koboldcpp-legacy-ndims-stack-oob-poc

PoC — koboldcpp legacy ggml loaders: unchecked n_dims → ne[2] stack buffer overflow

huntr MFV PoC vs LostRuins/koboldcpp otherarch/*. Authorized security research (responsible disclosure via huntr).

koboldcpp's legacy ggml loaders read a per-tensor int32_t n_dims from the model file and loop for (i=0;i<n_dims;++i) fin.read(&ne[i], ...) into a fixed int32_t ne[2] — with no n_dims<=2 check. n_dims>=3 writes attacker-controlled bytes past the 2-element stack array (CWE-787). Present in gpt2_v1/ v2/v3, gptj_v1/v2/v3, mpt_v3, llama_v2/v3, neox_v2/v3, rwkv_v2 (reached via FileFormat detection).

Files

• ndims_repro.cpp / CRASH_PROVEN.md — isolated repro; EXC_BAD_ACCESS at the ne[i] store.

Reproduce

c++ -O0 -g -fstack-protector-all ndims_repro.cpp -o ndims_repro && ./ndims_repro 100000   # -> SIGSEGV

Fix

Add if (n_dims < 0 || n_dims > 2) return ModelLoadResult::FAIL; before the ne-fill loop in each loader.