# MAL-2026-5737: Malicious code in postcss-minify-selector-parser (npm)


- **Type:** Malicious package
- **Package:** `postcss-minify-selector-parser` (npm)
- **Published:** 13 Jun 2026
- **Also known as:** GHSA-3m8w-m4vc-8f58

## What is MAL-2026-5737?

MAL-2026-5737 is a malicious package in postcss-minify-selector-parser, published on 13 Jun 2026. 

### Official description

The package name impersonates the widely-used postcss-selector-parser library (which it also declares as a dependency and re-exports verbatim from src/selector-parser.js, providing cover for installers who mistype the real package). On top of that legitimate re-export, the package ships a sealed AES-GCM ciphertext as DEFAULT_FINAL_ENCODED_TEXT in src/config/defaults.js together with a hardcoded passphrase (`default-dev-passphrase`) and salt. src/pipeline/custom-codec-pipeline.js line 53 decrypts the blob and evaluates the cleartext via `new Function("require", runnable)(require)`, handing the decrypted code full `require` capability on the installer's machine. This decode-and-eval path is reachable through the package's exported `run` / `decodeAndRunPlain` / `runDefaultDecodedFunction` API, through `require('postcss-minify-selector-parser/cjs-runner')`, and through the bundled `runtime/lib.min.js` and `scripts/cjs-runner.js`. The README documents none of this — it presents the package as a CSS selector parser. The combination of typosquat name, hidden encrypted payload, multi-layer custom codec pipeline (position-unit-codec + encode-decode-codec + AES-GCM) used solely to wrap that payload, and direct `new Function(require)` execution of the decrypted bytes is the canonical opaque-blob-eval supply-chain attack shape. Author field is empty, no repository URL is declared, license is generic ISC.

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-2026-5737?

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-2026-5737 is a malicious package: postcss-minify-selector-parser (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-2026-5737/ (Markdown: https://insights.sbomify.com/MAL-2026-5737/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/MAL-2026-5737

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From sbomify Insights: https://insights.sbomify.com/MAL-2026-5737/
Summaries are generated and may contain mistakes; the official description above is the record.