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Malicious package

css-at-scope-polyfillnpm

Advisory published Updated

css-at-scope-polyfill is a confirmed malicious npm package (MAL-2026-17547) that opens a backdoor for remote access (malicious version 1.0.0). Do not install it — remove it immediately and rotate any exposed credentials.

Malicious code in css-at-scope-polyfill (npm)

MAL-2026-17547
Immediate action
Remove the package, then rotate any secrets the build/runtime could reach.
npm uninstall css-at-scope-polyfill

What this malware does

Package is published under a CSS-polyfill name but ships thunderboltRegistry.js, which exports Wix internal registry module names (thunderboltRegistry, siteAssetsRegistry, editorRegistry, corvidRegistry, etc.) so that a build resolving any of those names will load this file. On require(), an IIFE runs child_process.execSync to collect id, whoami, uname, ifconfig/ip addr, and the contents of /etc/hosts, plus a beacon containing node version, platform, pid, and hostname, and POSTs the output via fetch to the hardcoded HTTP endpoint http://dxpoc.gt.tc/callback.php/bb8968d0f67000433bf7005dd5ad2d1f. The payload clears any require.cache entries referencing 'thunderboltRegistry' and acquires child_process through three fallbacks, including instantiating a new Module via module.constructor to bypass mocks or sandboxes. The declared CSS-polyfill purpose has no relation to this behavior; the shape is a dependency-confusion squat against internal Wix modules.

Malicious versions

1 flagged
1.0.0

Indicators of compromise (SHA-256)

c4d8d974b7fabf04fa662971cd8041fb76775bf5ed2902cbbffed0f881e2036d

Detection & response playbook

Backdoor / remote access

  1. Find it

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

  2. If you installed it — respond

    css-at-scope-polyfill establishes remote access, so treat any host that installed it as fully compromised. Isolate the machine, remove the package, rotate all credentials it could reach, and rebuild from a trusted image rather than cleaning in place — a backdoor may have planted additional persistence.

  3. Did it already run?

    If css-at-scope-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-at-scope-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-2026-021024

References

Credits

  • Amazon Inspector · finder

Detect & block this

O3 blocks css-at-scope-polyfill-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the C2 callback and severs the channel.

Malware detection Runtime egress monitoring

Explore

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css-at-scope-polyfill (npm) malicious package — MAL-2026-17547 | O3 Security