xiaoyaoes/cntk-model-rce-poc

CNTK v2 (.model) — UserFunction Deserialization exec() RCE

MFV Target: CNTK v2 ($1500) Format: .model (CNTKv2 binary format)

Vulnerability

cntk/internal/__init__.py, line 54:

exec("from {} import {}".format(module, cls))

The CNTK deserialization callback _UDFDeserializeCallbackWrapper.__call__() calls exec() with attacker-controlled module and class values extracted directly from the UserFunction dictionary in a .model binary file. No sanitization is performed.

Impact

• CVSS 9.8 (Critical)
• Remote code execution via model loading
• No authentication required
• Full system compromise (C/I/A all HIGH)

Attack Chain

1. Craft .model file with module="os", class="system" in UserFunction serialized dict
2. Upload to HuggingFace
3. ModelScan skips .model files entirely — zero coverage
4. Victim: cntk.load_model("malicious.model")
5. C++ deserializer → Python callback → exec("from os import system") → RCE

PoC Files

• exploit.py — Python-level PoC demonstrating the exact code path
• REPORT.md — Full MFV submission report (8 sections)

ModelScan Status

ModelScan 0.8.8 does NOT support .model (CNTK) at all. The extension is absent from all scanner configuration lists.

Note

The full end-to-end exploit requires the CNTK C++ extension (_cntk_py.so) with libmpi to construct a binary .model file. The Python-level code path in the callback is identical to the production code.