# MAL-2026-5318: Malicious code in langchain-core-mcp (PyPI)


- **Type:** Malicious package
- **Package:** `langchain-core-mcp` (PyPI)
- **Published:** 6 Jun 2026
- **Also known as:** PYSEC-2026-1070

## What is MAL-2026-5318?

MAL-2026-5318 is a malicious package in langchain-core-mcp, published on 6 Jun 2026. 

### Official description

Package `langchain-core-mcp` impersonates the legitimate `langchain-core` publisher: METADATA sets Project-URL Repository to https://github.com/langchain-ai/langchain and reproduces the upstream README/description verbatim. On install, the package drops two.pth files at the site-packages root — `langchain_core-setup.pth` (notably using the legitimate package's name) and `langchain_core_mcp-setup.pth` — both of which Python auto-loads on every interpreter start. The.pth payload is obfuscated into a single line using single-letter aliases (`_O`, `_T`, `_u`, `_s`, `_b`, `_j`, `_z`,...) and wrapped in `exec('...')` to evade simple grep-based scanners. When executed, the code creates a sentinel at `/tmp/.bun_ran`, downloads the Bun runtime ZIP from `https://github.com/oven-sh/bun/releases/download/bun-v1.3.13/bun-{platform}-{arch}.zip` via `urllib.request.urlretrieve` to `/tmp/b/bun`, extracts and chmods +x, then spawns `bun run _index.js` in the background against the bundled 5.35 MB `langchain_core_mcp/_index.js` payload. The use of an alien JS runtime (Bun) to execute an opaque bundled payload bypasses Python-only inspection; auto-execution via.pth bypasses pip build isolation and fires on every Python interpreter launch on the installer's machine, not just on import of this package.

Versions 1.4.2, 1.4.3 were compromised.

Compromised packages start an obfuscated infostealer. The infostealer is a heavily obfuscated JavaScript code executed using Bun runtime on Python startup. It collectes all kinds of sensitive data, including API keys, credentials to package repositories, cryptocurrency assets, password manager data. Infostealer actively queries online services to collect additional secrets as well as attempts to gain persistence and spread further by publishing infected packages using collected credentials. Data are exfiltrated likely using Github. The code seems to threaten to wipe the user's data if it detects invalid GitHub tokens. Cleanup should be done with caution.

It seems to be related to the recent Mini Shai Hulud campaign.

---

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

Campaign: 2026-06-compr-woodpecker

Reasons (based on the campaign):

 - compromised-package

 - exfiltration-env-variables

 - exfiltration-cloud-tokens

 - exfiltration-credentials

 - abuses-pth

 - obfuscation

 - infostealer

 - The package contains code to detect if it is running in a sandbox environment.

 - exfiltration-crypto

 - files-exfiltration

 - destructive-actions

## What should I do about MAL-2026-5318?

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-2026-5318 is a malicious package: langchain-core-mcp (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-2026-5318/ (Markdown: https://insights.sbomify.com/MAL-2026-5318/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/MAL-2026-5318

---
From sbomify Insights: https://insights.sbomify.com/MAL-2026-5318/
Summaries are generated and may contain mistakes; the official description above is the record.