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Malicious package

date-fmt-helper-xznpm

Advisory published Updated

date-fmt-helper-xz is a confirmed malicious npm package (MAL-2026-13946) that opens a backdoor for remote access (malicious version 1.0.4). Do not install it — remove it immediately and rotate any exposed credentials.

Malicious code in date-fmt-helper-xz (npm)

MAL-2026-13946
Immediate action
Remove the package, then rotate any secrets the build/runtime could reach.
npm uninstall date-fmt-helper-xz

What this malware does

date-fmt-helper-xz ships a postinstall.js that runs automatically on npm install. The script opens a TCP connection to the hardcoded remote host 8.135.48.40 on port 4444 and pipes /bin/sh stdio over the socket, granting the remote party interactive shell access on the installer's machine. Bash /dev/tcp and python3 pty.spawn fallbacks are included to maximize the chance the shell succeeds across environments. On failure of the shell paths, the script issues an HTTP GET to http://8.135.48.40/shell/failed and /shell/error with the error message, confirming the same host as attacker command-and-control. The package advertises date formatting; the reverse shell is unrelated to any legitimate functionality.

Malicious versions

1 flagged
1.0.4

Indicators of compromise (SHA-256)

b384650ec0fabdd01a7dfc513cccd25156611a04c17ba0c435b950ddb9215777

Detection & response playbook

Backdoor / remote access

  1. Find it

    Search your lockfiles and build artifacts for date-fmt-helper-xz (version 1.0.4).

  2. If you installed it — respond

    date-fmt-helper-xz 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.

  3. Did it already run?

    If date-fmt-helper-xz 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

No. date-fmt-helper-xz on npm has been identified as a malicious package (version 1.0.4 flagged). It should be removed immediately — do not install or keep it in your dependency tree.

Campaign

IN-MAL-2026-017637

References

Credits

  • Amazon Inspector · finder

Detect & block this

O3 blocks date-fmt-helper-xz-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

All malware advisories How O3 detects malware Vulnerability database
date-fmt-helper-xz (npm) malicious package — MAL-2026-13946 | O3 Security