CriticalCVE-2021-42278

    Active Directory Domain Services Elevation of Privilege Vulnerability (CVE-2021-42278)

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

    What is affected, what to do

    Active Directory Domain Services Elevation of Privilege 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 6.1.7601.25769, Microsoft Windows Server 2008 R2 Service Pack 1 (Server Core installation) to version 6.1.7601.25769, Microsoft Windows Server 2008 Service Pack 2 to version 6.0.6003.21282. 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..6.1.7601.25769
    • Microsoft Windows Server 2008 R2 Service Pack 1 (Server Core installation) lt 6.1.7601.0..6.1.7601.25769
    • Microsoft Windows Server 2008 Service Pack 2 lt 6.0.6003.0..6.0.6003.21282
    • Microsoft Windows Server 2008 Service Pack 2 (Server Core installation) lt 6.0.6003.0..6.0.6003.21282
    • Microsoft Windows Server 2012 lt 6.2.9200.0..6.2.9200.23517
    • Microsoft Windows Server 2012 (Server Core installation) lt 6.2.9200.0..6.2.9200.23517
    • Microsoft Windows Server 2012 R2 lt 6.3.9600.0..6.3.9600.20174
    • Microsoft Windows Server 2012 R2 (Server Core installation) lt 6.3.9600.0..6.3.9600.20174
    • Microsoft Windows Server 2016 lt 10.0.14393.0..10.0.14393.4770
    • Microsoft Windows Server 2016 (Server Core installation) lt 10.0.14393.0..10.0.14393.4770
    • Microsoft Windows Server 2019 lt 10.0.17763.0..10.0.17763.2300
    • Microsoft Windows Server 2019 (Server Core installation) lt 10.0.17763.0..10.0.17763.2300
    • Microsoft Windows Server 2022 lt 10.0.20348.0..10.0.20348.350
    • Microsoft Windows Server version 2004 lt 10.0.0..10.0.19041.1348
    • Microsoft Windows Server version 20H2 lt 10.0.0..10.0.19042.1348
    Fixed in
    • Microsoft Windows Server 2008 R2 Service Pack 1 6.1.7601.25769
    • Microsoft Windows Server 2008 R2 Service Pack 1 (Server Core installation) 6.1.7601.25769
    • Microsoft Windows Server 2008 Service Pack 2 6.0.6003.21282
    • Microsoft Windows Server 2008 Service Pack 2 (Server Core installation) 6.0.6003.21282
    • Microsoft Windows Server 2012 6.2.9200.23517
    • Microsoft Windows Server 2012 (Server Core installation) 6.2.9200.23517
    • Microsoft Windows Server 2012 R2 6.3.9600.20174
    • Microsoft Windows Server 2012 R2 (Server Core installation) 6.3.9600.20174
    • Microsoft Windows Server 2016 10.0.14393.4770
    • Microsoft Windows Server 2016 (Server Core installation) 10.0.14393.4770
    • Microsoft Windows Server 2019 10.0.17763.2300
    • Microsoft Windows Server 2019 (Server Core installation) 10.0.17763.2300
    • Microsoft Windows Server 2022 10.0.20348.350
    • Microsoft Windows Server version 2004 10.0.19041.1348
    • Microsoft Windows Server version 20H2 10.0.19042.1348

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    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

    73.3 %

    EPSS score

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

    Source: FIRST EPSS, percentile 99.46

    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
    241.64 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
    73.3 %
    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
    99.46
    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 9 November 2021

