@zynkit/jwtbytesnpm
@zynkit/jwtbytes is a confirmed malicious npm package (MAL-2026-6313) that steals credentials and exfiltrates sensitive data (malicious versions 0.4.3, 0.5.1, 0.5.2…). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in @zynkit/jwtbytes (npm)
What this malware does
@zynkit/jwtbytes (malicious version 0.5.3, published by [email protected]) is a trojanized npm package belonging to the wshu.net credential-stealer campaign. The campaign published trojanized look-alike utility packages across 12+ scopes whose publisher accounts all follow the pattern <scope>-<6 random chars>@wshu.net, with every scope created on June 4, 2026 in a ~40-minute burst. This package masquerades as a JWT byte helper and ships real, working utility code (decoy base32/58/64/hex/ascii85 encoders) so it passes a glance, while bundling a much larger malicious payload at dist/prelude.cjs. package.json declares a postinstall hook ("node dist/prelude.cjs") that runs the payload automatically on npm install. The payload is heavily obfuscated with javascript-obfuscator (hex-named identifiers, a while (!![]) array-rotation IIFE, base64+RC4 string decoding, control-flow flattening, and runtime-decrypted module resolution to stay out of the static module graph). At runtime it is a Chromium browser credential stealer: it reads Chromium Cookies and Login Data and decrypts saved passwords protected by AES-256-GCM (the v10/v11 app-bound key schemes), then exfiltrates them over HTTPS using a spoofed Mozilla/5.0 user agent. Malicious payload dist/prelude.cjs SHA-256: d06ee17d30ebb333ab2e5b6e8a1324fcf95edaaae17b6793ec0f3647338efda1.
The package's main entry dist/mod.cjs begins with require('./prelude.cjs').runPrepare();, so any require('@zynkit/jwtbytes') auto-runs a 280 KB obfuscator.io-style IIFE in dist/prelude.cjs. The IIFE uses an RC4+base64 string-array decoder, anti-debug traps (RegExp/setInterval, console neutralization, --inspect/--inspect-brk checks), and AES-256-GCM ciphertexts decrypted with XOR-derived keys to reconstruct an HTTPS URL at runtime. It then re-execs the current Node process with a sentinel environment variable, fetches a payload to os.tmpdir(), marks it executable, and spawns it via process.execPath or /bin/sh -c. The legitimate codec sources from github.com/dahlia/byte-encodings are bundled verbatim under an unrelated publisher (zynkit <[email protected]>) while reusing the upstream homepage/repository URLs as a lure; the prelude.cjs loader is not present upstream and has been grafted on. The obfuscated loader (~280 KB) dwarfs the ~4 KB of advertised codec source. Importing this package in a developer or CI environment results in remote code execution under attacker control.
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.
Malicious versions
Indicators of compromise (SHA-256)
Detection & response playbook
Credential / info stealerFind it
Scan your lockfiles (package-lock.json, pnpm-lock.yaml, yarn.lock, requirements.txt, poetry.lock, etc.) and build artifacts for @zynkit/jwtbytes (5 malicious versions). O3 Security's supply-chain scanner checks every dependency against known-malicious package intelligence at install time and in CI, flagging @zynkit/jwtbytes across your stack and pipelines.
If you installed it — respond
@zynkit/jwtbytes 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 @zynkit/jwtbytes was ever installed, its post-install/runtime payload may have already executed. O3's L7 egress monitoring and runtime eBPF sensors detect the credential exfiltration or command-and-control callback after install and block the malicious outbound channel, so you catch and contain the actual compromise — not just the presence of the package.
How O3 protects you
O3 blocks @zynkit/jwtbytes before install through its supply-chain scanner, and if it has already run, detects and severs the exfiltration or C2 callback at runtime through L7 egress monitoring and eBPF.
Frequently asked questions
Campaign
References
Credits
- Amazon Inspector · finder
- SafeDep · finder
Detect & block this
O3 blocks @zynkit/jwtbytes-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the credential exfiltration and severs the channel.