logfmt-corenpm
logfmt-core is a confirmed malicious npm package (MAL-2026-6437) that executes malicious code on install (malicious versions 3.1.0, 3.2.0, 3.3.0…). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in logfmt-core (npm)
What this malware does
On npm install, scripts/install-check.cjs (registered as a postinstall lifecycle script) fetches a JSON config from a hardcoded anonymous Vercel app URL (https://vercel-backend-myapp.vercel.app/config/logfmt-sync.json), parses it to obtain a.tgz bundle URL, downloads the tarball to /tmp, extracts it with tar -xzf, runs npm install inside the extracted directory (causing any lifecycle scripts in the fetched package to also run), then require()s peer-math.js from the bundle and invokes syncSession(). The fetched code is unpinned, unauthenticated, not hash-verified, not hosted on the publisher's domain, and unrelated to the package's stated purpose (a logging-format utility offering createLogger, formatCurrency, roundDecimal). The package author controls the Vercel endpoint and can change the delivered bytes at any time, giving them arbitrary code execution on every machine that installs logfmt-core. Naming choices (install-check, resolvePeerBundleUrl, runPeerSync, syncSession) and a benign-looking [logfmt-core] install check skipped error log are framed to resemble a routine peer-dependency check rather than a remote-payload loader.
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
Malicious packageFind it
Scan your lockfiles (package-lock.json, pnpm-lock.yaml, yarn.lock, requirements.txt, poetry.lock, etc.) and build artifacts for logfmt-core (4 malicious versions). O3 Security's supply-chain scanner checks every dependency against known-malicious package intelligence at install time and in CI, flagging logfmt-core across your stack and pipelines.
If you installed it — respond
Remove logfmt-core from your project and lockfile, then assume any secrets accessible to the build or runtime were exposed: rotate API keys, tokens, and credentials, and audit for unexpected outbound activity or persistence.
Did it already run?
If logfmt-core 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 logfmt-core 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 logfmt-core-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.