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This CVE sits on KEV and is explicitly flagged by CISA as used in ransomware intrusions, because chained with CVE-2021-42287 it collapses the gap between any authenticated domain user and Domain Admin to a single tool invocation. The CVSS vector is network-reachable and only needs low privileges — a single phished mailbox or weak service account is enough — which places exploitation likelihood in the top tier of all tracked vulnerabilities. For any NIS2-regulated organisation operating on-prem Active Directory this is an unconditional P1: an unpatched DC is operationally equivalent to an open Domain Admin console, with Tier-0 blast radius across Exchange, ADFS, SCCM and backup infrastructure. Sequence of action: verify the November 2021 cumulative on DCs before any other workload, then enforce PacRequestorEnforcement=2 and MachineAccountQuota=0.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Deploy the Microsoft November 2021 cumulative on EVERY domain controller: KB5008380 (Server 2019), KB5008602 (Server 2022), KB5008601 (Server 2016), KB5008263/KB5008277 (Server 2012 R2 / 2012), KB5008274/KB5008271 (Server 2008 R2 SP1). This takes priority over all other workloads — chained with CVE-2021-42287 ("noPac"), the flaw yields Domain Admin from any ordinary user account in seconds.
      • After patching, set HKLM\SYSTEM\CurrentControlSet\Services\Kdc\PacRequestorEnforcement = 2 on every DC to force the new PAC validation into enforcement mode. Without it the fix stays in audit-only and does not block exploitation.
      • Reduce ms-DS-MachineAccountQuota to 0 immediately (Set-ADDomain -Replace @{"ms-DS-MachineAccountQuota"=0}). The default of 10 lets any authenticated user create the computer object the exploit depends on.
      • Verify patch state on all DCs (Get-HotFix -Id KB5008380 etc.); remove unpatched DCs from FSMO roles and, if necessary, from replication until they are current.
      • Hunt for anomalous computer objects now: Get-ADComputer -Filter * -Properties sAMAccountName,servicePrincipalName | Where-Object { $_.sAMAccountName -notlike "*$" }. Any computer account whose sAMAccountName lacks the trailing $ is highly suspicious.
      • Prepare a KRBTGT double-rotation plan (two resets more than 10 h apart) in case the hunt surfaces indicators of prior compromise.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: enforce the Tier-0 model. Kerberos (TCP/UDP 88, 464) and LDAP (389/636/3268/3269) to DCs must be reachable only from defined admin jump hosts and legitimate member servers while any DC still runs in audit mode.
      • IAM hardening: ms-DS-MachineAccountQuota = 0 domain-wide, delegate "Create Computer Objects" solely to a dedicated OU admin account, and place all Tier-0 identities in the Protected Users group.
      • Audit policy: enable "Audit Kerberos Authentication Service" and "Audit Kerberos Service Ticket Operations" (Success+Failure) and "Audit Computer Account Management" (Success). The detections below depend on these event sources.
      • Endpoint hardening: deploy LAPS on all member servers, disable local admin accounts, enable LSASS protection (RunAsPPL) and Credential Guard across Tier-0 and Tier-1 systems.
      • EDR rule: block execution of samba-tool, Impacket modules (addcomputer.py, ticketer.py, getST.py, noPac.py) and PowerShell routines calling New-MachineAccount on non-admin workstations.
      • Change control for computer object renames: a SCOM watcher or scheduled script that escalates every sAMAccountName rename on a computer object. Legitimate renames are extremely rare.

    3. Runbook step 3

      Detection rules

      • Event ID 4741 (Computer Account Created) followed within seconds by 4742 (Computer Account Changed) that modifies sAMAccountName to a value without a trailing $, especially one matching an existing DC name (e.g. DC01 instead of DC01$). Sigma shape: EventID: 4742 AND TargetUserName|endswith: 'DC*' without $ suffix.
      • Event ID 4769 issuing a TGS for a high-privilege service to a principal that was renamed moments earlier — correlate UserPrincipalName against sAMAccountName history captured by Event 5136 (Directory Service Changes on attribute sAMAccountName).
      • KQL for Microsoft Defender for Identity / 365 Defender: IdentityDirectoryEvents | where ActionType == "Account Name Changed" and TargetAccountDisplayName endswith "$" and PreviousAccountDisplayName !endswith "$" — also check the inverse case.
      • Event ID 4662 where Properties includes {bf967a86-0de6-11d0-a285-00aa003049e2} (computer object class) and Operation "Write Property" on sAMAccountName by a non-Tier-0 account.
      • Network telemetry (Zeek kerberos.log): TGS-REQ with cname set to a computer account lacking $, requesting sname krbtgt. Baseline should be empty; any hit warrants immediate triage.
      • Microsoft Defender for Identity emits "Suspected AS-REQ with changed sAMAccountName" and "Suspicious modification of a sAMNameAccount attribute" out of the box — forward both to SIEM at P1 severity.

