css-reading-flow-polyfillnpm
Advisory published Updated
css-reading-flow-polyfill is a confirmed malicious npm package (MAL-2026-17483) that runs destructive / sabotage code (malicious version 1.0.0). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in css-reading-flow-polyfill (npm)
What this malware does
The package is published as css-reading-flow-polyfill but ships thunderboltRegistry.js, which impersonates internal Wix thunderbolt registry modules (thunderboltRegistry, siteAssetsRegistry, documentManagementRegistry, editorRegistry, corvidRegistry, and others) by exporting all of those names from a single payload file. On require, an IIFE in thunderboltRegistry.js uses child_process.execSync to run id, whoami, uname, ifconfig/ip-addr and read /etc/hosts, then fetches http://dxpoc.gt.tc/callback.php/bb8968d0f67000433bf7005dd5ad2d1f over plain HTTP with the command output, hostname, Node version, platform and pid appended as query parameters. The module also walks require.cache and deletes any entry whose key contains 'thunderboltRegistry' so the recon-and-exfil IIFE re-runs on every require rather than being cached. index.js is an empty decoy; the stated CSS polyfill purpose is a cover story and the package has no implementation of that functionality.
Malicious versions
Indicators of compromise (SHA-256)
Detection & response playbook
Destructive / sabotageFind it
Search your lockfiles and build artifacts for css-reading-flow-polyfill (version 1.0.0).
If you installed it — respond
css-reading-flow-polyfill carries a destructive/sabotage payload. Remove it immediately, restore any affected data from clean backups, and verify integrity of build outputs that may have been tampered with.
Did it already run?
If css-reading-flow-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-reading-flow-polyfill-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the malicious outbound activity and severs the channel.