---
license: apache-2.0
tags: [security-research, huntr, model-file-security, scanner-bypass]
---

# picklescan & ModelScan bypass: LONG-opcode parser desync (read_decimalnl_long base-10 vs C base-0)

**Benign security-research PoC** for the huntr Model File Format program. The payload only writes a nonce marker file (`echo` / `io.open`) — no real harm, no network, no secrets (huntr §benign).

## Vulnerability
The L (LONG) opcode's newline-terminated int is parsed base-10 by pickletools.read_decimalnl_long but base-0 by the C unpickler. `L0x10L\n` makes both scanners' genops walk raise+abort before the payload, while pickle/torch.load run it. Distinct opcode + distinct reader from the INT-opcode (int-desync) variant.

## Measured evidence (2026-07-24)
Against picklescan 1.0.5 + ModelScan 0.8.8: both fail to flag; on load the benign marker fires. Re-verify: `python -m nomos_redteam scanbypass`.

## Reproduce
```python
import torch  # or: import pickle
obj = torch.load("model.pt", weights_only=False)   # fires the benign marker at load
```
Scan first to confirm the bypass:
```bash
picklescan -p model.pt      # exit 0 / no dangerous global
modelscan -p model.pt        # no issue reported
```