# MAL-2026-6205: Malicious code in ts-esys (npm)


- **Type:** Malicious package
- **Package:** `ts-esys` (npm)
- **Published:** 19 Jun 2026
- **Also known as:** GHSA-76f5-jq4m-cjc3

## What is MAL-2026-6205?

MAL-2026-6205 is a malicious package in ts-esys, published on 19 Jun 2026. 

### Official description

The package is published as `ts-esys` but its package.json author, repository URL, funding metadata, and README are copied verbatim from MikeMcl/big.js (which advertises 'No dependencies'). Both entrypoints `big.js` and `big.mjs` contain a top-level `try { const doc = require('websocket-slot'); doc.from_str().then(...).catch(...) } catch {}` block that runs on every `require('ts-esys')` / `import` of either entrypoint. The dependency `websocket-slot ^0.0.6` is unrelated to the advertised arbitrary-precision-decimal purpose, is not mentioned in the README (which still claims 'No dependencies'), and any error from its execution is silently swallowed. The combination of identity impersonation + hidden runtime dependency loader + concealed errors is the standard supply-chain launcher pattern: installers who pull `ts-esys` (e.g., expecting big.js-compatible behavior) execute whatever code `websocket-slot` ships, with no surface visibility.

Any computer that has this package installed or running should be considered fully compromised. All secrets and keys stored on that computer should be rotated immediately from a different computer. The package should be removed, but as full control of the computer may have been given to an outside entity, there is no guarantee that removing the package will remove all malicious software resulting from installing it.

## What should I do about MAL-2026-6205?

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-2026-6205 is a malicious package: ts-esys (npm). 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-2026-6205/ (Markdown: https://insights.sbomify.com/MAL-2026-6205/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/MAL-2026-6205

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From sbomify Insights: https://insights.sbomify.com/MAL-2026-6205/
Summaries are generated and may contain mistakes; the official description above is the record.