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T0821 Modify Controller Tasking — Attack Simulation

Adversaries may modify the tasking of a controller to allow for the execution of their own programs. This can allow an adversary to manipulate the execution flow and behavior of a controller. According to 61131-3, the association of a Task with a Program Organization Unit (POU) defines a task association. An adversary may modify these associations or create new ones to manipulate the execution flow of a controller. Modification of controller…

Complete technique description

Adversaries may modify the tasking of a controller to allow for the execution of their own programs. This can allow an adversary to manipulate the execution flow and behavior of a controller.

According to 61131-3, the association of a Task with a Program Organization Unit (POU) defines a task association. [IEC February 2013] An adversary may modify these associations or create new ones to manipulate the execution flow of a controller. Modification of controller tasking can be accomplished using a Program Download in addition to other types of program modification such as online edit and program append.

Tasks have properties, such as interval, frequency and priority to meet the requirements of program execution. Some controller vendors implement tasks with implicit, pre-defined properties whereas others allow for these properties to be formulated explicitly. An adversary may associate their program with tasks that have a higher priority or execute associated programs more frequently. For instance, to ensure cyclic execution of their program on a Siemens controller, an adversary may add their program to the task, Organization Block 1 (OB1).

Official technique definition · Open in the interactive matrix

Detection telemetry and configuration

These contracts are selected through exact technique-to-data-component relationships or explicitly labelled planning overrides. Configure a collector at the relevant observation point; a telemetry name alone is not coverage.

Device Alarm · source-mapped

DC0108 collection page — Subscribe to supported device alarm/audit channels; retain code, severity, source asset and acknowledgement/clear times.

Providers and collection configuration

  • Agree the measurement points, read-only interfaces, sampling intervals and safety boundary with the process owner. Use a simulator or non-production fixture.
  • Subscribe to supported audit/alarm events or approved historian exports. Preserve source timestamp, quality, engineering units, asset/tag identity and clock offset.
  • Compare independent measurements and record gaps/latency. Do not enable intrusive polling, change controller logic or alter safety setpoints merely to generate logs.

Required normalized fields: asset_id, alarm_code, severity, active.

Illustrative collection event

Project-normalized synthetic JSON, not a native provider log, captured event, attack verdict or validated detection. A parser/adapter is required for a real SIEM. Example names, IPs and values are fictional.

{
  "schema": "1200km.telemetry.example.v1",
  "synthetic": true,
  "timestamp": "2026-09-27T12:00:00Z",
  "telemetry_id": "DC0108",
  "collector": "illustrative-lab-collector",
  "observation": {
    "asset_id": "lab-controller-1",
    "alarm_code": "LAB_COMM_LOSS",
    "severity": "warning",
    "active": true
  }
}

Visibility limits: There is no universal PLC event ID or configuration command. Visibility depends on vendor, protocol and process. An alarm or process deviation demonstrates an effect, not necessarily a cyberattack.

Network Traffic Content · source-mapped

DC0085 collection page — Scope approved packet capture/protocol content collection to the lab flow; retain capture provenance and truncation indicators.

Providers and collection configuration

  • Zeek: Connection and protocol metadata from traffic visible to the sensor.
  • Suricata EVE: Configured flow, alert, DNS, HTTP, TLS and protocol records.
  • Use an authorized lab TAP/SPAN, virtual mirror or gateway interface. Define which traffic crosses it; avoid assuming visibility into every segment.
  • Enable the required Zeek analyzers or Suricata EVE event types. Export logs with sensor identity, clock synchronization and flow correlation identifiers.
  • Monitor capture loss, truncation and exporter sampling. Capture payload only with approval and restrictive retention; encryption normally prevents plaintext inspection.

Required normalized fields: flow_id, protocol, method, path, payload_excerpt.

Illustrative collection event

Project-normalized synthetic JSON, not a native provider log, captured event, attack verdict or validated detection. A parser/adapter is required for a real SIEM. Example names, IPs and values are fictional.

{
  "schema": "1200km.telemetry.example.v1",
  "synthetic": true,
  "timestamp": "2026-09-27T12:00:00Z",
  "telemetry_id": "DC0085",
  "collector": "illustrative-lab-collector",
  "observation": {
    "flow_id": "lab-flow-1",
    "protocol": "http",
    "method": "GET",
    "path": "/lab-check",
    "payload_excerpt": "LAB_TELEMETRY_CHECK"
  }
}

Visibility limits: Flows are not packet payloads. NAT, asymmetric routes, encryption, missing mirrors and sampling can hide attribution or content. A destination connection alone does not prove malicious intent.