    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

    Active Directory Domain Services Elevation of Privilege Vulnerability

    Source: cvelistv5, CISA KEV Catalog, NVD (NIST), 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 – < 6.1.7601.25769
    • 6.1.7601.25769
    MicrosoftWindows Server 2008 R2 Service Pack 1 (Server Core installation)
    • 6.1.7601.0 – < 6.1.7601.25769
    • 6.1.7601.25769
    MicrosoftWindows Server 2008 Service Pack 2
    • 6.0.6003.0 – < 6.0.6003.21282
    • 6.0.6003.21282
    MicrosoftWindows Server 2008 Service Pack 2 (Server Core installation)
    • 6.0.6003.0 – < 6.0.6003.21282
    • 6.0.6003.21282
    MicrosoftWindows Server 2012
    • 6.2.9200.0 – < 6.2.9200.23517
    • 6.2.9200.23517
    MicrosoftWindows Server 2012 (Server Core installation)
    • 6.2.9200.0 – < 6.2.9200.23517
    • 6.2.9200.23517
    MicrosoftWindows Server 2012 R2
    • 6.3.9600.0 – < 6.3.9600.20174
    • 6.3.9600.20174
    MicrosoftWindows Server 2012 R2 (Server Core installation)
    • 6.3.9600.0 – < 6.3.9600.20174
    • 6.3.9600.20174
    MicrosoftWindows Server 2016
    • 10.0.14393.0 – < 10.0.14393.4770
    • 10.0.14393.4770
    MicrosoftWindows Server 2016 (Server Core installation)
    • 10.0.14393.0 – < 10.0.14393.4770
    • 10.0.14393.4770
    MicrosoftWindows Server 2019
    • 10.0.17763.0 – < 10.0.17763.2300
    • 10.0.17763.2300
    MicrosoftWindows Server 2019 (Server Core installation)
    • 10.0.17763.0 – < 10.0.17763.2300
    • 10.0.17763.2300
    MicrosoftWindows Server 2022
    • 10.0.20348.0 – < 10.0.20348.350
    • 10.0.20348.350
    MicrosoftWindows Server version 2004
    • 10.0.0 – < 10.0.19041.1348
    • 10.0.19041.1348
    MicrosoftWindows Server version 20H2
    • 10.0.0 – < 10.0.19042.1348
    • 10.0.19042.1348

    Vendors and products

    Affected operating systems

    Affected operating systems
    Windowsmicrosoftwindows_server_200410.0.19041.1348
    Windowsmicrosoftwindows_server_2004—
    Windowsmicrosoftwindows_server_2008r2
    Windowsmicrosoftwindows_server_2008—
    Windowsmicrosoftwindows_server_2008_R26.1.7601.25769
    Windowsmicrosoftwindows_server_2008_sp26.0.6003.21282
    Windowsmicrosoftwindows_server_20126.2.9200.23517
    Windowsmicrosoftwindows_server_2012r2
    Windowsmicrosoftwindows_server_2012—
    Windowsmicrosoftwindows_server_2012_R26.3.9600.20174
    Windowsmicrosoftwindows_server_201610.0.14393.4770
    Windowsmicrosoftwindows_server_2016—
    Windowsmicrosoftwindows_server_201910.0.17763.2300
    Windowsmicrosoftwindows_server_2019—
    Windowsmicrosoftwindows_server_202210.0.20348.350
    Windowsmicrosoftwindows_server_2022—
    Windowsmicrosoftwindows_server_20H210.0.19042.1348
    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
    PoC-in-GitHub (nomi-sec)noPac (opens in a new tab)github.comPoC (publicly reported)reported, not verified

    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. Record modifiedMicrosoft

      Show 4 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-42278
      Referenceremoved
      https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42278
      —
      Reference typeremoved
      https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42278 Types: Patch, Vendor Advisory
      —
      Affected versions (publisher)changed
      Windows Server 2019, Windows Server 2019 (Server Core installation), Windows Server 2022 (+13)
      Windows Server 2008 R2 Service Pack 1, Windows Server 2008 R2 Service Pack 1 (Server Core installation), Windows Server 2008 Service Pack 2 (+12)

      Source identifier: secure@microsoft.com

    2. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: active, automatable: no

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      SSVC assessmentchanged
      {"id":"CVE-2021-42278","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2025-02-04T18:05:48.311573Z"}
      {"id":"CVE-2021-42278","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2021-11-09T00:00:00+00:00"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

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    <a href="https://intel.neosec.eu/en/cve/CVE-2021-42278"><img src="https://intel.neosec.eu/badge/cve/CVE-2021-42278.svg?lang=en" alt="CVE-2021-42278 – NEOSEC Intel" height="20"></a>