Which versions of express-middle are malicious?

The following npm versions of express-middle are flagged malicious: 5.5.1. Treat any of these as compromised.

How do I remediate express-middle if I installed it?

express-middle 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.

I already installed express-middle — how do I know if it already compromised me?

If express-middle 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.

Is express-middle part of a known attack campaign?

Yes — express-middle is associated with the IN-MAL-2026-014813 campaign. Packages in the same campaign often share infrastructure and payloads, so check whether any related packages are also in your dependency tree.

How do I find express-middle across my projects, lockfiles, and CI pipelines?

Scan your lockfiles (package-lock.json, pnpm-lock.yaml, yarn.lock, requirements.txt, poetry.lock, etc.) and build artifacts for express-middle (version 5.5.1). O3 Security's supply-chain scanner checks every dependency against known-malicious package intelligence at install time and in CI, flagging express-middle across your stack and pipelines.

Malicious package

express-middlenpm

express-middle is a confirmed malicious npm package (MAL-2026-12376) that opens a backdoor for remote access (malicious version 5.5.1). Do not install it — remove it immediately and rotate any exposed credentials.

Malicious code in express-middle (npm)

MAL-2026-12376

Immediate action

Remove the package, then rotate any secrets the build/runtime could reach.

npm uninstall express-middle

What this malware does

package.json declares postinstall: node index.js, which fires automatically on npm install. index.js is a heavily obfuscated bundle (obfuscator.io-style RC4-decoded 344-entry string array with control-flow flattening) whose runtime behavior assembles a destination host at runtime by concatenating four numeric fragments with '.' (an IPv4 built to hide the C2 from static review), performs an HTTPS request to that host, splits the response on ':' into IV and ciphertext, derives a key via pbkdf2, AES-decrypts the response with createDecipheriv, writes the plaintext payload to disk via fs.writeFileSync, and executes it through child_process.exec with windowsHide:true to suppress a console window. The package name resembles express middleware but ships no middleware functionality; the sole effect of installing it is remote code execution on the installer's machine under attacker control.

Malicious versions

1 flagged

5.5.1

Indicators of compromise (SHA-256)

91c0275a4e65fc4ed9930cb89002f2c4ebc50163b292f552703c4ea6a9940567

Detection & response playbook

Backdoor / remote access

Find it
Scan your lockfiles (package-lock.json, pnpm-lock.yaml, yarn.lock, requirements.txt, poetry.lock, etc.) and build artifacts for express-middle (version 5.5.1). O3 Security's supply-chain scanner checks every dependency against known-malicious package intelligence at install time and in CI, flagging express-middle across your stack and pipelines.
If you installed it — respond
express-middle 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.
Did it already run?
If express-middle 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 express-middle 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

No. express-middle on npm has been identified as a malicious package (version 5.5.1 flagged). It should be removed immediately — do not install or keep it in your dependency tree.

Campaign

IN-MAL-2026-014813

References

npmjs.com

Credits

Amazon Inspector · finder

Detect & block this

O3 blocks express-middle-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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