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Malicious package

postcss-gap-fallback-utilnpm

Advisory published Updated

postcss-gap-fallback-util is a confirmed malicious npm package (MAL-2026-17518) 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 postcss-gap-fallback-util (npm)

MAL-2026-17518
Immediate action
Remove the package, then rotate any secrets the build/runtime could reach.
npm uninstall postcss-gap-fallback-util

What this malware does

The package is published as a PostCSS gap fallback utility but ships thunderboltRegistry.js, which executes an IIFE on module load. The IIFE runs whoami, id, and hostname via child_process.execSync, curls the AWS instance metadata service at http://169.254.169.254/latest/meta-data/ for IAM role, instance-id, availability zone, and local IPv4, and sends the results to https://webhook.site/0492a36c-4d7b-408a-865c-226db25987ba along with DNS beacons to a host under oast.live. A registry-manifest.min.json maps multiple Wix-internal registry names (thunderboltRegistry, siteAssetsRegistry, documentManagementRegistry, editorRegistry, corvidRegistry, dataBindingRegistry, thunderboltBuilderRegistry, thunderboltPreviewRegistry) to the same exfiltration file, and the module exports a Proxy returning no-op registry methods as a façade. The naming, manifest, and façade indicate a dependency-confusion payload targeting Wix build infrastructure; on any installer that requires one of the impersonated module names, shell identity, hostname, and (on EC2) AWS IAM role credentials/metadata are leaked to an attacker-controlled webhook and DNS collector.

Malicious versions

1 flagged
1.0.0

Indicators of compromise (SHA-256)

5b54d5bd893bc377a77503059998e01ae3e338fd4d8ddac6fe2d7c71a3157cb5

Detection & response playbook

Credential / info stealer

  1. Find it

    Search your lockfiles and build artifacts for postcss-gap-fallback-util (version 1.0.0).

  2. If you installed it — respond

    postcss-gap-fallback-util 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 postcss-gap-fallback-util 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. postcss-gap-fallback-util 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-2026-020962

References

Credits

  • Amazon Inspector · finder

Detect & block this

O3 blocks postcss-gap-fallback-util-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the credential exfiltration and severs the channel.

Malware detection Runtime egress monitoring

Explore

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postcss-gap-fallback-util (npm) malicious package — MAL-2026-17518 | O3 Security