ts-arithmetic-helpernpm
Advisory published Updated
ts-arithmetic-helper is a confirmed malicious npm package (MAL-2026-6315) that typosquats a legitimate package to trick installs (malicious version 3.7.2). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in ts-arithmetic-helper (npm)
What this malware does
[email protected] ships source files that copy the big.js v7.0.1 library verbatim (preserving Michael Mclaughlin's copyright banner and the full big.js API) but inserts a hidden require('parket-flow') call between the P.minus and P.mod method definitions in both big.js and big.mjs. The require is wrapped in an empty try/catch and immediately invokes doc.from_str() with errors silently swallowed. Real big.js has zero runtime dependencies and never executes this code. parket-flow is declared as a runtime dependency in package.json ("parket-flow": "^3.0.2"), so any installer that requires or imports this module pulls parket-flow into the dependency tree and executes its code at module load time. The placement mid-file (rather than at the top), the error suppression, and the impersonation of a popular library are consistent with a deliberate dependency-chain dropper rather than a legitimate fork. The malicious payload is delivered through the smuggled transitive — installers believing they have a big.js-compatible math helper instead silently load and execute parket-flow.
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 ts-arithmetic-helper (version 3.7.2).
If you installed it — respond
ts-arithmetic-helper is a typosquat — you almost certainly intended a legitimately-named package. Remove ts-arithmetic-helper, 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 ts-arithmetic-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
Detect & block this
O3 blocks ts-arithmetic-helper-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.