claims-format-datenpm
Advisory published Updated
claims-format-date is a confirmed malicious npm package (MAL-2026-12616) that executes malicious code on install (malicious version 35.6.5). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in claims-format-date (npm)
What this malware does
[email protected] auto-executes a binary dropper when the module is required. index.js requires./init on load; init.js downloads a platform-specific binary from string-split-obfuscated Cloudflare Workers hosts (oob-worker.cf102-baf.workers.dev, oob-worker.cf100-416.workers.dev, oob-worker.cf101-adf.workers.dev, oob-worker.cf99-9b3.workers.dev) with a DNS TXT base64-chunk fallback through sdk.dl.wel1.ru, ext.dl.wel1.ru, pkg.dl.wel1.ru, and net.dl.wel1.ru. The fetched bytes are written to /tmp or %TEMP% under disguised names (.cache<uid>, dotnet_diag<uid>.exe), chmod 0755, and detached-spawned via /bin/sh -c or cmd.exe /c start /b. Hostnames and sensitive API references are reconstructed at runtime through array joins and string concatenation (require("child_"+"process"), fs["chmod"+"Sync"]) to evade static analysis. A second parallel dropper implementation in lib/telemetry.js decodes a base64 buffer and performs the same write/chmod/exec chain under an 'analytics SDK' cover story. The package name resembles common date-formatting utilities but the shipped code implements remote payload execution on require.
Malicious versions
Indicators of compromise (SHA-256)
Detection & response playbook
Malicious packageFind it
Search your lockfiles and build artifacts for claims-format-date (version 35.6.5).
If you installed it — respond
Remove claims-format-date 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-format-date 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-format-date-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.