Software · source-mapped

DC0111 collection page — Collect approved engineering/asset-management software inventories and compare with the expected baseline; retain device, product, version and hash/signature provenance.

Providers and collection configuration

  • Agree the measurement points, read-only interfaces, sampling intervals and safety boundary with the process owner. Use a simulator or non-production fixture.
  • Subscribe to supported audit/alarm events or approved historian exports. Preserve source timestamp, quality, engineering units, asset/tag identity and clock offset.
  • Compare independent measurements and record gaps/latency. Do not enable intrusive polling, change controller logic or alter safety setpoints merely to generate logs.

Required normalized fields: asset_id, software, version, expected_version, sha256.

Illustrative collection event

Project-normalized synthetic JSON, not a native provider log, captured event, attack verdict or validated detection. A parser/adapter is required for a real SIEM. Example names, IPs and values are fictional.

{
  "schema": "1200km.telemetry.example.v1",
  "synthetic": true,
  "timestamp": "2026-09-27T12:00:00Z",
  "telemetry_id": "DC0111",
  "collector": "illustrative-lab-collector",
  "observation": {
    "asset_id": "lab-engineering-1",
    "software": "Lab HMI runtime",
    "version": "1.0-lab",
    "expected_version": "1.0-lab",
    "sha256": "dddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd"
  }
}

Visibility limits: There is no universal PLC event ID or configuration command. Visibility depends on vendor, protocol and process. An alarm or process deviation demonstrates an effect, not necessarily a cyberattack.

Detection rules and analytic guidance

Open the dedicated detection workspace · Existing query engineering

DET0741 Detection of Modify Controller Tasking

MITRE detection strategy

AN1874 Analytic 1874

Real-time monitoring identifies an Industrial Control System (ICS) protocol write to a controller's task/organization-block configuration from a source not in the approved engineering workstation list, correlated against post-modification cycle timing deviation. Documented precedent: Stuxnet infected Siemens OB1 (main execution cycle block) so its malicious payload ran every cycle, and infected OB35 (watchdog/interrupt block) to suppress error reporting. OT operational-fidelity gate: Alert only when the action is not attributable to an authorized operator/engineering source for the specific target and function, and it is either outside an approved change/maintenance window or lacks matching change-control context; where telemetry permits, require corroborating device, configuration, or process-state effect. Suppress activity that fully matches approved maintenance, commissioning, failover, recovery, or tested control procedures.

Platforms: Embedded.

  • Software — assetinventory:ProgramDiff; channel current task-to-block assignment table differs from last known-good baseline without corresponding change ticket.
  • Network Traffic Content — NSM:Content; channel task/organization-block modification service from source not in engineering workstation list outside change control window.
  • Device Alarm — device:VendorLog; channel measured scan cycle time or interrupt response latency deviates from baseline cycle time by more than cycle timing deviation threshold following a task configuration change.
Source rule directory and observation requirements

No exact-tagged Sigma source rule was imported. This does not establish that the technique is undetectable; the MITRE guidance and collection requirements remain relevant.

Before treating a rule as coverage

  1. Read the actual condition and logsource; identify attacker-side, victim-side or third-party visibility.
  2. Map native sensor fields, parse times and identities, then compile for the selected backend.
  3. Replay a behavior-positive case, a normal control, an authorized look-alike and a missing-telemetry case.
  4. Record matches and misses with rule version and source events. No match is inconclusive when required telemetry is absent.

Anomaly-based detection

No exact technique-specific Atlas model is present for T0821 in the selected source snapshot. The following is a design worksheet, not a newly validated model.

Anomaly engineering worksheet

Start from the exact analytic above. The collection-specific lenses below are analyst recommendations; they do not assert that an arbitrary statistical deviation detects this technique.

