# MAL-2026-15603: Malicious code in pyservercheck (PyPI)


- **Type:** Malicious package
- **Package:** `pyservercheck` (PyPI)
- **Published:** 31 Aug 2026

## What is MAL-2026-15603?

MAL-2026-15603 is a malicious package in pyservercheck, published on 31 Aug 2026. 

### Official description

The package ships a bundled Node script pyservercheck/js/main.js whose visible top half is a healthcheck stub matching the README, followed by a long run of tab whitespace and a trailing eval(atob('...')) that decodes to a two-stage loader. The decoded loader queries public Ethereum RPC endpoints (eth.blockscout.com, 1rpc.io/eth, eth.drpc.org, ethereum-rpc.publicnode.com, eth-mainnet.public.blastapi.io) for the latest transaction from the hardcoded sender 0xa322E5f3D311D3080e6f0121063e9aDC2490Ef1a, extracts an IPv4 pair from the tx `to` field, fetches XOR-obfuscated stage-2 code from http://<decoded-ip>:443/0x/cls and /0x/ls, eval()s it, and re-launches it via a detached `spawn('node', ['-e', <code>])`. Execution is wired to two auto-triggers: pyproject.toml overrides setuptools `build_py` and `develop` with pyservercheck._setup_cmd.BuildPy/Develop, whose `run()` calls _run_main_js_now() -> subprocess.run(['node', main.js]) during `pip install` / `pip install -e.`; and BuildPy also writes a `pyservercheck.pth` file containing `import pyservercheck._hooks; pyservercheck._hooks.ensure_once()`, which Python auto-executes at every interpreter startup, invoking run_js() again. The `.main_js_ran` marker is advisory and can be removed to force re-execution. The C2 destination is rotatable by publishing a new Ethereum transaction from the sender address, so the fetched payload is fully attacker-controlled at each run.

Package embeds obfuscated, JS-based malware downloading further remote stages. The code is triggered during building the package and on every Python startup (via PTH file). The next-stage IP is delivered via a blockchain. 

The payload and embedded IoCs are consistent with campaigns attributed to Lazarus APT/PolinRider.

---

Category: MALICIOUS - The campaign has clearly malicious intent, like infostealers.

Campaign: 2026-08-pybitjs

Reasons (based on the campaign):

 - obfuscation

 - Downloads and executes a remote malicious script.

 - malware

 - abuses-pth

 - c2-in-blockchain

## What should I do about MAL-2026-15603?

Remove the package from your dependencies and lockfiles, then rotate any secrets on machines where it was installed.

## Fix prompt for AI coding agents

```text
MAL-2026-15603 is a malicious package: pyservercheck (PyPI). Every version was published to cause harm.

Task:
1. Search this repository's dependency manifests and lockfiles for the package, including transitive dependencies.
2. If it is present, remove it, regenerate the lockfile with the project's package manager, and replace whatever it was used for.
3. List any CI runners, developer machines or containers that installed it, so their secrets can be rotated.
4. If the package is not used anywhere, say so and change nothing.

Reference: https://insights.sbomify.com/MAL-2026-15603/ (Markdown: https://insights.sbomify.com/MAL-2026-15603/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/MAL-2026-15603

---
From sbomify Insights: https://insights.sbomify.com/MAL-2026-15603/
Summaries are generated and may contain mistakes; the official description above is the record.