MalwarePublished 13 Jun 2026Updated 15 Jul 2026

class-synth (npm) · Malicious Code

Affects class-synthSource GCVE Database

Malicious package : remove class-synth and rotate any secrets on hosts that installed it.

Data as of 15 Jul 2026, 12:36 UTC

Classification

Malicious package

Published to npm · OSV MAL-2026-5730

What to do

Remove class-synth from every project, lockfile and image that pulls it in. Treat any host that installed it as compromised: rotate the credentials, tokens and keys it could read, from a clean machine.

Affected software

Product	Affected	Fixed in
npmclass-synth	Affected 1.0.2 – 1.0.9 8 affected builds	Fixed in–

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Description

--- _-= Per source details. Do not edit below this line.=-_ ## Source: amazon-inspector (1aa63407d7400b4819d0739dedad0a32d9ae29b18509693c2e8763cf30275271) class-synth is advertised as a small class/style/date utility library, but its main entry (dist/index.js) contains a hidden top-level async IIFE (`__init`) that fires whenever the package is required or imported. The IIFE dynamically imports `node:fs`, `node:path`, `node:child_process`, `node:crypto`, and `node:https` using base64-encoded module names joined at runtime to evade string scanners, and acquires `process` indirectly via `new Function('return typeof process!== "undefined"? process: null;')`. It then recursively walks `process.cwd()` looking for any `.css` file containing an `@sri-hash:` marker, base64-decodes that marker, and AES-256-CBC-decrypts it with a hardcoded key (split across an array of hex chunks `['a7b80b01','7e76fb52','fa527621','f76027d2','19014dfc','a59b49ae','3db97ff3','ab4a72fa']`) to recover an attacker-controlled URL. The decrypted URL is fetched over HTTPS and the response body is piped directly into `child_process.spawn('node', ['-'], {windowsHide: true, stdio: ['pipe','ignore','ignore'], detached: true})`, so attacker-supplied JavaScript executes in the developer/CI Node process with no on-disk artifact, suppressed stdio, and a detached/unref'd child. The bundle is padded with ~750 decoy near-duplicate exports (isWithinBoundary1..200, applyPreset1..150, createSequenceStep1..250, mapOperation1..250, checkConstraint1..250) to bury the dropper near the end of the file. The C2 URL is delivered out-of-band via a planted.css file, which defeats URL-based scanning of the package itself. The combination of base64-hidden Node built-ins, split/encrypted C2 location, indirect process access, detached stdin-piped code execution, and large-scale decoy padding leaves no plausible benign reading. ## Source: ghsa-malware (a96165b209ffb2f4e6ad68ae6bcf380d9c70900d080adafcce9110d4ff5c9b71) Any computer that has this package installed or running should be considered fully compromised. All secrets and keys stored on that computer should be rotated immediately from a different computer. The package should be removed, but as full control of the computer may have been given to an outside entity, there is no guarantee that removing the package will remove all malicious software resulting from installing it.

Impact

Any system that installs or runs the affected versions of 'class-synth' is fully compromised. The attacker gains the ability to execute arbitrary JavaScript code remotely within the Node.js process context, potentially leading to complete system takeover, data exfiltration, and further malware deployment. All secrets and keys stored on the compromised system should be considered exposed and rotated immediately. Removal of the package alone does not guarantee eradication of the attacker presence due to the potential for persistent malicious code installed by the attacker.

Defensive guidance

Immediate removal of all affected versions of 'class-synth' from all systems is strongly recommended. Rotate all secrets and credentials that may have been exposed on compromised systems using a separate, trusted environment. Conduct thorough incident response and forensic analysis to identify and remove any additional malicious artifacts or persistence mechanisms. Monitor for any suspicious activity related to Node.js processes and network connections to attacker-controlled domains.

Summary

The 'class-synth' npm package (versions 1.0.2, 1.0.3, 1.0.4, 1.0.5, 1.0.6, 1.0.7, 1.0.8, and 1.0.9) contains a hidden asynchronous immediately-invoked function expression (IIFE) that dynamically imports core Node.js modules using base64-encoded names to evade detection. It accesses the process object indirectly and recursively scans the current working directory for CSS files containing a base64-encoded '@sri-hash:' marker. This marker is AES-256-CBC decrypted with a hardcoded key to reveal an attacker-controlled URL. The package fetches JavaScript code from this URL over HTTPS and executes it in a detached child Node.js process with suppressed input/output, allowing remote code execution without leaving on-disk artifacts. The malicious code is heavily obfuscated with numerous decoy exports to hide its presence. The command-and-control URL is delivered out-of-band via a planted CSS file, defeating URL-based scanning of the package itself. This combination of techniques indicates deliberate and sophisticated malicious intent.

References

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What to do

Affected software

Description

AI analysisMachine-generated, updated 14 Jul 2026, 09:25 UTC

Technical details

References

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