  • Industrial operations and physical process: Per asset, operating mode and engineering change window: deviations in command/state sequences, measurement residuals and communication freshness. Use a simulator or approved test rig; never generate hazardous physical effects.
  • Network and protocol telemetry: Per source and observation point: connection rate, destination-host/port fan-out, response/failure ratio and previously unseen destinations. Compare equivalent time windows; separate authorized scanners, NAT and sampling effects.
  1. Define an entity/peer group and feature; exclude the evaluation period from baseline training.
  2. Use representative normal and maintenance activity. Do not invent a production threshold from a synthetic example.
  3. Evaluate held-out behavior-positive and benign cases; measure false positives, misses and telemetry loss separately.
  4. Keep abnormality separate from maliciousness. Correlate with the behavior-specific source evidence.

Anomaly Detection Atlas · Baseline, validation and blind spots

Attack tools and documented software

No reviewed lab-tool association is selected for this exact technique. This is a curation gap, not a statement that no tool can implement the behavior.

Software observed in source procedures

These are exact ATT&CK software-use relationships, including malware. They provide behavior context, not recommendations to download or execute malware. No safety or detector claim is inherited.

3 source-documented software associations

Simulation design and documented procedures

Atomic evidence: no compatible candidate in this snapshot. Live lab status: not run for these imported procedures.

Use a process simulator or isolated test rig with no connection to production controllers or physical actuators. Preserve safety interlocks; destructive effects require synthetic evidence, not real equipment damage.

No compatible Atomic procedure is present in this pinned evidence set. Technical feasibility has not been ruled out. A custom procedure must define the behavior, target, collection point, success observable and rollback before execution.

Technique-specific experiment contract

  1. Choose one procedure implementing T0821 Modify Controller Tasking; identify the observable behavior in the source definition, not just its tactic.
  2. Record exact target, tool/version, inputs, privileges, network limits and approval. Never run an imported default target automatically.
  3. Enable the collection sources above and verify a benign baseline reaches the detector.
  4. Run only the approved isolated scenario; capture native events and an independent behavior observable.
  5. Evaluate the exact rule/model, restore the lab, and preserve configuration, event hashes, alerts, controls and misses.

Synthetic logs and offline contract check

Download synthetic collection fixture (JSON) · Download the complete engineering workbook

This fixture exercises the listed collection fields. It does not reproduce Modify Controller Tasking, label its example events as malicious, or measure detection effectiveness. Use the exact analytic and selected procedure to build an independently labelled behavior-positive dataset.

Not run in this browser. No network scan or attack command is executed by this control.

Validation status and remaining work

Source identity
Joined by exact technique/object IDs against hash-pinned sources.
Collection fixture
Available for offline schema exercises; not attack emulation.
Native telemetry / backend / real attack
Not validated for these imported procedures. Source fidelity and page tests cannot establish sensor or detector effectiveness.

All-page audit and evidence inventory · This page’s machine-readable workbook

Sources and evidence boundaries

Pinned MITRE STIX source · SHA-256 c9ca0ce523a1b5e512060a390415e8aefe8f6d32c5f82d7de81264960c1e1183. Definition and procedure context are reproduced from this snapshot, not independently re-investigated incidents.

Source-linked mitigations
  • M0800 Authorization Enforcement

    All field controllers should restrict the modification of controller tasks to only certain users (e.g., engineers, field technician), preferably through implementing a role-based access mechanism.

  • M0804 Human User Authentication

    All field controllers should require users to authenticate for all remote or local management sessions. The authentication mechanisms should also support Account Use Policies, Password Policies, and User Account Management.

  • M0945 Code Signing

    Utilize code signatures to verify the integrity and authenticity of programs installed on safety or control assets, including the associated controller tasking.

  • M0947 Audit

    Provide the ability to verify the integrity of controller tasking. While techniques like CRCs and checksums are commonly used, they are not cryptographically secure and can be vulnerable to collisions. Preferably cryptographic hash functions (e.g., SHA-2, SHA-3) should be used. [IEC February 2019]

Connected ecosystem references

Linked tags

icsics-otEmbeddedexecutionisolated_authorized_labprocedure_review_requiredtelemetry_configuration_requiredot_fixture_and_process_safety_review
No Atomic candidate in snapshottechniquesource_mapped

Detection and collection

T0821 detection workspace

No reviewed association in this snapshot.

Pinned research references. No browser attack runner or production-validated detector is asserted. Imported procedures remain unvalidated; any bounded lab evidence has its own scope. ATT&CK / Atomic provenance · Detection provenance.