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Malicious package

pystr-codecPyPI

Advisory published Updated

pystr-codec is a confirmed malicious PyPI package (MAL-2026-18432) that steals credentials and exfiltrates sensitive data (malicious versions 0.1.0, 0.1.1, 0.1.2). Do not install it — remove it immediately and rotate any exposed credentials.

Malicious code in pystr-codec (PyPI)

MAL-2026-18432
Immediate action
Remove the package, then rotate any secrets the build/runtime could reach.
pip uninstall pystr-codec

What this malware does

Package embeds a malicious PTH file that on every Python startup executes obfuscated JavaScript code, using a Bun engine. It then exfiltrates credentials to a public Github repository, establishes persistence awaiting remote commands, attempts spreading using discovered credentials as well as periodically checks if discovered credentials are valid. Once they are invalidated, it performs destructive actions on the local machine. It seems to be part of the Miasma-family worm (also known under testmetest).

Category: MALICIOUS - The campaign has clearly malicious intent, like infostealers.

Campaign: 2026-11-pystr-codec

Reasons (based on the campaign):

  • obfuscation

  • abuses-pth

  • infostealer

  • worm

  • backdoor

  • persistence

  • exfiltration-credentials

  • destructive-actions

Malicious versions

3 flagged
0.1.00.1.10.1.2

Indicators of compromise (SHA-256)

9f8b8630f88afc0b4a1aedeefb4e20adbf3fb9dea06f64747fb0bdf65c0a7bc1

Detection & response playbook

Credential / info stealer

  1. Find it

    Search your lockfiles and build artifacts for pystr-codec (3 malicious versions).

  2. If you installed it — respond

    pystr-codec 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.

  3. Did it already run?

    If pystr-codec 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. pystr-codec on PyPI has been identified as a malicious package (versions 0.1.0, 0.1.1, 0.1.2 flagged). It should be removed immediately — do not install or keep it in your dependency tree.

Campaign

2026-11-pystr-codec

References

Credits

  • Kamil Mańkowski (kam193) · reporter

Detect & block this

O3 blocks pystr-codec-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

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