CVE-2026-42085 is a medium-severity (CVSS 4.3) CWE-23 vulnerability in openc3. A fix is available for openc3 — see the affected versions and patch details below.
OpenC3 COSMOS: Arbitrary write to plugins directory via path-traversed config filenames
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-42085.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
openc3💎openc3Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.
Description
Summary
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.
Details
In function save_tool_config() (local_mode.rb) responsible for saving user-supplied tool configuration, the desired saving directory is not sufficiently enforced, instead allowing writes inside entire OPENC3_LOCAL_MODE_PATH.
PoC
- Navigate to any tool that enables “Save Configuration” option in left-hand drop-down menu (here Limits Monitor as an example)
- Save a new config with path traversal name using “../” sequences to escape desired directory (up to 3 levels high)
- Observe new files created in /plugins directory by inspecting docker container directly (
openc3-COSMOS-cmd-tlm-api) or using Bucket Explorer (plugin_default)
Impact
Modifying the data of other plugins
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | openc3 | all versions | 6.10.5bundle update openc3 --conservative |
| 💎RubyGems | openc3 | ≥ 7.0.0.pre.rc1&&< 7.0.0-rc3 | 7.0.0-rc3bundle update openc3 --conservative |
Affected Products
cosmosopenc3Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for openc3, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update openc3 to 6.10.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-42085 is resolved across your whole dependency graph.
Workarounds
Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.
Frequently Asked Questions
Is CVE-2026-42085 in your dependencies?
Find it across RubyGems, including transitive dependencies.