Coverage › CVE-2021-21973

CVE-2021-21973 Mapped Sigma

VMware vCenter Server and Cloud Foundation Server Side Request Forgery (SSRF) Vulnerability

Vendor / product

VMware — vCenter Server and Cloud Foundation

Description (CISA)

VMware vCenter Server and Cloud Foundation Server contain a SSRF vulnerability due to improper validation of URLs in a vCenter Server plugin. This allows for information disclosure.

Added to KEV

2022-03-07

Due date

2022-03-21

Required action

Apply updates per vendor instructions.

Known ransomware use

Unknown

CWE

CWE-20, CWE-918

CISA notes

https://nvd.nist.gov/vuln/detail/CVE-2021-21973

Elsewhere

cve.org · NVD · CISA KEV · JSON

ATT&CK techniques · CTID Mappings Explorer, ATT&CK 16.1, KEV snapshot 2025-07-28

2 mapping objects across 2 techniques. exploitation technique states how the vulnerability is exploited; primary and secondary impact state what exploitation achieves. They are different claims and are labelled as such.

Detection chain · ATT&CK Enterprise v19.2 detection strategies, analytics, log sources

T1046 Network Service Discovery primary impact

• DET0376 Behavioral Detection Strategy for Network Service Discovery Across Platforms
  AN1057 Windows

  Detects processes performing network enumeration (e.g., port scans, service probing) by correlating process creation, socket connections, and sequential destination IP probing within a time window.

  WinEventLog:Sysmon EventCode=1 → DC0032 Process Creation

  WinEventLog:Sysmon EventCode=3, 22 → DC0082 Network Connection Creation

  Tunable: ScanRateThreshold KnownScannerExeList TimeWindow
  AN1058 Linux

  Detects use of network scanning utilities or scripts performing rapid connections to multiple services or hosts using auditd and netflow/pcap telemetry.

  auditd:SYSCALL execve → DC0032 Process Creation

  NSM:Flow Outbound TCP SYN or UDP to multiple ports/hosts → DC0078 Network Traffic Flow

  Tunable: PortScanThreshold ToolPatternRegex ExpectedScanSources
  AN1059 macOS

  Detects Bonjour-based mDNS enumeration or use of system tools (e.g., dns-sd, nmap) to find active services via multicast probing or targeted scans.

  macos:unifiedlog dns-sd, mDNSResponder, socket activity → DC0085 Network Traffic Content

  macos:osquery process_events → DC0032 Process Creation

  Tunable: MDNSServiceQueryPatterns UserContext ScanToolList
  AN1060 Containers

  Detects lateral discovery or container breakout attempts using netcat, curl, or custom binaries probing other services within the same namespace or VPC subnet.

  ebpf:syscalls socket connect → DC0082 Network Connection Creation

  ebpf:syscalls execve → DC0032 Process Creation

  containerd:runtime container-level outbound traffic events → DC0078 Network Traffic Flow

  Tunable: ExecutablePath TimeWindow NetworkDestinationCount

Sigma rules tagged attack.t1046 (20)

All 20 rules on the technique page →

T1190 Exploit Public-Facing Application exploitation technique

• DET0080 Exploit Public-Facing Application – multi-signal correlation (request → error → post-exploit process/egress)
  AN0219 Windows

  Adversary sends crafted HTTP/S (or other service) input to an Internet-facing app (IIS/ASP.NET, API, device portal). Chain: (1) abnormal request patterns to public endpoint → (2) elevated 4xx/5xx or unusual methods/paths → (3) server process (w3wp.exe/other service) spawns shell/LOLbins or loads non-standard modules → (4) optional outbound callback from the host/container.

  ApplicationLog:IIS IIS W3C logs in C:\inetpub\logs\LogFiles\W3SVC* (spikes in 5xx, RCE/SQLi/path traversal/JNDI patterns) → DC0038 Application Log Content

  WinEventLog:Sysmon EventCode=1 → DC0032 Process Creation

  WinEventLog:Sysmon EventCode=7 → DC0016 Module Load

  WinEventLog:Sysmon EventCode=3, 22 → DC0082 Network Connection Creation

  Tunable: PublicVIPs SuspiciousPatterns ErrorRateThreshold TimeWindow AllowedChildList
  AN0220 Linux

  Adversary exploits Apache/Nginx/app servers. Chain: (1) suspicious requests in access logs → (2) spike of 5xx or WAF blocks → (3) web server or interpreter (apache2/nginx/php-fpm/node/python) spawns /bin/sh, curl, wget, socat, or writes webshell → (4) outbound callback.

