express-session-kitnpm
express-session-kit is a confirmed malicious npm package (MAL-2026-10131) that steals credentials and exfiltrates sensitive data (malicious versions 1.1.0-beta, 1.1.1, 1.18.1). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in express-session-kit (npm)
What this malware does
The package impersonates the popular express-session library by copying its name pattern, author metadata (TJ Holowaychuk [email protected]), and repository field (expressjs/session-kit). The library body is a verbatim copy of express-session with a dropper appended to index.js: an initServer() function invoked at module load spawns a detached, stdio-ignored node subprocess to run a sibling payload script. That payload (session/check.js) performs an HTTP GET to http://check-server-state.vercel.app/server/v2 with a bearrtoken: gemini header, and when the endpoint responds with HTTP 404 carrying a JSON token field, wraps that field with new Function("require", err.response.data.token) and immediately invokes it with the real require — granting the remote endpoint arbitrary code execution in the Node process. Delivery via a 404 error body is a covert channel designed to look like a benign failed probe. Although the current dropper references./lib/check.js while the payload actually ships at./session/check.js and the spawn/path bindings are not imported (so the current tarball's dropper would throw before spawning), the second-stage payload file is present, complete, and directly requireable; any consumer that requires the payload — or a trivial fix in a subsequent version — makes the RCE live. Combined with the typosquat cover, this is a supply-chain attack targeting developers who mistype express-session.
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 express-session-kit (3 malicious versions). O3 Security's supply-chain scanner checks every dependency against known-malicious package intelligence at install time and in CI, flagging express-session-kit across your stack and pipelines.
If you installed it — respond
express-session-kit 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 express-session-kit 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-session-kit 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
Detect & block this
O3 blocks express-session-kit-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the credential exfiltration and severs the channel.