Because they are the external surfaces that translate identity into physical control. When those services can change permissions or issue vehicle commands, any weakness in registration, authorisation, or monitoring can have real-world impact. Teams need to treat those APIs as privileged services, not as simple mobile integrations.
Why This Matters for Security Teams
Companion apps and backend APIs are the control plane for modern vehicles. They sit outside the car but can still unlock doors, start engines, locate vehicles, change settings, and manage who is allowed to do those things. That makes them far more sensitive than a normal mobile backend. The risk is not only data exposure, but unauthorized physical action.
Security teams often underestimate this boundary because the app looks consumer-facing while the API looks like routine service plumbing. In practice, those services usually hold the trust relationships that connect a user account, a device, a vehicle, and sometimes a dealer or fleet operator. That is why NIST Cybersecurity Framework 2.0 is useful here: it forces attention on governance, protection, detection, and recovery across the full service chain, not just the app layer.
In practice, many security teams encounter abuse of companion-app trust only after an account takeover, token leak, or API flaw has already translated into vehicle access.
How It Works in Practice
The risk comes from how identity and privilege are implemented across multiple systems. A companion app usually authenticates the human user, but the backend must also verify device trust, session integrity, API scope, vehicle ownership, and command authorization before any action reaches the car. If any one of those checks is weak, attackers may replay tokens, bypass object-level authorization, or chain logic flaws into privileged vehicle commands.
Good designs treat the API as a privileged service and use layered controls. That includes strong authentication, short-lived tokens, command-level authorization, tamper-resistant logging, rate limiting, and step-up verification for sensitive actions. Security monitoring should focus on unusual command patterns, impossible travel, token abuse, and changes in ownership or delegation. For implementation detail, NIST SP 800-53 Rev 5 Security and Privacy Controls is a solid reference for access control, audit logging, configuration management, and incident response expectations.
- Authenticate the user, the device, and the session separately.
- Enforce object-level checks so a valid login cannot control another vehicle.
- Require explicit authorization for high-risk actions such as unlock, start, or share access.
- Log command origin, identity context, and vehicle response for detection and investigation.
- Test the API for broken access control, replay, and abuse of delegated permissions.
This model works best when vehicle commands are exposed through a narrow, well-governed API layer. These controls tend to break down when multiple mobile apps, dealer portals, fleet tools, and legacy telematics services share the same backend identity model because trust boundaries become ambiguous.
Common Variations and Edge Cases
Tighter command authorization often increases friction for legitimate users, requiring organisations to balance usability against theft resistance and account recovery speed.
There is no universal standard for every connected-car deployment yet, so best practice is evolving. Consumer vehicles, fleet platforms, rental services, and dealer ecosystems all create different trust boundaries. A fleet console may legitimately need broad administrative control, while a consumer app should be tightly scoped and heavily monitored. Shared accounts, household access, valet modes, temporary delegation, and offline vehicle states all complicate the security model.
The identity bridge matters here. When a companion app uses weak registration, poor recovery flows, or reused credentials, the resulting compromise can affect not just digital access but a physical asset. For carmakers operating across regions, privacy, safety, and regulatory obligations may also overlap with incident reporting and secure software lifecycle expectations. Current guidance suggests designing for least privilege, continuous verification, and strong ownership proof rather than assuming a logged-in app session is enough.
Edge cases also appear when APIs are reused by third parties. If a partner platform can call the same command endpoints as the official app, scope separation and contractual control become part of the security model. The safest pattern is to treat each integration as a distinct trust domain, with explicit approval paths and revocation capability.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
OWASP Non-Human Identity Top 10 address the attack and risk surface, while NIST CSF 2.0 and NIST AI RMF set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| NIST CSF 2.0 | PR.AC-4 | Connected-car APIs need strict access control for command authorization. |
| NIST AI RMF | Identity and privilege decisions should be governed as a managed risk process. | |
| OWASP Non-Human Identity Top 10 | NHI-1 | Backend APIs often fail when non-human or service identities are over-privileged. |
Inventory service identities, reduce standing privilege, and rotate credentials tied to vehicle actions.
Related resources from NHI Mgmt Group
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Reviewed and updated by the NHIMG editorial team on July 14, 2026.
NHI Mgmt Group — the #1 independent authority on Non-Human Identity, IAM, and Agentic AI security. nhimg.org
