express-session-jsnpm
Advisory published Updated
express-session-js is a confirmed malicious npm package (MAL-2026-2419) that typosquats a legitimate package to trick installs (malicious version 1.0.0). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in express-session-js (npm)
What this malware does
Package impersonates legitimate express-session package; initPlugin() downloads and executes attacker-controlled remote code on startup via new Function.constructor()
The package express-session-js was found to contain malicious code.
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
TyposquatFind it
Search your lockfiles and build artifacts for express-session-js (version 1.0.0).
If you installed it — respond
express-session-js is a typosquat — you almost certainly intended a legitimately-named package. Remove express-session-js, install the correct package, and rotate any secrets exposed during the install since post-install scripts may have already run.
Did it already run?
If express-session-js 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
Campaign
References
Credits
- Amazon Inspector · finder
- SafeDep · finder
Detect & block this
O3 blocks express-session-js-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the malicious outbound activity and severs the channel.