circle-flatbuffers-index-validation-poc-DO-NOT-USE

WARNING: SECURITY RESEARCH - PROOF OF CONCEPT ONLY

This repository contains malformed/crafted Circle (FlatBuffers) model files that trigger memory-safety crashes (out-of-bounds reads) in Samsung ONE's CircleImport.cpp loader. These are passive data files, not executable code — they do nothing on their own and only cause a crash when parsed by a vulnerable version of the Circle model loader.

DO NOT load these files with a production Circle/ONE runtime outside of an isolated, disposable research environment.

Findings Summary

Reproduction

1. Build Samsung ONE's circle-mlir toolchain with AddressSanitizer enabled
2. Load each .circle file through the standard model import path (CircleImport)
3. Each file passes VerifyModelBuffer() successfully but triggers an ASan-detected out-of-bounds read at the source locations listed above

All PoC files are structurally valid FlatBuffers — they pass the FlatBuffers verifier's structural checks. The vulnerability is that the verifier does NOT validate semantic consistency:

• Tensor indices are not checked against tensors.size()
• Buffer indices are not checked against buffers.size()
• Opcode indices are not checked against operator_codes.size()

Root Cause

Samsung ONE's CircleImport.cpp uses unchecked std::vector::operator[] (or FlatBuffers Vector::Get()) to access tensors, buffers, and operator codes by their index, without verifying that the index is within bounds. The FlatBuffers verifier only ensures structural validity of the FlatBuffer fields, not that index values are valid references.

// CircleImport.cpp:855 — TENSOR INDEX OOB
auto &const_tensor = *subgraph.tensors[input_num];    // input_num from op->inputs()

// CircleImport.cpp:875 — BUFFER INDEX OOB
buffer = buffers[const_tensor.buffer]->data;           // tensor.buffer from FlatBuffer

// CircleImport.cpp:1059 — OPCODE INDEX OOB
auto func_or_error = ConvertSubgraph(..., model->operator_codes, ...);
// Inside ConvertSubgraph: opcodes[op->opcode_index] is used unchecked

Mitigation

Add bounds checks before array accesses in CircleImport.cpp:

if (input_num < 0 || input_num >= subgraph.tensors.size()) { /* error */ return; }
if (const_tensor.buffer >= buffers.size()) { /* error */ return; }
if (opcode_index >= operator_codes.size()) { /* error */ return; }

Alternatively, replace operator[] with .at() which throws std::out_of_range.

Files

• tensor_index_fuzz_poc.circle (670 bytes) — verified by libFuzzer + ASan; triggers heap-buffer-overflow at tensor index access
• buffer_opcode_manual_poc.circle (524 bytes) — manually crafted with tensor.buffer=999 and opcode_index=999
• redzone_read_poc.circle (670 bytes) — fuzz-discovered; triggers SEGV via FlatBuffers offset past buffer end
• report.md — Full vulnerability report

Credits

Discovered by Onurcan Genc via coverage-guided fuzzing with libFuzzer + ASan + UBSan.