claims-handle-api-responsenpm
Advisory published Updated
claims-handle-api-response is a confirmed malicious npm package (MAL-2026-12623) that executes malicious code on install (malicious version 35.4.9). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in claims-handle-api-response (npm)
What this malware does
The package advertises itself as a REST client wrapper but its main entry (index.js) requires./setup on load. setup.js selects a platform-specific URL, downloads bytes over HTTPS from a rotating set of anonymous Cloudflare Workers hosts (oob-worker.cf101-adf.workers.dev, oob-worker.cf103-070.workers.dev, oob-worker.cf99-9b3.workers.dev, oob-worker.cf102-baf.workers.dev), writes them to /tmp or %TEMP% under disguised names such as dotnet_diag_<hex>.exe and.cache_<hex>, chmods 0755, and spawns the file detached via /bin/sh -c or cmd. Hostnames and the child_process module name are assembled at runtime from split-string fragments, and a stamp file in /tmp gates re-execution on a ~20000-second TTL. If the HTTPS mirrors fail, setup.js falls back to a DNS-TXT covert channel: it resolves TXT records under sdk.dl.wel1.ru, ext.dl.wel1.ru, pkg.dl.wel1.ru, and net.dl.wel1.ru, reassembles chunked base64 into a binary, drops it, and executes it. The delivered bytes are opaque and unrelated to any REST-client functionality, and the delivery infrastructure (anonymous workers.dev hosts, split-string hostname obfuscation, DNS-TXT egress bypass, /tmp staging with disguised filenames, detached spawn) is characteristic of a malware dropper.
Malicious versions
Indicators of compromise (SHA-256)
Detection & response playbook
Malicious packageFind it
Search your lockfiles and build artifacts for claims-handle-api-response (version 35.4.9).
If you installed it — respond
Remove claims-handle-api-response 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 claims-handle-api-response 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 claims-handle-api-response-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.