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)
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
Indicators of compromise (SHA-256)
Detection & response playbook
Credential / info stealerFind it
Search your lockfiles and build artifacts for css-light-dark-polyfill (version 1.0.0).
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.
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
Campaign
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.