  ApplicationLog:WebServer /var/log/httpd/access_log, /var/log/apache2/access.log, /var/log/nginx/access.log with exploit indicators and burst errors → DC0038 Application Log Content

  auditd:SYSCALL execve → DC0032 Process Creation

  NSM:Flow HTTP payloads with SQLi/LFI/JNDI/deserialization indicators → DC0085 Network Traffic Content

  Tunable: WebProcList ChildToolList BurstThreshold TimeWindow
  AN0221 macOS

  Adversary targets macOS-hosted public services (e.g., nginx, node). Chain: suspicious inbound request → service crash/5xx → service spawns shell or writes file → new outbound connection.

  macos:unifiedlog App/web server logs ingested via unified logging or filebeat (nginx/apache/node). → DC0038 Application Log Content

  macos:unifiedlog exec events where web process starts a shell/tooling → DC0032 Process Creation

  NSM:Flow outbound egress from web host after suspicious request → DC0085 Network Traffic Content

  Tunable: ServiceList TimeWindow
  AN0222 Containers

  Adversary exploits containerized app via ingress or service. Chain: (1) suspicious request in ingress/app logs → (2) container process spawns a shell/exec/sidecar (kubectl exec/docker exec) → (3) egress to Internet or metadata service (169.254.169.254).

  ApplicationLog:Ingress Kubernetes NGINX/Envoy ingress controller logs with anomalous payloads and 5xx spikes → DC0038 Application Log Content

  docker:events Docker/Kubernetes audit of exec/attach (kubectl exec) or unexpected child processes inside container → DC0032 Process Creation

  NSM:Flow Requests towards cloud metadata or command & control from pod IPs → DC0085 Network Traffic Content

  Tunable: IngressNamespaces MetadataEndpoints TimeWindow
  AN0223 IaaS

  Adversary targets cloud-hosted public endpoints. Chain: (1) ALB/ELB/Cloud LB logs show exploit-like inputs or error spikes → (2) workload spawns shell or reaches metadata API → (3) egress to new external hosts.

  ALB:HTTPLogs AWS ALB/ELB/GCP/Azure Application Gateway HTTP logs with unusual methods, long URIs, serialized payloads, 4xx/5xx bursts → DC0085 Network Traffic Content

  AWS:VPCFlowLogs VPC/NSG flow logs for pod/instance egress to Internet or metadata → DC0078 Network Traffic Flow

  Tunable: LBProjects ErrorBurst
  AN0224 ESXi

  Adversary exploits exposed OpenSLP on ESXi or vCenter public endpoints. Chain: inbound request pattern to mgmt service → hostd/vpxd error/crash/restart → unexpected process behavior or datastore access → outbound callback.

  esxi:hostd /var/log/hostd.log anomalies (faults, crashes, restarts) around inbound connections → DC0038 Application Log Content

  NSM:Flow Connections to TCP 427 (SLP) or vCenter web services from untrusted sources → DC0085 Network Traffic Content

  Tunable: MgmtCIDR TimeWindow
  AN0225 Network Devices

  Adversary exploits public admin services on routers/firewalls/switches. Chain: anomalous HTTP/SNMP/SmartInstall inputs → device syslog errors/restarts → config changes/CLI spawn → egress to attacker C2.

  networkdevice:controlplane Syslog from edge devices with HTTP 500s on mgmt portal, SmartInstall events, unexpected CLI commands → DC0038 Application Log Content

  NSM:Flow NetFlow/sFlow for odd egress to Internet from mgmt plane → DC0085 Network Traffic Content

  Tunable: MgmtPorts TrustedAdmins

Sigma rules tagged attack.t1190 (149)

All 149 rules on the technique page →