GitHub Security Advisory: GHSA-j842-xgm4-wf88
Package: mlx (PIP)
Severity: MODERATE (CVSS 0.0)
CWE: CWE-476: NULL Pointer Dereference
Vulnerable versions: <= 0.29.3
Patched in: 0.29.4

Summary: MLX has Wild Pointer Dereference in load_gguf()

Details:
## Summary

Segmentation fault in `mlx::core::load_gguf()` when loading malicious GGUF files. Untrusted pointer from external gguflib library is dereferenced without validation, causing application crash.

Environment:
- OS: Ubuntu 20.04.6 LTS
- Compiler: Clang 19.1.7

## Vulnerability

**Location**: `mlx/io/gguf.cpp`
- Function `extract_tensor_data()` at lines 59-79
- Vulnerable memcpy at lines 64-67
- Called from `load_arrays()` at line 177

**The Bug**:
```cpp
std::tuple<allocator::Buffer, Dtype> extract_tensor_data(gguf_tensor* tensor) {
  std::optional<Dtype> equivalent_dtype = gguf_type_to_dtype(tensor->type);
  if (equivalent_dtype.has_value()) {
    allocator::Buffer buffer = allocator::malloc(tensor->bsize);
    memcpy(
        buffer.raw_ptr(),
        tensor->weights_data,  // untrusted pointer from gguflib
        tensor->num_weights * equivalent_dtype.value().size());
    return {buffer, equivalent_dtype.value()};
  }
  // ...
}
```

## Possible Fix

```cpp
std::tuple<allocator::Buffer, Dtype> extract_tensor_data(gguf_tensor* tensor) {
  std::optional<Dtype> equivalent_dtype = gguf_type_to_dtype(tensor->type);
  if (equivalent_dtype.has_value()) {
    // FIX: Validate pointer
    if (!tensor->weights_data) {
      throw std::runtime_error("[load_gguf] NULL tensor data pointer");
    }

    allocator::Buffer buffer = allocator::malloc(tensor->bsize);
    memcpy(
        buffer.raw_ptr(),
        tensor->weights_data,
        tensor->num_weights * equivalent_dtype.value().size());
    return {buffer, equivalent_dtype.value()};
  }
  // ...
}
```

## PoC

```bash
# Install MLX
pip install mlx

python3 -c "import mlx.core as mx; mx.load('exploit.gguf', format='gguf')"
```

Download the poc file [there](https://drive.google.com/file/d/1t9Z2RJGn-oHmluKWebU077UWSMGXeuVp/view?usp=sharing), or let me know how I can send it to you.

**AddressSanitizer Output (with instrumented build)**:
```
AddressSanitizer:DEADLYSIGNAL
=================================================================
==5855==ERROR: AddressSanitizer: SEGV on unknown address 0x7fc432f64bc0 (pc 0x7fc430841c12 bp 0x7ffc04847ab0 sp 0x7ffc04847268 T0)
==5855==The signal is caused by a READ memory access.
    #0 0x7fc430841c12  /build/glibc-B3wQXB/glibc-2.31/string/../sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S:312
    #1 0x55aac829756b in __asan_memcpy (/home/user1/mlx/fuzz/load_gguf/fuzz_load_gguf+0x9ef56b) (BuildId: 57467f1ce96052757daeef4b04739be7f23c5f1f)
    #2 0x55aacaa6e8dc in mlx::core::extract_tensor_data(gguf_tensor*) /home/user1/mlx/mlx/io/gguf.cpp:64:5
    #3 0x55aacaa773fc in mlx::core::load_arrays[abi:cxx11](gguf_ctx*) /home/user1/mlx/mlx/io/gguf.cpp:226:35
    #4 0x55aacaa782a9 in mlx::core::load_gguf(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char>> const&, std::variant<std::monostate, mlx::core::Stream, mlx::core::Device>) /home/user1/mlx/mlx/io/gguf.cpp:250:17
    #5 0x55aac82dc696 in LLVMFuzzerTestOneInput /home/user1/mlx/fu