CriticalCVE-2021-21972

    VMware vCenter Server Remote Code Execution Vulnerability (CVE-2021-21972)

    Published In CISA KEV since Sources: SingCERT, CVE.org

    What is affected, what to do

    This vulnerability allows an attacker with network access to port 443 to execute commands with unrestricted privileges on the underlying operating system hosting vCenter Server, through a Remote Code Execution (RCE) in a vCenter Server plugin. It affects VMware vCenter Server versions 7.x before 7.0 U1c, 6.7 before 6.7 U3l, and 6.5 before 6.5 U3n, as well as VMware Cloud Foundation versions 4.x before 4.2 and 3.x before 3.10.1.2. The vulnerability is actively exploited in ransomware campaigns. Immediate patching to the specified versions is crucial to mitigate this risk.

    The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. Update cloud_foundation to version 3.10.1.2. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • VMware vCenter Server eq 7.x before 7.0 U1c..7.x before 7.0 U1c
    • VMware vCenter Server eq 6.7 before 6.7 U3l..6.7 before 6.7 U3l
    • VMware vCenter Server eq 6.5 before 6.5 U3n..6.5 before 6.5 U3n
    • VMware Cloud Foundation eq 4.x before 4.2..4.x before 4.2
    • VMware Cloud Foundation eq 3.x before 3.10.1.2..3.x before 3.10.1.2

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

    Metrics

    9.8

    Priority

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

    Source: NVD, CVSS v3

    9.8

    CVSS v3

    Severity Critical on the scale from 0 to 10.

    Source: SingCERT, CVE.org

    99.87 %

    EPSS score

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

    Source: FIRST EPSS, percentile 99.96

    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
    253.94 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: ANSSI / CERT-FR, CSA/SingCERT 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
    9.8 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
    9.8
    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
    99.87 %
    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
    99.96
    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

    Response and mitigation

    Why act now?

    Prioritisation rationale

    The flaw is exploitable unauthenticated over port 443 and yields code execution as root/SYSTEM on one of the most critical management components of any VMware estate — whoever owns vCenter owns every attached ESXi host and effectively every VM. Exploit likelihood is among the very highest in the entire KEV catalogue, public exploits have been trivially available since 2021, and CISA flags active use in ransomware campaigns, particularly for hypervisor-level encryption. For NIS2-regulated and KRITIS operators, any ungepatched vCenter reachable from the user LAN — let alone the internet — is a P1 incident; even purely internal instances belong in the next maintenance window, because lateral movement from a compromised client subnet is the standard attack path here.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Deploy the vendor patch: vCenter Server 7.0 U1c, 6.7 U3l or 6.5 U3n (Cloud Foundation 4.2 / 3.10.1.2) per VMware advisory VMSA-2021-0002. This is the only full fix.
      • If patching has to wait, apply the VMSA-2021-0002 workaround — set the vROps plugin to incompatible in /etc/vmware/vsphere-ui/compatibility-matrix.xml and restart the vsphere-ui service. Verify /ui/vropspluginui/rest/services/* now returns 404.
      • Remove port 443/TCP of the vCenter appliances from every network that is not an admin segment; allow access only from a jump host or admin bastion. No exposure to user LAN, OT segments or the internet.
      • Forensically triage before you merely patch: check /usr/lib/vmware-vsphere-ui/server/work/deployer/s/global/*/0/h5ngc.war/resources/uploads/ for unknown files and /var/log/vmware/vsphere-ui/logs/vsphere_client_virgo.log for POST requests against /ui/vropspluginui/rest/services/uploadova.
      • Rotate every service account registered inside vCenter (AD join account, SSO administrator, backup integration, storage providers) after patching — RCE as root/SYSTEM means credentials on the host must be considered stolen.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: place vCenter in a dedicated management VLAN; inbound 443/TCP only from a named admin source list, deny all else. ESXi hosts talk outbound to vCenter (443/902), never the inverse direction.
      • Reverse proxy / WAF in front of the vSphere Client: block the path /ui/vropspluginui/rest/services/uploadova and more broadly POSTs to /ui/*plugin*/rest/services/* while the workaround is in place. Disallow multipart uploads to the vSphere UI entirely.
      • Egress control on the appliance: allowlist outbound traffic to vCenter-required destinations only (NTP, DNS, AD, repo, syslog, SMTP). Any connection from the appliance to Pastebin, raw.githubusercontent, unknown IPs or TOR exit nodes is an IOC.
      • IAM hardening: treat administrator@vsphere.local as break-glass only; daily admin work via named AD accounts with role bindings. Enforce MFA via identity federation (ADFS, Entra ID, Keycloak) before the SSO login.
      • Snapshot and back up the appliance before patching; store configuration backups offline. Rehearse the rollback path.
      • Centralise logging: ship vSphere-UI logs, vpxd and SSO logs by syslog to the SIEM; add auditd for shell-level visibility on the appliance.

