CVE-2026-42086: OpenC3 COSMOS: Self-XSS in the Command Sender

Severity: medium (CVSS 4.6 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-05-04 · updated 2026-10-26
Weakness: CWE-79

Description

OpenC3 COSMOS provides the functionality needed to send commands to and receive data from one or more embedded systems. Prior to version 7.0.0, the Command Sender UI uses an unsafe eval() function on array-like command parameters, which allows a user-supplied payload to execute in the browser when sending a command. This creates a self-XSS risk because an attacker can trigger their own script execution in the victim’s session, if allowed to influence the array parameter input, for example via phishing. If successful, an attacker may read or modify data in the authenticated browser context, including session tokens in local storage. This issue has been patched in version 7.0.0.

Affected products

OpenC3 cosmos: before 7.0.0; 7.0.0-rc1, 7.0.0-rc2, 7.0.0-rc3 — fixed in 7.0.0

How to fix

Upgrade to a fixed version: OpenC3 cosmos 7.0.0. Check the vendor advisory for mitigations.

References

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