# CoreML (apple/coremltools) MILBlob Span::Slice integer-overflow bounds-check bypass -> OOB read

PoC package for a heap/mapped out-of-bounds read in the CoreML weight-blob parser
(`MILBlob`) shipped in `apple/coremltools`. A crafted `.mlmodelc` / `weights.bin`
weight-blob file with attacker-controlled `blob_metadata.offset` and
`blob_metadata.sizeInBytes` (both `uint64`) triggers a 64-bit integer overflow in
the bounds check inside `Span<T>::Slice(index, size)`, returning a `Span` whose
`Size()` is enormous (here `2^64 - 50`). A consumer reading the weight bytes then
reads far past the mapped file.

## Files

- `weights.bin`     - the malicious CoreML weight-blob file (384 bytes)
- `craft.py`        - script that generates `weights.bin` (documents the byte layout)
- `harness.cpp`     - ASan harness that drives the REAL `StorageReader` / `MMapFileReader` / `Span`
- `build.sh`        - build command (clang++ + ASan)
- `asan_crash.txt`  - the captured AddressSanitizer crash trace

## Reproduce

    git clone --filter=blob:none --sparse https://github.com/apple/coremltools.git
    cd coremltools
    git sparse-checkout set mlmodel/src/MILBlob
    # commit pinned for this PoC: 3fb88603a6af3d12bf72ca2dcc0a3724a631317b

    clang++ -std=c++17 -fsanitize=address -g -O0 -Imlmodel/src \
      harness.cpp \
      mlmodel/src/MILBlob/Blob/StorageReader.cpp \
      mlmodel/src/MILBlob/Blob/MMapFileReader.cpp \
      mlmodel/src/MILBlob/Blob/MMapFileReaderFactory.cpp \
      -o harness

    python3 craft.py
    ASAN_OPTIONS=detect_leaks=0 ./harness weights.bin

## Root cause

`mlmodel/src/MILBlob/Util/Span.hpp` (~line 325):

    Span<T> Slice(size_t index, size_t size) const
    {
        MILVerifyIsTrue(size > 0 && index < Size() && index + size <= Size(), std::range_error, "index out of bounds");
        return Span<T>(Data() + index, size);
    }

`index + size` is an unchecked 64-bit addition. With `index = 100` and
`size = 2^64 - 50`, `index + size` wraps to `50`, which is `<= Size()`, so the
check passes and an oversized `Span` is returned.

Both operands are attacker-controlled: `StorageReader::Impl::GetRawDataView`
(`StorageReader.cpp`) calls `m_reader->ReadData(metadata.offset, metadata.sizeInBytes)`,
and `MMapFileReader::ReadData` (`MMapFileReader.cpp`) forwards straight to
`m_dataSpan.Slice(offset, length)`. The only validation on the metadata is the
`sentinel == 0xDEADBEEF` check in `GetMetadata` - `offset` and `sizeInBytes` are
never range-checked before reaching `Slice`.

## Source availability

100% open source, BSD-3-Clause: https://github.com/apple/coremltools
Vulnerable file: `mlmodel/src/MILBlob/Util/Span.hpp`.