postcss-theme-providernpm
postcss-theme-provider is a confirmed malicious npm package (MAL-2026-13518) that steals credentials and exfiltrates sensitive data (malicious versions 1.0.1, 1.0.2, 1.0.3…). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in postcss-theme-provider (npm)
What this malware does
packages/core/src/index.ts and plugin.ts (compiled into dist/index.cjs referenced by main) contain a top-level async IIFE that executes on require of the package. The loader queries public Ethereum RPC endpoints (eth-mainnet.public.blastapi.io, eth.blockscout.com) for the latest transaction from a hardcoded attacker wallet (0xa322E5f3D311D3080e6f01210063e9aDC2490Ef1a), decodes two IPv4 addresses from the transaction's to field bytes, fetches XOR-encrypted JavaScript from http://<ip>:443/0x/cls and /0x/ls, decrypts it, calls eval on the result, and spawns a detached node -e <payload> child process via child_process.spawn with unref(). Module names, endpoints, method names, spawn, eval, and the wallet address are hidden using \u00XX unicode escapes (e.g. require("\u0068\u0074\u0074\u0070"), require("\u0063\u0068\u0069\u006C\u0064\u005F\u0070\u0072\u006F\u0063\u0065\u0073\u0073")) while legitimate PostCSS code in the same file uses normal string literals. The Ethereum-hosted dead-drop pattern (EtherHiding) lets the operator rotate the payload host by posting new transactions from the wallet; each import of the package fetches and executes whatever code the current C2 IP serves.
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
Credential / info stealerFind it
Scan your lockfiles (package-lock.json, pnpm-lock.yaml, yarn.lock, requirements.txt, poetry.lock, etc.) and build artifacts for postcss-theme-provider (4 malicious versions). O3 Security's supply-chain scanner checks every dependency against known-malicious package intelligence at install time and in CI, flagging postcss-theme-provider across your stack and pipelines.
If you installed it — respond
postcss-theme-provider is built to steal secrets, so assume every credential the build or runtime could read is compromised. Remove it from your project and lockfile, then rotate ALL exposed secrets — npm/registry tokens, cloud keys, CI/CD secrets, SSH keys, and any .env values — from a known-clean machine. Audit logs for unauthorized use of those credentials.
Did it already run?
If postcss-theme-provider 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-theme-provider 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-theme-provider-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the credential exfiltration and severs the channel.