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Malicious package

arbocrate-sla-prober-arbocrate-sla-prober-corenpm

Advisory published Updated

arbocrate-sla-prober-arbocrate-sla-prober-core is a confirmed malicious npm package (MAL-2026-12140) that typosquats a legitimate package to trick installs (malicious versions 7.5.6, 7.5.7, 7.5.8…). Do not install it — remove it immediately and rotate any exposed credentials.

Malicious code in arbocrate-sla-prober-arbocrate-sla-prober-core (npm)

MAL-2026-12140
Immediate action
Remove the package, then rotate any secrets the build/runtime could reach.
npm uninstall arbocrate-sla-prober-arbocrate-sla-prober-core

What this malware does

On require() of the package, index.js loads setup.js, which resolves the running platform and architecture, downloads a platform-specific binary from hardcoded Cloudflare Workers endpoints (package-proxy.cf5oobworker.workers.dev, package-proxy.cf8oobworker.workers.dev, package-proxy.cf12oobworker.workers.dev, package-proxy.cf17-ddb.workers.dev, package-proxy.cf25-6eb.workers.dev) and fallback hosts under well1.site (tin.dl.well1.site, tina.dl.well1.site, ldr.dl.well1.site, win.dl.well1.site) at paths /pkg/package, /pkg/package-arm64, /pkg/loader_mac, /pkg/package.exe, writes the fetched bytes to a temp path, chmods 0755, and executes them via child_process. The sensitive APIs and destination hostnames are reconstructed at runtime through string concatenation and array-join tricks (require("child_"+"process"), os["plat"+"form"], fs["chmod"+"Sync"], hostnames assembled from split fragments) to evade static keyword scanners. Before contacting the remote hosts, setup.js hashes hostname, OS username, cwd, node version, and pid into an install fingerprint and passes it to the transport as an installId, letting the operator track each installer host receiving the payload. Destinations are anonymous Cloudflare Workers subdomains and a lookalike well1.site host, unrelated to any legitimate publisher infrastructure; fetched content is unversioned, unhashed, and unsigned.

Malicious versions

5 flagged
7.5.67.5.77.5.87.5.912.7.1

Indicators of compromise (SHA-256)

1bcfaaf88e12fe23f911d31199e07bae2134691cb1ae511ca187fa62328f165e
34a4b9e0346198bed7019ba0bba4e32036dad95c22d83159b22ab5e9920bd8f0
3bf47a8288a6843faf05f01d7b4f27e8389baf2e171130e7f011b95d17dfc04c
c0a304d2d0daa291ff873f9036d109f3fd0b7c9e79f446980b70e3435ff04a04
edbd819d3b041fefa079889ce29fcd3f55b24e7091f8002b220ee5a593844f79

Detection & response playbook

Typosquat
  1. Find it

    Search your lockfiles and build artifacts for arbocrate-sla-prober-arbocrate-sla-prober-core (5 malicious versions).

  2. If you installed it — respond

    arbocrate-sla-prober-arbocrate-sla-prober-core is a typosquat — you almost certainly intended a legitimately-named package. Remove arbocrate-sla-prober-arbocrate-sla-prober-core, install the correct package, and rotate any secrets exposed during the install since post-install scripts may have already run.

  3. Did it already run?

    If arbocrate-sla-prober-arbocrate-sla-prober-core 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

No. arbocrate-sla-prober-arbocrate-sla-prober-core on npm has been identified as a malicious package (versions 7.5.6, 7.5.7, 7.5.8, 7.5.9, 12.7.1 flagged). It should be removed immediately — do not install or keep it in your dependency tree.

Campaign

IN-MAL-2026-014623IN-MAL-2026-014625IN-MAL-2026-014621IN-MAL-2026-014624IN-MAL-2026-014626

References

Credits

  • Amazon Inspector · finder

Detect & block this

O3 blocks arbocrate-sla-prober-arbocrate-sla-prober-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.

Explore

arbocrate-sla-prober-arbocrate-sla-prober-core (npm) malicious package — MAL-2026-12140 | O3 Security