CWE-1245: Improper Finite State Machines (FSMs) in… | Glexia
CWE-1245 (Improper Finite State Machines (FSMs) in Hardware Logic) weakness overview with consequences, detection methods, mitigations, related CVEs and MITRE…
Glexia's Take · Automated analysis
CWE-1245: Improper Finite State Machines (FSMs) in Hardware Logic
Improper Finite State Machines (FSMs) in Hardware Logic represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.
Executive Impact
- Availability Access Control: Unexpected State DoS: Crash, Exit, or Restart DoS: Instability Gain Privileges or Assume Identity: Faulty FSM designs that do not account for all states, either through undefined states (left as don't cares) or through incorrect implementation, might lead an attacker to drive the system into an unstable state from which the system cannot recover without a reset, thus causing a DoS. Depending on what the FSM is used for, an attacker might also gain additional privileges to launch further attacks and compromise the security guarantees.
Developer Pattern
CWE-1245 is the kind of defect developers can usually prevent with explicit validation, safer framework defaults, and tests that exercise hostile input or unsafe state transitions.
Automation confidence
high confidence from CWE-1245, 4.20.
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Official CWE Definition
CWE-1245: Improper Finite State Machines (FSMs) in Hardware Logic
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.
Developer And Remediation Guidance
How teams prevent and detect this weakness
Causes
- 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.
Remediation
- Architecture and Design Implementation: Define all possible states and handle all unused states through default statements. Ensure that system defaults to a secure state.
Detection
- Code review
- SAST
- DAST
- Focused regression tests
Mappings
Related CVEs, CWEs, and ATT&CK context
ATT&CK Relevance
ATT&CK relevance is shown only when reviewed or responsibly inferred.