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NET-21: Denial of Service (DoS) Protection

NET 9 — Critical Protect

Automated mechanisms exist to protect against or limit the effects of denial of service attacks.

Renumbered: Formerly NET-02.1 in SCF 2025.4.

Control Question: Does the organization use automated mechanisms to protect against or limit the effects of denial of service attacks?

General (21)
Framework Mapping Values
CSA IoT SCF 2 OPA-08 OPA-09
GovRAMP SC-05
GovRAMP Low SC-05
GovRAMP Low+ SC-05
GovRAMP Moderate SC-05
GovRAMP High SC-05
IEC 62443-3-3 2013 SR 7.1 SR 7.1 RE 1 SR 7.1 RE 2
IEC 62443-4-2 2019 CR 7.1 CR 7.1(1)
MITRE ATT&CK 16 T1496.003
NIST 800-53 R4 SC-5
NIST 800-53 R5.2 SC-05
NIST 800-53B R5 (low) (source) SC-05
NIST 800-53B R5 (moderate) (source) SC-05
NIST 800-53B R5 (high) (source) SC-05
NIST 800-82 R3 SC-05
NIST 800-82 R3 LOW OT Overlay SC-05
NIST 800-82 R3 MODERATE OT Overlay SC-05
NIST 800-82 R3 HIGH OT Overlay SC-05
NIST 800-161 R1 SC-5
NIST 800-172 R3 03.13.12E
NIST 800-172A R3 DS-A.03.13.12E.a A.03.13.12E.ODP[01] A.03.13.12E.ODP[02] DS-A.03.13.12E.b A.03.13.12E.ODP[03]
US (10)
EMEA (2)
Framework Mapping Values
EMEA Germany C5 2026 COS-01.02B.2
EMEA Saudi Arabia CSCC-1 2019 2-4-1-8
APAC (6)
Framework Mapping Values
APAC Australia ISM June 2026 ISM-1019 ISM-1431 ISM-1436 ISM-1805
APAC India RBI Digital Payments 2021 15.0 51.0
APAC Malaysia RMiT 2025 A5-A6 A5-A6(a) A5-A6(b) A5-E1(b) A10-B11(a) A10-B11(b)
APAC New Zealand HISF Microsmall 2023 HMS17
APAC New Zealand NZISM 3.9 18.3.18.C.01 18.3.19.C.01
APAC Singapore CCOP CII 2026 4.1.1(i) 12.1.1(i)
Americas (1)
Framework Mapping Values
Americas Bermuda BMACCC 2020 6.19

Capability Maturity Model

Level 0 — Not Performed

Practices are non-existent, based on the inability to demonstrate an implemented and operational capability. A reasonable person would conclude the control is not being performed.

Level 1 — Performed Informally

SCR-CMM Level 1 criteria definitions are not available for this control: ▪ A reasonable person would conclude this control requires a structured process. ▪ At this level of maturity, the "ad hoc" nature of performing a capability informally would indicate the intent of the control is not met due to a lack of consistency and formality.

Level 2 — Planned & Tracked

Network Security (NET) capabilities are requirements-driven, but are not standardized across the entity (e.g., local/regional level consistency). Capability criteria associated with this control reasonably expect the following criteria to exist: ▪ Policies and standards associated with NET domain capabilities are formally documented and centrally-managed by the entity. ▪ Standardized Operating Procedures (SOP) associated with NET domain capabilities are documented and maintained by process owners. ▪ IT and/or cybersecurity personnel work with business stakeholders and process owners to appropriately scope and reasonably implement cybersecurity and data protection controls associated with NET domain capabilities to address applicable statutory, regulatory and/or contractual requirements for Technology Assets, Applications, Services and/or Data (TAASD). ▪ Network security-related controls are primarily administrative and preventative in nature (e.g., policies, standards and procedures & guidelines). ▪ Network security management may be a defined function (e.g., team or department) or assigned as an additional duty to existing IT and/or cybersecurity personnel. ▪ IT personnel define secure networking practices to protect the Confidentiality, Integrity, Availability and Safety (CIAS) of the organization's TAASD. ▪ Secure Baseline Configurations (SBC) enforce the principles of least privileges and least functionality for boundary protection technologies. ▪ Boundary protection technologies minimize the effect of Denial of Service (DoS) attacks against business-critical services.

