CVE-2026-34446: ONNX: Arbitrary File Read via ExternalData Hardlink Bypass in ONNX load

Summary The issue is in onnx.load — the code checks for symlinks to prevent path traversal, but completely misses hardlinks, which is the problem, since a hardlink looks exactly like a regular file on the filesystem.

The Real Problem The validator in onnx/checker.cc only calls issymlink() and never checks the inode or stnlink, so a hardlink walks right through every security check without any issues.

Impact Especially dangerous in AI supply chain scenarios like HuggingFace — a single malicious model is enough to silently steal secrets from the victim's machine without them noticing anything.