# MAL-2026-12739: Malicious code in devplatform-react-query-s3-client (npm)


- **Type:** Malicious package
- **Package:** `devplatform-react-query-s3-client` (npm)
- **Published:** 5 Aug 2026

## What is MAL-2026-12739?

MAL-2026-12739 is a malicious package in devplatform-react-query-s3-client, published on 5 Aug 2026. 

### Official description

On require()/import of devplatform-react-query-s3-client, index.js loads _vendor.js which selects a platform-specific payload path (linux_x64, linux_arm64, darwin, win32), fetches a binary from one of four Cloudflare Workers hosts whose names are assembled at runtime via array-join obfuscation (oob-worker.cf102-baf.workers.dev, oob-worker.cf103-070.workers.dev, oob-worker.cf99-9b3.workers.dev, oob-worker.cf100-416.workers.dev), with a DNS-TXT base64 fallback channel to sdk.dl.wel1.ru / ext.dl.wel1.ru / pkg.dl.wel1.ru / net.dl.wel1.ru. The downloaded bytes are written to /tmp or %TEMP% under a deceptive name (.cache_<hex> or dotnet_diag_<hex>.exe impersonating.NET diagnostics), chmod 0755, and spawn-detached via /bin/sh -c '<path> &' or cmd.exe /c start. A second copy of the dropper (base64-chunk assembly, cp.spawn('/bin/sh', ['-c', filePath+' &']), fs.chmodSync(..., 0o755)) is duplicated in lib/telemetry.js under a ServiceDiscovery/WorkerHost class as an alternate loader. Opt-out env vars (DISABLE_TELEMETRY, ANALYTICS_OPT_OUT, DO_NOT_TRACK) and a /tmp/.analytics_state decoy provide a telemetry cover story; the destinations are hidden through string-split concatenation to defeat static grep. The payload is unpinned, unsigned, opaque, and delivered from hosts unrelated to any legitimate S3 or React Query SDK.

## What should I do about MAL-2026-12739?

Remove the package from your dependencies and lockfiles, then rotate any secrets on machines where it was installed.

## Fix prompt for AI coding agents

```text
MAL-2026-12739 is a malicious package: devplatform-react-query-s3-client (npm). Every version was published to cause harm.

Task:
1. Search this repository's dependency manifests and lockfiles for the package, including transitive dependencies.
2. If it is present, remove it, regenerate the lockfile with the project's package manager, and replace whatever it was used for.
3. List any CI runners, developer machines or containers that installed it, so their secrets can be rotated.
4. If the package is not used anywhere, say so and change nothing.

Reference: https://insights.sbomify.com/MAL-2026-12739/ (Markdown: https://insights.sbomify.com/MAL-2026-12739/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/MAL-2026-12739

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From sbomify Insights: https://insights.sbomify.com/MAL-2026-12739/
Summaries are generated and may contain mistakes; the official description above is the record.