Level 3 — Well Defined

Network Security (NET) capabilities are standardized across the entity for applicability to People, Processes, Technologies, Data and/or Facilities (PPTDF) to ensure consistency for Technology Assets, Applications, Services and/or Data (TAASD). Capability criteria associated with this control reasonably expect the following criteria to exist: ▪ Policies and standards associated with NET domain capabilities are formally documented and centrally-managed by the entity's Governance, Risk & Compliance (GRC) team, or similar function. ▪ Standardized Operating Procedures (SOP) associated with NET domain capabilities are well-documented and kept current by process owners. ▪ A network security management team, or similar function, is appropriately staffed and supported to implement and maintain NET domain capabilities. ▪ Technology is leveraged to enhance the efficiency and accuracy of network security operations (e.g., network management solution and log aggregator). ▪ The entity's Governance, Risk & Compliance (GRC) team, or similar function, works with business stakeholders and process owners to appropriately scope and reasonably implement cybersecurity and data protection controls associated with NET domain capabilities to address Minimum Compliance Requirements (MCR) (e.g., applicable statutory, regulatory and/or contractual requirements) and Discretionary Security Requirements (DSR) (e.g., entity-required controls). ▪ Secure Baseline Configurations (SBC) enforce the principles of least privileges and least functionality for boundary protection technologies. ▪ An implemented and operational capability exists to automatically protect against or limit the effects of denial of service attacks.

Level 4 — Quantitatively Controlled

Network Security (NET) capabilities, in addition to being standardized across the entity and centrally managed to ensure consistency across Technology Assets, Applications, Services and/or Data (TAASD), efforts are metrics driven to provide sufficient insight for decision makers to predict optimal performance, ensure continued operations and/or identify areas for improvement. Capability criteria associated with this control reasonably expect the following criteria to exist: ▪ Applicable SCR-CMM Level 3 (Well Defined) capabilities are implemented and operational. ▪ Metrics reporting includes quantitative analysis of Key Performance Indicators (KPIs). ▪ Metrics reporting includes quantitative analysis of Key Risk Indicators (KRIs). ▪ Scope of metrics, KPIs and KRIs covers organization-wide cybersecurity and data protection controls, including functions performed by third-parties. ▪ Organizational leadership maintains a formal process to objectively review and respond to metrics, KPIs and KRIs (e.g., monthly or quarterly review). ▪ Based on metrics analysis, process improvement recommendations are submitted for review and are handled in accordance with change control processes. ▪ Business and technical stakeholders are involved in reviewing and approving proposed changes to evolve capabilities.

Level 5 — Continuously Improving

Utilize SCR-CMM Level 3 or Level 4 (if available) criteria definitions: ▪ There are no defined Level 5 criteria, since it is reasonable to assume a continuously-improving process is not necessary to operationalize this control. ▪ Level 5 capabilities should be considered “world-class” where the control builds on Level 4 capabilities, but are continuously improving through Artificial Intelligence (AI) and/or Machine Learning (ML) technologies. ▪ While it may be possible to develop responsive capabilities for this control through the use of AI and/or ML technologies, the criteria would be organization-specific to define.

Assessment Objectives

  1. NET-21_A01 types of denial-of-service events to be protected against or limited are defined.
  2. NET-21_A02 resource prioritization is designed to limit negative effects of denial-of-service events.
  3. NET-21_A03 controls to achieve the denial-of-service objective by type of denial-of-service event are defined.
  4. NET-21_A04 controls by type of denial-of-service event are employed to achieve the denial-of-service protection objective.
  5. NET-21_A05 the ability of individuals to launch denial-of-service attacks against other systems is restricted.
  6. NET-21_A06 the effects of types of denial-of-service events are organizationally-defined.
  7. NET-21_A07 capacity, bandwidth or other redundancies to limit the effects of information flooding denial-of-service attacks are managed.
  8. NET-21_A08 monitoring tools for detecting indicators of denial-of-service attacks are defined.
  9. NET-21_A09 system resources to be monitored to determine if sufficient resources exist to prevent effective denial-of-service attacks are defined.
  10. NET-21_A10 monitoring tools are employed to detect indicators of denial-of-service attacks against or launched from the system.
  11. NET-21_A11 system resources are monitored to determine if sufficient resources exist to prevent effective denial-of-service attacks.

Evidence Requirements

E-NET-04 Network Security Controls (NSC)

Documented evidence of the organization's network security controls (e.g., boundary protections, content filtering, wireless infrastructure, etc.).

Network Security

Technology Recommendations

Micro/Small

  • Enable DDoS protection on ISP/hosting provider

Small

  • Cloud-based DDoS protection (e.g., Cloudflare free tier)
  • ISP-level DDoS mitigation

Medium

  • DDoS protection service (e.g., Cloudflare, Akamai)
  • Rate limiting
  • Traffic scrubbing

Large

  • Enterprise DDoS protection (e.g., Cloudflare Enterprise, Akamai Prolexic)
  • On-premises mitigation appliances

Enterprise

  • Enterprise DDoS mitigation platform
  • BGP-based scrubbing centers
  • Always-on cloud DDoS protection
  • On-prem + cloud hybrid protection

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