CVE-2026-42085

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

1. Navigate to any tool that enables “Save Configuration” option in left-hand drop-down menu (here Limits Monitor as an example)
2. Save a new config with path traversal name using “../” sequences to escape desired directory (up to 3 levels high)
3. Observe new files created in /plugins directory by inspecting docker container directly (openc3-COSMOS-cmd-tlm-api) or using Bucket Explorer (plugin_default)

Modifying the data of other plugins

CVE-2026-42085 has a CVSS score of 4.3 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (6.10.5, 7.0.0-rc3); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-42085? CVE-2026-42085 is a medium-severity security vulnerability in openc3 (rubygems), affecting versions < 6.10.5. It is fixed in 6.10.5, 7.0.0-rc3.
2. How severe is CVE-2026-42085? CVE-2026-42085 has a CVSS score of 4.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of openc3 are affected by CVE-2026-42085? openc3 (rubygems) versions < 6.10.5 is affected.
4. Is there a fix for CVE-2026-42085? Yes. CVE-2026-42085 is fixed in 6.10.5, 7.0.0-rc3. Upgrade to this version or later.
5. Is CVE-2026-42085 exploitable, and should I be worried? Whether CVE-2026-42085 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-42085 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-42085?
   • Upgrade openc3 to 6.10.5 or later
   • Upgrade openc3 to 7.0.0-rc3 or later