Your RSA-2048 keys break in 2030. Find every one of them before attackers do.
Malicious package

css-light-dark-polyfillnpm

Advisory published Updated

css-light-dark-polyfill is a confirmed malicious npm package (MAL-2026-17481) 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-light-dark-polyfill (npm)

MAL-2026-17481
Immediate action
Remove the package, then rotate any secrets the build/runtime could reach.
npm uninstall css-light-dark-polyfill

What this malware does

The package presents itself as a trivial CSS polyfill (index.js exports an empty object) but ships thunderboltRegistry.js, which on load runs a self-invoking IIFE that collects host identifiers (os.hostname, node version, platform, pid) and the output of local shell commands (id, whoami, uname -a, ifconfig/ip addr, /etc/hosts via child_process.execSync) and POSTs each result via fetch() to the hardcoded endpoint https://dxpoc.gt.tc/callback.php/. The payload self-labels as 'beacon=rce-poc'. The package also exports factories under the names of internal Wix Thunderbolt build registries (thunderboltRegistry, siteAssetsRegistry, documentManagementRegistry, editorRegistry, etc.), and a bundled registry-manifest.min.json maps those names to parastorage.com URLs — a dependency-confusion shape targeting Wix-like build systems that resolve these internal registry module names. Installing or loading this package causes host reconnaissance data to be exfiltrated to an attacker-controlled domain unrelated to any CSS polyfill functionality.

Malicious versions

1 flagged
1.0.0

Indicators of compromise (SHA-256)

856c154d7855924568c88181f172f46e84aac202bd6cb29974eb2ffaa3ec3ea7

Detection & response playbook

Credential / info stealer
  1. Find it

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

  2. If you installed it — respond

    css-light-dark-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-light-dark-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-light-dark-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-2026-020889

References

Credits

  • Amazon Inspector · finder

Detect & block this

O3 blocks css-light-dark-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-light-dark-polyfill (npm) malicious package — MAL-2026-17481 | O3 Security