    3. Runbook step 3

      Detection rules

      • Web access log signature: POST to /ui/vropspluginui/rest/services/uploadova returning 200/405 — direct exploit indicator. Sigma shape: selection: cs-uri-stem|contains: '/vropspluginui/rest/services/uploadova' and cs-method: POST.
      • File-system monitoring (auditd / EDR) for new .jsp, .war or shell scripts under /usr/lib/vmware-vsphere-ui/server/work/ and /tmp/; a tomcat/java process spawning sh, bash or python on the appliance is not legitimate.
      • Network: outbound reverse shells from the vCenter IP to non-standard ports (anything outside the normal 53/80/123/389/443/636 to known destinations). Zeek conn.log: id.orig_h == vcenter and id.resp_p not in (allowlist).
      • Linux auditd / Sysmon-for-Linux: execve of whoami, id, uname -a, cat /etc/shadow under the vsphere-ui service UID — classic post-exploitation recon.
      • SIEM correlation: within 10 minutes of a POST to /ui/vropspluginui/*, a new child process under vsphere-ui or a new outbound TCP session from the appliance. KQL shape: DeviceProcessEvents | where InitiatingProcessParentFileName in ("java","tomcat") and FileName in ("sh","bash","python","nc","curl","wget").

    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 vSphere Client (HTML5) contains a remote code execution vulnerability in a vCenter Server plugin. A malicious actor with network access to port 443 may exploit this issue to execute commands with unrestricted privileges on the underlying operating system that hosts vCenter Server. This affects VMware vCenter Server (7.x before 7.0 U1c, 6.7 before 6.7 U3l and 6.5 before 6.5 U3n) and VMware Cloud Foundation (4.x before 4.2 and 3.x before 3.10.1.2).

    Source: CSA/SingCERT, CISA KEV Catalog, cvelistv5, NVD (NIST)

    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
    —VMware Cloud Foundation
    • 3.x before 3.10.1.2
    • 4.x before 4.2
    • —
    • —
    —VMware vCenter Server
    • 6.7 before 6.7 U3l
    • 7.x before 7.0 U1c
    • 6.5 before 6.5 U3n
    • —
    • —
    • —
    vmwarecloud_foundation
    • 3.0 – < 3.10.1.2
    • 4.0 – < 4.2
    • 3.10.1.2
    • 4.2
    vmwarevcenter_server
    • 6.7
    • 7.0
    • 6.5
    • —
    • —
    • —

    Vendors and products

    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
    CSA/SingCERTMultiple High-Risk Vulnerabilities in VMware Products (opens in a new tab)CSA/SingCERTactively exploited
    ANSSI / CERT-FRLicence Ouverte 2.0, as of CERTFR-2021-ALE-003 – [MàJ] Vulnérabilité dans VMware vCenter Server (clôturée 2021-05-12) (opens in a new tab)cert.cyber.gouv.fractively exploited
    Packet StormVMware vCenter Server 7.0 Arbitrary File Upload (opens in a new tab)packetstormsecurity.comPoC (publicly reported)reported, not verified—
    Packet StormVMware vCenter Server File Upload Remote Code Execution (opens in a new tab)packetstormsecurity.comPoC (publicly reported)reported, not verified—
    Packet StormVMware vCenter 6.5 6.7 7.0 Remote Code Execution (opens in a new tab)packetstormsecurity.comPoC (publicly reported)reported, not verified—
    PoC-in-GitHub (nomi-sec)CVE-2021-21972 (opens in a new tab)github.comPoC (publicly reported)reported, not verified

    References & sources

    • vmware.comsecurity/advisories/VMSA-2021-0002.htmlx_refsource_CONFIRM
    • packetstormsecurity.comfiles/161590/VMware-vCenter-Server-7.0-Arbitrary-File-Upload.ht…x_refsource_MISC
    • packetstormsecurity.comfiles/161695/VMware-vCenter-Server-File-Upload-Remote-Code-Exec…x_refsource_MISC
    • packetstormsecurity.comfiles/163268/VMware-vCenter-6.5-6.7-7.0-Remote-Code-Execution.h…x_refsource_MISC
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2021-21972government-resource
    • cert.cyber.gouv.frANSSI / CERT-FR: CERTFR-2021-ALE-003 – [MàJ] Vulnérabilité dans VMware vCenter Server (clôturée 2021-05-12)cert-fr
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