Coverage › CVE-2021-22017

CVE-2021-22017 Mapped Sigma

VMware vCenter Server Improper Access Control

Vendor / product

VMware — vCenter Server

Description (CISA)

Rhttproxy as used in vCenter Server contains a vulnerability due to improper implementation of URI normalization.

Added to KEV

2022-01-10

Due date

2022-01-24

Required action

Apply updates per vendor instructions.

Known ransomware use

Unknown

CWE

CWE-23

CISA notes

https://nvd.nist.gov/vuln/detail/CVE-2021-22017

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

T1090.001 Internal Proxy primary impact

• DET0075 Internal Proxy Behavior via Lateral Host-to-Host C2 Relay
  AN0204 Windows

  Anomalous process (e.g., rundll32, svchost, cmd) initiates connections to internal peer hosts not seen in typical communication baselines, used to proxy or forward traffic internally, often using SMB, RPC, or high ports.

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

  WinEventLog:Sysmon EventCode=1 → DC0032 Process Creation

  Windows Firewall Log SMB over high port → DC0078 Network Traffic Flow

  Tunable: InternalConnectionPattern DestinationPort TimeWindow
  AN0205 Linux

  socat, ssh, iptables, or ncat invoked from user space or cron jobs to create port forwarding, reverse shells, or inter-host tunnels between compromised Linux systems. Behavior is typically paired with socket activity and high entropy traffic.

  auditd:SYSCALL execve → DC0032 Process Creation

  NSM:Connections Internal connection logging → DC0078 Network Traffic Flow

  NSM:Flow conn.log → DC0085 Network Traffic Content

  Tunable: UserContext PortRange ProcessPattern
  AN0206 macOS

  Execution of AppleScript or Automator services launching ssh -L, socat, or launchctl items that dynamically reroute traffic from one Mac endpoint to another. LaunchAgents used to establish permanent internal tunnels.

  macos:unifiedlog None → DC0032 Process Creation

  NSM:Flow pf firewall logs → DC0078 Network Traffic Flow

  macos:osquery Process Events and Launch Daemons → DC0060 Service Creation

  Tunable: LaunchAgentPath PortBindings AppleScriptUsage
  AN0207 ESXi

  ESXi shell execution of tools/scripts (nc, socat, perl) relaying network traffic to other internal hosts, especially when initiated by unauthorized users or VMs.

  esxi:shell /var/log/shell.log → DC0032 Process Creation

  esxi:vmkernel /var/log/vmkernel.log → DC0078 Network Traffic Flow

  NSM:Flow conn.log → DC0082 Network Connection Creation

  Tunable: CLICommandPattern VMInitiator ConnectionDirectionality
  AN0208 Network Devices

  Configuration of internal NAT or proxy rules that redirect traffic between client segments internally (e.g., site-to-site port forwarding). Often used to relay internal beaconing or move traffic laterally through trust zones.

  Firewall Audit Logs Config Change → DC0051 Firewall Rule Modification

  NSM:Flow Inter-segment traffic → DC0078 Network Traffic Flow

  networkdevice:cli Policy Update → DC0064 Command Execution

  Tunable: ProxyTarget ConfigChangeUser FlowThreshold

Sigma rules tagged attack.t1090.001 (6)

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 →