# MAL-2026-4592: Malicious code in jsontoken-extend (npm)


- **Type:** Malicious package
- **Package:** `jsontoken-extend` (npm)
- **Published:** 25 May 2026
- **Also known as:** GHSA-v985-2jx7-c35g

## What is MAL-2026-4592?

MAL-2026-4592 is a malicious package in jsontoken-extend, published on 25 May 2026. 

### Official description

On require()/import of jsontoken-extend, sign.js executes a top-level IIFE that base64-decodes a hardcoded string to https://www.jsonkeeper.com/b/XAMRK, fetches the JSON body, and passes data.content directly to eval(). jsonkeeper.com is an anonymous, mutable paste service — the author can change the executed payload at any time without republishing the package, giving arbitrary remote code execution on every consumer at import time. A second base64-encoded URL (https://www.jsonkeeper.com/b/W80UP) is staged but commented out, indicating multiple prepared payloads. The package name and public API (sign/verify/decode plus JsonWebTokenError/NotBeforeError/TokenExpiredError) mirror the popular jsonwebtoken library exactly, and it even declares jsonwebtoken as a dependency to pass through legitimate-looking calls — a typosquat lure to attract developers searching for the real JWT library. Base64-wrapping the C2 URLs is a deliberate static-analysis evasion. Three independent block signals are present: import-time fetch+eval from an anonymous mutable host, typosquat naming/API mirroring with malicious payload, and obfuscated C2 URL constants.

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-2026-4592?

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-2026-4592 is a malicious package: jsontoken-extend (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-2026-4592/ (Markdown: https://insights.sbomify.com/MAL-2026-4592/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/MAL-2026-4592

---
From sbomify Insights: https://insights.sbomify.com/MAL-2026-4592/
Summaries are generated and may contain mistakes; the official description above is the record.