Malicious code in chai-as-format (npm)
The npm package chai-as-format contained malicious obfuscated code that executes automatically on import. The package impersonated the unrelated pino logging framework while shipping a ~4MB hex-encoded trojan loader disguised as a config module.
- Disclosed
- Last updated
- Blast radius
- Any developer or system that installed the malicious chai-as-format package from npm.
- Ecosystems
- Attack vectors
- Affected entities
- chai-as-formatnpm package containing obfuscated trojan loader
The npm package chai-as-format was found to contain malicious code in its index.js file, which unconditionally requires a ~4MB obfuscated module named ./lib/config. This obfuscated code uses obfuscator.io-style encoding with a 23,953-entry hex-encoded string array and heavy control-flow flattening, executing automatically whenever the package is imported.\n\nThe package employed a deceptive impersonation strategy: its README, LICENSE, and documentation were copied from the unrelated pino logging framework (with LICENSE attribution to pinojs/pino), while the package.json description referenced vulnerability management. This mismatch between the cover story and actual shipped content indicates intentional obfuscation of the package's true purpose.\n\nThe multi-megabyte opaque decoder auto-loaded on import is not a legitimate configuration module but rather a trojan loader hidden behind an impersonation shell. The malicious code would execute on the installer's machine whenever the package was required.\n\nThe incident was identified and credited to the OpenSSF's malicious-packages repository.
Indicators of compromise
- Packages
- chai-as-format
Remediation
- Immediately remove chai-as-format from all projects and dependencies
- Audit npm install logs to identify when the package was installed
- Review systems where the package was installed for signs of compromise or unauthorized activity
- Regenerate any credentials or signing keys that may have been exposed on affected systems
- Update to a legitimate alternative if the intended functionality is needed
- Check npm audit and dependency scanning tools for detection of this malicious package
Sources
- GitHub Advisory GHSA-wpwv-ffg9-hmxr · GitHub Advisory Database
Cite this entry
"Malicious code in chai-as-format (npm)." supplychainattack.org, Supply Chain Attack Incident Catalog. Disclosed August 10, 2026; last updated August 10, 2026. https://supplychainattack.org/incident/malicious-code-in-chai-as-format-npm-hu3vzg
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