css-flow-render-shimnpm
Advisory published Updated
css-flow-render-shim is a confirmed malicious npm package (MAL-2026-17655) 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-flow-render-shim (npm)
What this malware does
[email protected] was published to npm on 2026-10-06 22:49 UTC by user brahimhamidi (the account's only package). It is described as a CSS polyfill but contains none: index.js is an empty module (byte-identical to the index.js of [email protected]) and payload.min.css is 15 bytes. payload.bundle.min.js carries the payload and runs at require time as a top-level IIFE; it first deletes its own require.cache entries so that it runs again on every require.
Behavior: (1) obtains child_process through require('child_process'), require('node:child_process') or a freshly constructed Module instance if both are blocked (lines 29-31); (2) runs whoami, id, uname -a, env (first 100 lines, 2,000 characters sent), ifconfig || ip addr, and cat /etc/hosts with execSync and sends each output, together with os.hostname() and the tag vector=registryLibrariesTopology, to https://webhook.site/69bcd627-1871-4dda-b880-83b37ceac418 through both fetch and https.get (lines 12-56); the env step exfiltrates the host's environment variables, including any tokens; (3) sends a beacon tagged topology-rce with the Node version, platform, process id and package name (line 60); (4) exports Proxy objects under Wix-internal module names (thunderboltRegistry, siteAssetsRegistry, documentManagementRegistry, editorRegistry, corvidRegistry, dataBindingRegistry, autoCompleteRegistry, thunderboltBuilderRegistry, thunderboltPreviewRegistry), and the two rb_*.thunderbolt.manifest.min.json files list the payload under https://unpkg.com/[email protected]/, which indicates a dependency-confusion attempt against that organization's private packages (lines 65-98).
Trigger: on import (require). Type: information stealer (host identity, network configuration and environment variables). Same collector path as [email protected] (published 2026-10-06 20:21 UTC by user hissakdx92), which performs port scanning and host reconnaissance for the same target, and same payload family as [email protected] and css-eqxcdx-polyfill.
The package publishes an empty index.js stub but ships Thunderbolt manifests that register payload.bundle.min.js as the bundle for core Wix components across the thunderbolt/wixui and thunderbolt/dsgnsys namespaces (Container, MasterPage, Section, StylableButton, WRichText, and others), and the bundle exports factories under names like thunderboltRegistry, editorRegistry, and corvidRegistry. When a Wix Thunderbolt build pipeline resolves this name from the public registry instead of the intended internal package, payload.bundle.min.js is loaded and its top-level IIFE executes immediately. The IIFE uses child_process.execSync to run whoami, id, uname -a, env | head -100, ifconfig/ip addr, and cat /etc/hosts, then URL-encodes each output along with hostname, node version, platform, and pid and sends it via https.get to a hardcoded collector at https://webhook.site/69bcd627-1871-4dda-b880-83b37ceac418. The payload also iterates require.cache and deletes every entry whose path contains payload, rb_wixui, or rb_dsgnsys so the recon routine re-fires on each subsequent require within a long-running build process. The combination of a hollow public package impersonating an internal Wix shim, Thunderbolt-shaped manifests, host and environment reconnaissance via shell commands, exfiltration to an attacker-controlled webhook.site endpoint, and require.cache tampering is a dependency-confusion attack against Wix build systems.
Malicious versions
Indicators of compromise (SHA-256)
Detection & response playbook
Credential / info stealerFind it
Search your lockfiles and build artifacts for css-flow-render-shim (version 1.0.0).
If you installed it — respond
css-flow-render-shim 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-flow-render-shim 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
- Eunsoo Kim · finder
Detect & block this
O3 blocks css-flow-render-shim-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the credential exfiltration and severs the channel.