postcss-minify-selector-parsernpm
postcss-minify-selector-parser is a confirmed malicious npm package (MAL-2026-5737) that typosquats a legitimate package to trick installs (malicious versions 1.0.11, 1.0.12, 1.0.13…). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in postcss-minify-selector-parser (npm)
What this malware does
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.
Malicious versions
Indicators of compromise (SHA-256)
Detection & response playbook
TyposquatFind it
Scan your lockfiles (package-lock.json, pnpm-lock.yaml, yarn.lock, requirements.txt, poetry.lock, etc.) and build artifacts for postcss-minify-selector-parser (9 malicious versions). O3 Security's supply-chain scanner checks every dependency against known-malicious package intelligence at install time and in CI, flagging postcss-minify-selector-parser across your stack and pipelines.
If you installed it — respond
postcss-minify-selector-parser is a typosquat — you almost certainly intended a legitimately-named package. Remove postcss-minify-selector-parser, install the correct package, and rotate any secrets exposed during the install since post-install scripts may have already run.
Did it already run?
If postcss-minify-selector-parser was ever installed, its post-install/runtime payload may have already executed. O3's L7 egress monitoring and runtime eBPF sensors detect the credential exfiltration or command-and-control callback after install and block the malicious outbound channel, so you catch and contain the actual compromise — not just the presence of the package.
How O3 protects you
O3 blocks postcss-minify-selector-parser before install through its supply-chain scanner, and if it has already run, detects and severs the exfiltration or C2 callback at runtime through L7 egress monitoring and eBPF.
Frequently asked questions
Campaign
References
Credits
- Amazon Inspector · finder
Detect & block this
O3 blocks postcss-minify-selector-parser-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the malicious outbound activity and severs the channel.