num-format-helpernpm
Advisory published Updated
num-format-helper is a confirmed malicious npm package (MAL-2026-11107) that steals credentials and exfiltrates sensitive data (malicious version 1.0.0). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in num-format-helper (npm)
What this malware does
Package advertises itself as a number/locale formatting helper but its postinstall.js runs automatically on npm install and shells out via child_process/exec to collect host identity (hostname, user, id, sudo, uname), GitHub Actions variables including GITHUB_TOKEN and GITHUB_REPOSITORY, a broad env dump filtered by a credential regex (KEY|TOKEN|SECRET|CREDENTIAL|KUBE|JENKINS|NPM|GEM|CARGO|AZURE|GCP|AWS_|GH_TOKEN|GITHUB_TOKEN), network interfaces, running processes, and cloud instance metadata (AWS 169.254.169.254, Aliyun 100.100.100.200, Tencent). The collected data is base64-encoded and sent via curl in a GET request to the hardcoded Burp Collaborator subdomain pzs5w7ntzhsnepwk564lyfdci3oucl0a.oastify.com. The shipped index.js is a trivial unrelated stub, confirming the package is a cover story for the install-time exfiltration payload.
The OpenSSF Package Analysis project identified 'num-format-helper' @ 1.0.0 (npm) as malicious.
It is considered malicious because:
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The package communicates with a domain associated with malicious activity.
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The package executes one or more commands associated with malicious behavior.
Malicious versions
Indicators of compromise (SHA-256)
Detection & response playbook
Credential / info stealerFind it
Search your lockfiles and build artifacts for num-format-helper (version 1.0.0).
If you installed it — respond
num-format-helper 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 num-format-helper 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
- OpenSSF: Package Analysis · finder
Detect & block this
O3 blocks num-format-helper-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the credential exfiltration and severs the channel.