CWE-1245: Improper Finite State Machines (FSMs) in Hardware Logic

Code Examples & CVEs

Demonstrative Examples

The Finite State Machine (FSM) shown in the "bad" code snippet below assigns the output ("out") based on the value of state, which is determined based on the user provided input ("user_input").

The case statement does not include a default to handle the scenario when the user provides inputs of 3'h6 and 3'h7. Those inputs push the system to an undefined state and might cause a crash (denial of service) or any other unanticipated outcome. Adding a default statement to handle undefined inputs mitigates this issue. This is shown in the "Good" code snippet below. The default statement is in bold.

BadVerilog

module fsm_1(out, user_input, clk, rst_n); 					  input [2:0] user_input;  					  input clk, rst_n; 					  output reg [2:0] out; 					  reg [1:0] state; 					  always @ (posedge clk or negedge rst_n ) 					   					  begin 					   					   						if (!rst_n) 						 						  state = 3'h0; 						 						else 						case (user_input) 						 						  3'h0: 						  3'h1: 						  3'h2: 						  3'h3: state = 2'h3; 						  3'h4: state = 2'h2; 						  3'h5: state = 2'h1; 						 						endcase 					   					  end 					  out <= {1'h1, state}; 					   					  endmodule

The Finite State Machine (FSM) shown in the "bad" code snippet below assigns the output ("out") based on the value of state, which is determined based on the user provided input ("user_input").

GoodVerilog

case (user_input) 					  3'h0: 					  3'h1: 					  3'h2: 					  3'h3: state = 2'h3; 					  3'h4: state = 2'h2; 					  3'h5: state = 2'h1; 					  default: state = 2'h0; 					 					  endcase

Source-backed guidance

Additional facts reviewed against primary or authoritative security sources.

Verify controls for CWE-1245 with SSDF evidence

Use NIST SSDF verification and vulnerability-response practices to detect CWE-1245, Improper Finite State Machines (FSMs) in Hardware Logic, throughout the product lifecycle. Derive review questions, static or dynamic checks, and negative tests from the CWE's causal behavior; define the components and lifecycle stages each check covers; and retain findings with enough evidence to distinguish the root cause from symptoms and impacts. Track escapes and false negatives, then improve the verification plan after every confirmed occurrence.

NIST SP 800-218 Secure Software Development Framework — National Institute of Standards and Technology

Address Improper Finite State Machines (FSMs) in Hardware Logic during Architecture and Design

MITRE associates mitigation with Architecture and Design, and Implementation; recorded impacts include Unexpected State, DoS: Crash, Exit, or Restart, DoS: Instability, and Gain Privileges or Assume Identity; the entry maps to CAPEC-74. Use these source-defined anchors to turn CWE-1245 into implementation, review, and verification checks for the affected component.

CWE-1245: Improper Finite State Machines (FSMs) in Hardware Logic — MITRE CWE

Triage CWE-1245 against known exploitation evidence

Use CISA's Known Exploited Vulnerabilities catalog to test whether a vulnerability mapped to CWE-1245, Improper Finite State Machines (FSMs) in Hardware Logic, has evidence of exploitation in the wild. Confirm the CVE-to-CWE root-cause mapping independently before attaching the example, then capture the affected product, required action, and remediation deadline. A missing KEV match is not evidence that the weakness is unexploited, and a KEV entry must not be generalized to every occurrence of this CWE.

Known Exploited Vulnerabilities Catalog — Cybersecurity and Infrastructure Security Agency

Apply precise root-cause mapping to CWE-1245

Apply MITRE's full root-cause mapping guidance when using CWE-1245, Improper Finite State Machines (FSMs) in Hardware Logic. Separate weakness language from attacker prerequisites and technical impact, check the entry's abstraction and vulnerability-mapping notes, and prefer the most specific Base or Variant supported by the evidence. Record the rejected alternatives and require an independent review before the mapping is used for remediation trends or program metrics.

CVE to CWE Root Cause Mapping Guidance — MITRE CWE

Validate CWE-1245 with root-cause mapping checks

Apply MITRE's root-cause mapping quick tips to CWE-1245, Improper Finite State Machines (FSMs) in Hardware Logic. Confirm the finding describes the causal weakness rather than an impact or attack pattern, compare the abstraction and mapping notes with plausible alternatives, and have a second reviewer challenge the selection. Preserve the evidence and reasoning so recurring defects can be measured against one consistent identifier.

CVE to CWE Root Cause Mapping Quick Tips — MITRE CWE

Frequently Asked Questions

What is CWE-1245: Improper Finite State Machines (FSMs) in Hardware Logic?+

CWE-1245: Improper Finite State Machines (FSMs) in Hardware Logic is a Common Weakness Enumeration (CWE) entry maintained by MITRE. Faulty finite state machines (FSMs) in the hardware logic allow an attacker to put the system in an undefined state, to cause a denial of service (DoS) or gain privileges on the victim's system. The functionality and security of the system heavily depend on the implementation of FSMs. FSMs can be used to indicate the current security state of the system. Lots of secure data operations and data transfers rely on the state reported by the FSM.

What are the security consequences of Improper Finite State Machines (FSMs) in Hardware Logic?+

If exploited, CWE-1245 (Improper Finite State Machines (FSMs) in Hardware Logic) it can compromise Availability and Access Control, leading to outcomes such as Unexpected State, DoS: Crash, Exit, or Restart, DoS: Instability and Gain Privileges or Assume Identity.

How do you prevent or mitigate Improper Finite State Machines (FSMs) in Hardware Logic?+

Recommended mitigations for CWE-1245 include: Define all possible states and handle all unused states through default statements. Ensure that system defaults to a secure state.

Which programming languages are affected by Improper Finite State Machines (FSMs) in Hardware Logic?+

CWE-1245 commonly affects Not Language-Specific. Note that weaknesses are often language-agnostic patterns, so secure coding practices apply broadly.

What is the difference between a CWE and a CVE?+

A CWE (Common Weakness Enumeration) like CWE-1245 describes a category of software weakness — the underlying flaw type. A CVE (Common Vulnerabilities and Exposures) identifies a specific, real-world vulnerability in a particular product. In short, a CWE is the kind of mistake, and a CVE is an instance of that mistake being found in software.

CWE-1245: Improper Finite State Machines (FSMs) in Hardware Logic

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