoft Windows Server 2012 (Server Core installation) 6.2.9200.23435
    • Microsoft Windows Server 2012 R2 6.3.9600.20094
    • Microsoft Windows Server 2012 R2 (Server Core installation) 6.3.9600.20094
    • Microsoft Windows Server 2016 10.0.14393.4583
    • Microsoft Windows Server 2016 (Server Core installation) 10.0.14393.4583
    • Microsoft Windows Server 2019 10.0.17763.2114
    • Microsoft Windows Server 2019 (Server Core installation) 10.0.17763.2114
    • Microsoft Windows Server version 2004 10.0.19041.1165
    • Microsoft Windows Server version 20H2 10.0.19042.1165

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

    Metrics

    7.5

    Priority

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

    Source: NVD, CVSS v3

    7.5

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: CVE.org

    66.0 %

    EPSS score

    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.

    Source: FIRST EPSS, percentile 99.27

    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
    241.34 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
    7.5 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
    7.5
    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
    66.0 %
    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
    99.27
    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 · automatable · Technical impact: total
    Source: CISA Vulnrichment, as of 4 February 2025

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This CVE is on CISA KEV and flagged for ransomware campaign use — relevant because "PetitPotam" is the ignition step of a full domain takeover chain (coercion → NTLM relay → AD CS ESC8 → Domain Admin certificate → DCSync). The vector is network-reachable without authentication and aims straight at Domain Controllers; exploitation likelihood is among the highest observed, and public PoCs (PetitPotam.py, Impacket ntlmrelayx) have been standard red-team and ransomware tooling for years. Any organisation running Active Directory with an Enterprise CA — typical for mid-market and KRITIS environments — should treat this as P1, even though the raw CVSS vector shows only C:H/I:N/A:N: the real-world chain ends in Tier-0 compromise.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Deploy the Microsoft August/September 2021 security updates (KB5005033, KB5005565 and the matching monthly rollups for Server 2008/2008 R2/2012/2012 R2/2016/2019/20H2). Patch all Domain Controllers and AD CS / ADFS servers first, then member servers.
      • Enable Extended Protection for Authentication (EPA) on every HTTP-based AD CS role (Web Enrollment, CES, NDES) and switch IIS auth to "Require SSL" plus "Negotiate:Kerberos" — this is the most direct break of the known PetitPotam → AD CS ESC8 relay chain.
      • Close NTLM relay paths: enforce SMB signing via GPO ("Microsoft network server/client: Digitally sign communications (always) = Enabled") and configure LDAP signing plus LDAP Channel Binding on DCs (RequireSecureLDAP = 2, LdapEnforceChannelBinding = 2).
      • If full patching is not immediately possible, restrict inbound access to the MS-EFSRPC named pipes (\pipe\lsarpc, \pipe\efsrpc, \pipe\lsass, \pipe\samr) on DCs via Windows Firewall or network firewall so only dedicated admin jumphosts can reach them.
      • Audit NTLM usage and disable it where feasible: GPO "Network security: Restrict NTLM: Incoming NTLM traffic = Deny all accounts" on AD CS and other sensitive servers; baseline first with "Audit all" to avoid breaking production dependencies.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: cut SMB (445/tcp) and RPC (135/tcp plus dynamic high ports) between client VLANs and server/DC VLANs down to what is strictly required; inbound SMB to DCs only from admin networks.
      • Harden AD CS per Microsoft ADV210003 / KB5005413: disable Web Enrollment if not needed; expose EnrollmentServer endpoints only via HTTPS with EPA; review templates with "Enrollee supplies subject" (ESC1) and "Any Purpose / Client Auth" EKUs for over-broad enrollment rights.
      • SMB server on DCs: disable guest fallback and SMBv1 (Set-SmbServerConfiguration -EnableSMB1Protocol $false); set RestrictReceivingNTLMTraffic.
      • Endpoint hardening: place privileged accounts into the Protected Users group (which blocks NTLM for them); deploy LAPS on every member server to limit lateral movement value of stolen local hashes.
      • IPS/IDS: enable PetitPotam signatures (Suricata/Snort rules referencing EfsRpcOpenFileRaw, EfsRpcEncryptFileSrv, EfsRpcQueryUsersOnFile over \PIPE\lsarpc or \PIPE\efsrpc).
      • Monitor AD CS enrollment servers (IIS logs for CertSrv/CES endpoints) for anomalous NTLM authentications from machine accounts, especially DC$ accounts.

