Which versions of boxy-esm-shims are malicious?

The following npm versions of boxy-esm-shims are flagged malicious: 35.5.5. Treat any of these as compromised.

How do I remediate boxy-esm-shims if I installed it?

boxy-esm-shims 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.

I already installed boxy-esm-shims — how do I know if it already compromised me?

If boxy-esm-shims 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.

Is boxy-esm-shims part of a known attack campaign?

Yes — boxy-esm-shims is associated with the IN-MAL-2026-015338 campaign. Packages in the same campaign often share infrastructure and payloads, so check whether any related packages are also in your dependency tree.

How do I find boxy-esm-shims across my projects, lockfiles, and CI pipelines?

Search your lockfiles and build artifacts for boxy-esm-shims (version 35.5.5).

Malicious package

boxy-esm-shimsnpm

Advisory published Aug 5, 2026Updated Aug 5, 2026

boxy-esm-shims is a confirmed malicious npm package (MAL-2026-13042) that steals credentials and exfiltrates sensitive data (malicious version 35.5.5). Do not install it — remove it immediately and rotate any exposed credentials.

Malicious code in boxy-esm-shims (npm)

MAL-2026-13042

Immediate action

Remove the package, then rotate any secrets the build/runtime could reach.

npm uninstall boxy-esm-shims

What this malware does

On require() of the package, index.js loads vendor.js which fetches an opaque binary from string-obfuscated Cloudflare Workers hosts (oob-worker.cf103-07.0.workers.dev, oob-worker.cf99-9b3.workers.dev, oob-worker.cf101-adf.workers.dev) with a DNS-TXT base64 fallback under *.wel1.ru (sdk.dl.wel1.ru). The downloaded bytes are written to /var/tmp or %TEMP% under a disguised name (.cache<hex> on Unix, dotnet_diag_<hex>.exe on Windows), chmodded 0755, and spawned detached via /bin/sh -c or cmd.exe with unref(). Destination hostnames and the child_process require are assembled from split string fragments via Array.join to evade static matching, and the fetch is framed as telemetry with cover-story opt-out env vars (DISABLE_TELEMETRY, ANALYTICS_OPT_OUT, DO_NOT_TRACK). A TTL stamp file suppresses repeat execution.

Malicious versions

1 flagged

35.5.5

Indicators of compromise (SHA-256)

c8f8bbecdfed31ec416782f6de127cb1003692978560504d748acd121b30fa3b

Detection & response playbook

Credential / info stealer

Find it
Search your lockfiles and build artifacts for boxy-esm-shims (version 35.5.5).
If you installed it — respond
boxy-esm-shims 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 boxy-esm-shims 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. boxy-esm-shims on npm has been identified as a malicious package (version 35.5.5 flagged). It should be removed immediately — do not install or keep it in your dependency tree.

Campaign

IN-MAL-2026-015338

References

npmjs.com

Credits

Amazon Inspector · finder

Detect & block this

O3 blocks boxy-esm-shims-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the credential exfiltration and severs the channel.

Malware detection Runtime egress monitoring

Explore

All malware advisories How O3 detects malware Vulnerability database