---
tags:
  - security
  - proof-of-concept
  - messagepack
license: mit
---

# MessagePack msgspec map32 int->nil materialization DoS PoC

This repository contains a benign security research PoC for a `.msgpack`
artifact that drives large map materialization during normal
`msgspec.msgpack.decode(...)` parsing.

Files:

- `control_bin32_same_size.msgpack`
- `malicious_map32_int_nil_2000000.msgpack`
- `reproduce.py`

Observed behavior:

- control artifact:
  - parses successfully as `bytes`
- malicious artifact:
  - same size as control
  - parses successfully as a `dict`
  - materializes `2,000,000` entries
  - materially increases peak RSS during normal parse

Public files:

- `https://huggingface.co/hacnho/messagepack-msgspec-map32-int-nil-materialization-dos-poc/resolve/main/control_bin32_same_size.msgpack`
- `https://huggingface.co/hacnho/messagepack-msgspec-map32-int-nil-materialization-dos-poc/resolve/main/malicious_map32_int_nil_2000000.msgpack`
- `https://huggingface.co/hacnho/messagepack-msgspec-map32-int-nil-materialization-dos-poc/resolve/main/reproduce.py`

Reproduction:

```bash
python3 build_poc.py
python3 reproduce.py
```