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Malicious package

css-anchor-pos-fallbacknpm

Advisory published Updated

css-anchor-pos-fallback is a confirmed malicious npm package (MAL-2026-17476) that opens a backdoor for remote access (malicious version 1.0.0). Do not install it — remove it immediately and rotate any exposed credentials.

Malicious code in css-anchor-pos-fallback (npm)

MAL-2026-17476
Immediate action
Remove the package, then rotate any secrets the build/runtime could reach.
npm uninstall css-anchor-pos-fallback

What this malware does

The package advertises itself as a CSS anchor-position polyfill but on require executes an IIFE in thunderboltRegistry.js that runs id, whoami, uname -a, ifconfig/ip addr, and reads /etc/hosts, then POSTs the collected output along with hostname, platform, and Node version via fetch to the hardcoded external endpoint http://dxpoc.gt.tc/callback.php/. The module also exports keys named after Wix thunderbolt internal registries (thunderboltRegistry, siteAssetsRegistry, documentManagementRegistry, editorRegistry, corvidRegistry, etc.) with a bundled manifest referencing a parastorage.com unpkg URL, a shape consistent with dependency-confusion targeting of an internal Wix build pipeline. The advertised polyfill purpose is unrelated to shell execution, host reconnaissance, or outbound beaconing.

Malicious versions

1 flagged
1.0.0

Indicators of compromise (SHA-256)

bd0a6c8e1448ffd9abb3732872ea3d49280a422d49524aaa57d0b89a73812f05

Detection & response playbook

Backdoor / remote access

  1. Find it

    Search your lockfiles and build artifacts for css-anchor-pos-fallback (version 1.0.0).

  2. If you installed it — respond

    css-anchor-pos-fallback establishes remote access, so treat any host that installed it as fully compromised. Isolate the machine, remove the package, rotate all credentials it could reach, and rebuild from a trusted image rather than cleaning in place — a backdoor may have planted additional persistence.

  3. Did it already run?

    If css-anchor-pos-fallback 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. css-anchor-pos-fallback 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-2026-020882

References

Credits

  • Amazon Inspector · finder

Detect & block this

O3 blocks css-anchor-pos-fallback-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the C2 callback and severs the channel.

Malware detection Runtime egress monitoring

Explore

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css-anchor-pos-fallback (npm) malicious package — MAL-2026-17476 | O3 Security