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ONNX Security Assurance Case
Version: 1.1
Date: June 2026
Project: ONNX (Open Neural Network Exchange)
Scope: ONNX Core (onnx/onnx) and the produced Python wheel
This document provides the security assurance case for ONNX Core, supporting the OpenSSF Best Practices Badge application.
General scope and assurances
The onnx package aims to provide memory-safe parsing of untrusted protobuf bytes. Using shape/type inference, version update utilities, and model validation is also considered memory-safe. Resource exhaustion, however, may be triggered from within these utilities and users are advised to guard against this accordingly.
Validation utilities such as onnx.checker.check_model are provided on a best-effort basis (e.g. a validated ModelProto object may contain NodeProto objects that do not adhere to the ONNX specification).
The onnx reference implementation is not yet considered safe for production use on untrusted inputs.
Threat Model
Malicious model file
The attacker supplies a malicious ONNX/protobuf file to a user who parses, validates, or runs type/shape inference or version-conversion on it.
- In scope: memory safety while parsing, type/shape inference, version conversion, and validation of untrusted model bytes.
- Out of scope: resource exhaustion (DoS) from those utilities, and the reference runtime executing untrusted models.
Supply chain
The attacker compromises a dependency, the build pipeline, or the published artifact — so that a user installing onnx (e.g. from PyPI) receives malicious code.
- In scope: integrity of the published wheels and statically compiled dependencies.
- Out of scope: compromise of a user's own machine or CI, and vulnerabilities in transitive dependencies' upstream code itself.
External data references
A malicious model references external tensor data via attacker-controlled file paths, attempting to read files outside the model's directory.
- In scope: external-data paths are validated and normalized; no resolution outside the model directory.
- Out of scope: files the user has explicitly granted the model directory access to.
Secure Design Principles (Saltzer & Schroeder)
| Principle | Application in ONNX Core |
|---|---|
| Economy of Mechanism | Protocol Buffers for serialization; validation centralized in checker.cc; minimal dependencies |
| Fail-Safe Defaults | Validation on by default; must opt out with check_model=False; unknown protobuf fields rejected |
| Complete Mediation | Every model load goes through the validation pipeline; all operator inputs are type- and shape-checked |
| Least Privilege | No elevated privileges required; no network access; file I/O restricted to explicitly specified paths |
| Separation of Privilege | External data loading requires both model reference and file system access; releases require SLSA attestation |
| Least Common Mechanism | No global mutable state; validation is stateless; each API call operates independently |
| Psychological Acceptability | Secure defaults need no configuration; clear validation error messages; type-annotated Python API |
Common Weaknesses Mitigated
| CWE | Mitigation |
|---|---|
| CWE-787/125 Out-of-bounds R/W | Modern C++ (std::vector, RAII); ASan in CI |
| CWE-20 Input Validation | Comprehensive model validation on load; protobuf schema enforcement; operator shape/type checking |
| CWE-416 Use After Free | RAII/smart pointers (unique_ptr, shared_ptr); ASan in CI; code review |
| CWE-190 Integer Overflow | Checked size arithmetic in tensor allocation; UBSan in CI |
| CWE-22 Path Traversal | External data paths validated and normalized; no auto-resolution outside model directory |
| CWE-78 Command Injection | No shell execution in ONNX Core; no system()/exec() usage; enforced by code review and static analysis |
| OWASP A06 Supply Chain | Dependabot; Sigstore signing; minimal dependency footprint; SBOM generation |
| CWE-79/89/352/434 | Not applicable — ONNX Core is not a web application or database |
Security Testing
| Method | Details |
|---|---|
| Static analysis | CodeQL (GitHub Advanced Security), Clang Static Analyzer, sonarcloud |
| Dynamic analysis | ASan, MSan, UBSan, TSan in CI build matrix |
| Fuzzing | Early stage — OSS-Fuzz harnesses (onnx/fuzz) cover the checker, model loader, text parser, shape inference, version converter, and compose; reference evaluator and external-data parsing are not yet covered. A short smoke run of these harnesses is part of this repo's CI (fuzz.yml); the full OSS-Fuzz continuous campaigns run separately and are not surfaced here |
| Dependency scanning | Dependabot, OpenSSF Scorecard |
Security Processes
Vulnerability disclosure: Reports via GitHub Security Advisories (preferred) or onnx-security@lists.lfaidata.foundation as a fallback; CVE assignment through Linux Foundation CNA. See SECURITY.md.
Code review: All changes require maintainer review; security-sensitive changes require Architecture SIG review; one approval for dependency updates; automated checks must pass before merge (CODEOWNERS).
Build & distribution: artifacts signed with Sigstore; PyPI Trusted Publishing with 2FA required for maintainers; SHA256 checksums published; actions pinned to SHA in CI.
References
- ONNX Security Policy: https://github.com/onnx/onnx/blob/main/SECURITY.md
- ONNX IR Spec: https://github.com/onnx/onnx/blob/main/docs/IR.md
- Model Checker: https://github.com/onnx/onnx/blob/main/onnx/checker.cc
- OpenSSF Best Practices: https://bestpractices.coreinfrastructure.org/
- SLSA Framework: https://slsa.dev/
- CWE Top 25: https://cwe.mitre.org/top25/
- Saltzer & Schroeder Principles: https://web.mit.edu/Saltzer/www/publications/protection/
Document Maintainer: ONNX Architecture & Infrastructure SIG Last Updated: June 2026 Review Cycle: Annual (or upon significant architectural changes)