ISO 26262 is about functional safety: hazards from malfunctioning electrical and electronic systems. ISO/SAE 21434 is about cybersecurity engineering across the vehicle life cycle. One asks what happens if a part fails. The other asks what happens if someone attacks it. A modern vehicle needs both.
What ISO 26262 covers
ISO 26262, titled Road vehicles, Functional safety, was first published in 2011 and revised in December 2018. The first edition covered passenger cars up to 3,500 kg. The second edition extended to all road vehicles except mopeds.
Its core tool is the Automotive Safety Integrity Level, from ASIL A as the lowest to ASIL D as the highest. Below that is QM, where only normal quality management applies. ASIL D corresponds to the most severe injuries, the highest exposure and the hardest to control situations. The standard adapts the industrial standard IEC 61508.
What ISO/SAE 21434 covers
Secondary summaries describe it as a cybersecurity framework for the lifecycle of road vehicles, and as the security counterpart to ISO 26262. UL says it was published in 2021 and identifies engineering requirements for a cybersecurity management system. The points here come from summaries, so check the official document before building a process on them.
Its main risk method is the threat analysis and risk assessment. Governance matters too: summaries say it expects a cybersecurity policy and visible commitment from executive management.
Key differences
| Aspect | ISO 26262 | ISO/SAE 21434 |
|---|---|---|
| Concern | Faults and malfunctions | Deliberate attacks |
| Risk scale | ASIL A to D, plus QM | Risk from threat scenarios and feasibility |
| Assumption | Failures are random or systematic | Attackers adapt |
| Typical output | Safety goals and requirements | Cybersecurity goals and controls |
Where they meet
A cyber attack can cause a safety hazard. If an attacker can alter a braking message, the safety case changes. Safety teams need to know which security assumptions their arguments depend on, and security teams need to know which functions are safety relevant, because that raises the impact rating in a threat analysis.
A sensible interface is a shared register of assets and functions. Each item carries its ASIL and its security impact, and both teams review changes to it.
How regulation ties in
UN R155 does not replace either standard. UL describes ISO/SAE 21434 as the engineering requirements for the CSMS that R155 asks for. UL's summary of R156 also says each update must be assessed for its effect on functional safety and driving safety, so the two worlds meet in update management.
A short example
Consider an electric power steering unit. The safety analysis assigns a high integrity level because failure is dangerous. The security analysis then asks how an attacker could send false steering commands, which interfaces reach the unit and how feasible each path is. The high safety impact raises the importance of that security work, so the outputs of one analysis feed the other.
Quick check
Does a high ASIL mean a function is secure?
No. ASIL measures safety integrity against faults. It says nothing about resistance to attack.
Sources
Last reviewed: 19 October 2026.