    3. Runbook step 3

      Detection rules

      • Windows Security Event 4624 Logon Type 3 on AD CS servers where AccountName ends with "$" (machine account, especially a DC) and AuthenticationPackageName = "NTLM" — textbook sign of a successful relay. KQL sketch: SecurityEvent | where EventID == 4624 and LogonType == 3 and AuthenticationPackageName == "NTLM" and TargetUserName endswith "$".
      • Zeek/Suricata telemetry for DCE/RPC calls to UUID c681d488-d850-11d0-8c52-00c04fd90f7e (EFSRPC) or 12345778-1234-abcd-ef00-0123456789ab (LSARPC) using methods EfsRpcOpenFileRaw (opnum 0), EfsRpcEncryptFileSrv (opnum 4) or EfsRpcQueryUsersOnFile (opnum 9) from non-administrative sources.
      • Sysmon Event ID 3 (NetworkConnect) from lsass.exe on a DC to unexpected destinations on 445/tcp — a DC should not open outbound SMB sessions to non-DC servers outside defined replication partners.
      • Windows Event 4662 (Operation on object) with access masks matching LSA policy lookups from null-session or anonymous principals (SubjectUserName = "ANONYMOUS LOGON").
      • AD CS IIS access logs (/certsrv/, /certsrv/mscep/): POST requests with empty or "Mozilla/4.0" user agent, Authorization: Negotiate/NTLM, and a source IP outside the expected enrollment pool.

    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

    Windows LSA Spoofing Vulnerability

    Source: CISA KEV Catalog, NVD (NIST), cvelistv5, 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 versionsFixed in
    MicrosoftWindows Server 2008 R2 Service Pack 1
    • 6.1.7601.0 – < 6.1.7601.25685
    • 6.1.7601.25685
    MicrosoftWindows Server 2008 R2 Service Pack 1 (Server Core installation)
    • 6.1.7601.0 – < 6.1.7601.25685
    • 6.1.7601.25685
    MicrosoftWindows Server 2008 Service Pack 2
    • 6.0.6003.0 – < 6.0.6003.21192
    • 6.0.6003.21192
    MicrosoftWindows Server 2008 Service Pack 2 (Server Core installation)
    • 6.0.6003.0 – < 6.0.6003.21192
    • 6.0.6003.21192
    MicrosoftWindows Server 2012
    • 6.2.9200.0 – < 6.2.9200.23435
    • 6.2.9200.23435
    MicrosoftWindows Server 2012 (Server Core installation)
    • 6.2.9200.0 – < 6.2.9200.23435
    • 6.2.9200.23435
    MicrosoftWindows Server 2012 R2
    • 6.3.9600.0 – < 6.3.9600.20094
    • 6.3.9600.20094
    MicrosoftWindows Server 2012 R2 (Server Core installation)
    • 6.3.9600.0 – < 6.3.9600.20094
    • 6.3.9600.20094
    MicrosoftWindows Server 2016
    • 10.0.14393.0 – < 10.0.14393.4583
    • 10.0.14393.4583
    MicrosoftWindows Server 2016 (Server Core installation)
    • 10.0.14393.0 – < 10.0.14393.4583
    • 10.0.14393.4583
    MicrosoftWindows Server 2019
    • 10.0.17763.0 – < 10.0.17763.2114
    • 10.0.17763.2114
    MicrosoftWindows Server 2019 (Server Core installation)
    • 10.0.17763.0 – < 10.0.17763.2114
    • 10.0.17763.2114
    MicrosoftWindows Server version 2004
    • 10.0.0 – < 10.0.19041.1165
    • 10.0.19041.1165
    MicrosoftWindows Server version 20H2
    • 10.0.0 – < 10.0.19042.1165
    • 10.0.19042.1165

    Vendors and products

    Affected operating systems

    Affected operating systems
    Windowsmicrosoftwindows_server_200410.0.19041.1165
    Windowsmicrosoftwindows_server_2004—
    Windowsmicrosoftwindows_server_2008r2
    Windowsmicrosoftwindows_server_2008—
    Windowsmicrosoftwindows_server_2008_R26.1.7601.25685
    Windowsmicrosoftwindows_server_2008_sp26.0.6003.21192
    Windowsmicrosoftwindows_server_20126.2.9200.23435
    Windowsmicrosoftwindows_server_2012r2
    Windowsmicrosoftwindows_server_2012—
    Windowsmicrosoftwindows_server_2012_R26.3.9600.20094
    Windowsmicrosoftwindows_server_201610.0.14393.4583
    Windowsmicrosoftwindows_server_2016—
    Windowsmicrosoftwindows_server_201910.0.17763.2114
    Windowsmicrosoftwindows_server_2019—
    Windowsmicrosoftwindows_server_20H210.0.19042.1165
    Windowsmicrosoftwindows_server_20h2—

    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

    References & sources

    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).

    1. NVD analysis modifiedNVD

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Reference typeadded
      —
      Microsoft Corporation: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-36942 Types: Patch, Vendor Advisory

      Source identifier: nvd@nist.gov

    2. Record modifiedMicrosoft

      Show 6 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-36942
      Referenceremoved
      https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-36942
      —
      Referenceremoved
      https://www.kb.cert.org/vuls/id/405600
      —
      Reference typeremoved
      https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-36942 Types: Patch, Vendor Advisory
      —
      Reference typeremoved
      https://www.kb.cert.org/vuls/id/405600 Types: Exploit, Third Party Advisory, US Government Resource
      —
      Affected versions (publisher)changed
      Windows Server 2019, Windows Server 2019 (Server Core installation), Windows Server version 2004 (+12)
      Windows Server 2008 R2 Service Pack 1, Windows Server 2008 R2 Service Pack 1 (Server Core installation), Windows Server 2008 Service Pack 2 (+11)

      Source identifier: secure@microsoft.com

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