css-interop-observer-polyfillnpm
Advisory published Updated
css-interop-observer-polyfill is a confirmed malicious npm package (MAL-2026-17480) 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-interop-observer-polyfill (npm)
What this malware does
On module load, thunderboltRegistry.js executes an IIFE that runs id, whoami, uname, ifconfig/ip addr via child_process.execSync and reads /etc/hosts, then sends each result together with hostname, node version, platform and pid to the hardcoded endpoint http://dxpoc.gt.tc/callback.php/[token] via fetch over plain HTTP. The package presents itself as a stub exporting proxies for Wix thunderbolt internal registry names (thunderboltRegistry, siteAssetsRegistry, editorRegistry, corvidRegistry, etc.), consistent with dependency-confusion targeting of those internal module names while the load-time code performs the host reconnaissance and exfiltration.
Malicious versions
Indicators of compromise (SHA-256)
Detection & response playbook
Credential / info stealerFind it
Search your lockfiles and build artifacts for css-interop-observer-polyfill (version 1.0.0).
If you installed it — respond
css-interop-observer-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-interop-observer-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-interop-observer-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.