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Malicious code in pystr-codec (PyPI)

What to do

Vendor response not established. Follow the primary source's mitigation guidance and check back for a fix.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • PyPI pystr-codec

    Affected
    >= 0.1.0, <= 0.1.0>= 0.1.1, <= 0.1.1>= 0.1.2, <= 0.1.2
    Fixed in
    no fixed version recorded

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
not scored
EPSS
No dated EPSS signal available.
Source description

As published by the source; long descriptions are shortened.

--- _-= Per source details. Do not edit below this line.=-_

Source: kam193 (9f8b8630f88afc0b4a1aedeefb4e20adbf3fb9dea06f64747fb0bdf65c0a7bc1) 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

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 1 · created ·

    Published from osv record MAL-2026-18432

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: mal-2026-18432

Advisory: Malicious code in pystr-codec (PyPI)
IDs: mal-2026-18432
Record: https://patchnext.com/advisories/mal-2026-18432 (revision 1, source checked 1 Nov 2026, 06:10 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Unrated
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor response not established. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI pystr-codec: affected >= 0.1.0, <= 0.1.0; >= 0.1.1, <= 0.1.1; >= 0.1.2, <= 0.1.2

## Suggested inspection (read-only)
- `python -m pip show pystr-codec`: prints the installed version. Run with the environment that serves production active.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on pystr-codec.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/MAL-2026-18432 (OSV record MAL-2026-18432 lists affected ranges: PyPI pystr-codec >=0.1.0 =0.1.1 =0.1.2 <=0.1.2)

Commands are suggestions: review each one before running it.

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