CVE-2026-42086

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.

Details

The unsafe eval() usage on user-supplied ARRAY parameters happens in convertToValue method in CommandSender.vue

PoC

1. Using a drop-down form, choose any command that supports ARRAY parameters,
2. Inside square brackets “[…]” place a JavaScript code to be executed
3. Send command to CmdTlmServer using dedicated “Send” button
4. Observe JavaScript code being executed in the current browser session context

Below example uses INST ARYCMD to execute simple JavaScript code snippet alert(“XSS”).

Local JavaScript execution in the user's browser

Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.

CVE-2026-42086 has a CVSS score of 4.6 (Medium). The vector is network-reachable, low privileges required, and user interaction required. 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 (7.0.0); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-42086? CVE-2026-42086 is a medium-severity cross-site scripting (XSS) vulnerability in openc3 (rubygems), affecting versions < 7.0.0. It is fixed in 7.0.0. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
2. How severe is CVE-2026-42086? CVE-2026-42086 has a CVSS score of 4.6 (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-2026-42086? openc3 (rubygems) versions < 7.0.0 is affected.
4. Is there a fix for CVE-2026-42086? Yes. CVE-2026-42086 is fixed in 7.0.0. Upgrade to this version or later.
5. Is CVE-2026-42086 exploitable, and should I be worried? Whether CVE-2026-42086 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-2026-42086 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-2026-42086?
   • Upgrade openc3 to 7.0.0 or later
   • Upgrade openc3 to 7.0.0 or later